A/C clutch relay does not close
08-04-2006, 10:34 PM
#21
Guest
Posts: n/a
Re: A/C clutch relay does not close
you may have the famous leaking evap.coil and there is not a sufficient
charge to operate the system
"L.W.(Bill) ------ III" wrote:
> May have a bad low pressure switch:
> http://members.***.net/wilsond/Fixes...s.html#sensors
> God Bless America, Bill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> carybriel@hotmail.com wrote:
> >
> > I have a 99 jeep cherokee classic. I have a problem where the A/C
> > clutch does not engage at all. I can manually engage it by manually
> > engaging the A/C clutch relay in the relay box under the hood. When
> > the clutch is manually engaged by manually closing the A/C clutch
> > relay, the A/C blows cold air. I checked the 20A fuse for the A/C
> > clutch, also located in the relay box, and it is OK. I checked the
> > relay itself to insure that applying 12V to it would cause it to close,
> > and it appears to be OK (it does not appear that the relay itself is
> > bad). I looked at the control unit in the interior (containing the
> > ***** to control heating and A/C), and it appears that vacuum is used
> > to control heat and A/C function when the **** is rotated to that A/C
> > position, but I can't determine yet how the vacuum system ultimately
> > manages to close the A/C clutch relay. It seems that 12V is not being
> > applied to the A/C clutch relay for some reason, and I have read that
> > there is a pressure switch on the system somewhere. Could it be that
> > the refrigerant is low, even though the system blows cold air when I
> > manually engage the relay? Also, is there a vacuum switch somewhere
> > (under the dash, etc) that is actuated by vacuum when the control ****
> > is rotated into the A/C position, that should be ultimately actuating
> > the A/C clutch relay? Any help would be appreciated. Help! Thanks.
charge to operate the system
"L.W.(Bill) ------ III" wrote:
> May have a bad low pressure switch:
> http://members.***.net/wilsond/Fixes...s.html#sensors
> God Bless America, Bill O|||||||O
> mailto:-------------------- http://www.----------.com/
>
> carybriel@hotmail.com wrote:
> >
> > I have a 99 jeep cherokee classic. I have a problem where the A/C
> > clutch does not engage at all. I can manually engage it by manually
> > engaging the A/C clutch relay in the relay box under the hood. When
> > the clutch is manually engaged by manually closing the A/C clutch
> > relay, the A/C blows cold air. I checked the 20A fuse for the A/C
> > clutch, also located in the relay box, and it is OK. I checked the
> > relay itself to insure that applying 12V to it would cause it to close,
> > and it appears to be OK (it does not appear that the relay itself is
> > bad). I looked at the control unit in the interior (containing the
> > ***** to control heating and A/C), and it appears that vacuum is used
> > to control heat and A/C function when the **** is rotated to that A/C
> > position, but I can't determine yet how the vacuum system ultimately
> > manages to close the A/C clutch relay. It seems that 12V is not being
> > applied to the A/C clutch relay for some reason, and I have read that
> > there is a pressure switch on the system somewhere. Could it be that
> > the refrigerant is low, even though the system blows cold air when I
> > manually engage the relay? Also, is there a vacuum switch somewhere
> > (under the dash, etc) that is actuated by vacuum when the control ****
> > is rotated into the A/C position, that should be ultimately actuating
> > the A/C clutch relay? Any help would be appreciated. Help! Thanks.
08-05-2006, 09:24 PM
#22
Guest
Posts: n/a
Re: A/C clutch relay does not close
Yes, the A/C switch is vacuum/electric.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
08-05-2006, 09:24 PM
#23
Guest
Posts: n/a
Re: A/C clutch relay does not close
Yes, the A/C switch is vacuum/electric.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
08-05-2006, 09:24 PM
#24
Guest
Posts: n/a
Re: A/C clutch relay does not close
Yes, the A/C switch is vacuum/electric.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
08-05-2006, 09:24 PM
#25
Guest
Posts: n/a
Re: A/C clutch relay does not close
Yes, the A/C switch is vacuum/electric.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
The PCM controls the A/C clutch relay.
On 3 Aug 2006 19:35:09 -0700, carybriel@hotmail.com wrote:
>I think I understand your reply, and will check the low pressure switch
>as you suggest. There is one thing that I don't understand though.
>You mention that on the relay side, a switch is involved inside. The
>only **** inside the cab that activates the AC is a rotating **** that
>allows selection of AC functions, as well as selection of heat related
>functions (floor, defrost, etc). Does this rotating **** have an
>integrated electrical switch as well as a vacuum switch? I do not
>believe that this internal switch is bad, but I'm just wondering what
>electically actuates the relay from the inside of the cab. Also, how
>does the powertrain control module figure into the logic of the relay
>side circuit?
>Thanks for the help! I'll check the low pressure switch and let you
>know what I find.
>Cary Briel
>
>
>DougW wrote:
>> L.W.(Bill) ------ III wrote:
>> > May have a bad low pressure switch:
>> > http://members.***.net/wilsond/Fixes...s.html#sensors
>>
>> Yep. You can safely jumper that switch for testing (and for
>> filling) but it's not a fix. The purpose of the low limit is
>> to prevent the AC compressor from burning out due to lack of oil.
>> The low limit switch can kick in when the AC is still capable
>> of delivering cool air.
>>
>> The vac has nothing to do with the clutch or relay, it's
>> purely for moving the doors that direct airflow.
>>
>> The clutch circuit is
>>
>> battery >-->fuse>-->lowlimit>-->highlimit>-->AC relay-->clutch solinoid-->ground
>>
>> On the relay side it's a bit more complex and involves the switch inside
>> and the powertrain control module (to control engine RPM).
>>
>> The switch should be <1 ohms (actually 0) unless the system pressure is too low.
>> Thing is system pressure changes based on ambient temperature. That's why
>> filling is best done by volume and not pressure.
>>
>> I would hazzard a guess your less than half a can down. But don't just
>> go throwing more in there, get a pressure gauge kit (not the cheap onthecan one)
>> but at least a good on on the fill hose. or better yet a high/low side set.
>> (all depends on how many times you plan on using it)
>>
>> Most good AC shops will do a refill (and system leak check) for less than 100$
>> It's been a while since I checked prices.
>>
>> > carybriel@hotmail.com wrote:
>> >>
>> >> I have a 99 jeep cherokee classic. I have a problem where the A/C
>> >> clutch does not engage at all. I can manually engage it by manually
>> >> engaging the A/C clutch relay in the relay box under the hood. When
>> >> the clutch is manually engaged by manually closing the A/C clutch
>> >> relay, the A/C blows cold air. I checked the 20A fuse for the A/C
>> >> clutch, also located in the relay box, and it is OK. I checked the
>> >> relay itself to insure that applying 12V to it would cause it to
>> >> close, and it appears to be OK (it does not appear that the relay
>> >> itself is bad). I looked at the control unit in the interior
>> >> (containing the ***** to control heating and A/C), and it appears
>> >> that vacuum is used to control heat and A/C function when the ****
>> >> is rotated to that A/C position, but I can't determine yet how the
>> >> vacuum system ultimately manages to close the A/C clutch relay. It
>> >> seems that 12V is not being applied to the A/C clutch relay for some
>> >> reason, and I have read that there is a pressure switch on the
>> >> system somewhere. Could it be that the refrigerant is low, even
>> >> though the system blows cold air when I manually engage the relay?
>> >> Also, is there a vacuum switch somewhere (under the dash, etc) that
>> >> is actuated by vacuum when the control **** is rotated into the A/C
>> >> position, that should be ultimately actuating the A/C clutch relay?
>> >> Any help would be appreciated. Help! Thanks.
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Rico de Lara
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