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.

 

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.

 

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.

 

carybriel 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.

In Defrost modes the AC is on. In all other modes it's on if the
AC button is illuminated. The **** that controls position from
ducts to bi to defrost has a switch that works in tandam with the
AC button. (manual climate control)
In defrost or any combination of defrost, the AC will run.
Otherwise the AC only runs if the AC button is pressed in.
The light doesn't illuminate in any of the defost settings
even if the compressor is running.

If the light is lit in regular (center/center+floor) mode
then the relay should have power.

--
DougW

 

carybriel 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.

In Defrost modes the AC is on. In all other modes it's on if the
AC button is illuminated. The **** that controls position from
ducts to bi to defrost has a switch that works in tandam with the
AC button. (manual climate control)
In defrost or any combination of defrost, the AC will run.
Otherwise the AC only runs if the AC button is pressed in.
The light doesn't illuminate in any of the defost settings
even if the compressor is running.

If the light is lit in regular (center/center+floor) mode
then the relay should have power.

--
DougW

 

carybriel 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.

In Defrost modes the AC is on. In all other modes it's on if the
AC button is illuminated. The **** that controls position from
ducts to bi to defrost has a switch that works in tandam with the
AC button. (manual climate control)
In defrost or any combination of defrost, the AC will run.
Otherwise the AC only runs if the AC button is pressed in.
The light doesn't illuminate in any of the defost settings
even if the compressor is running.

If the light is lit in regular (center/center+floor) mode
then the relay should have power.

--
DougW

 

carybriel 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.

In Defrost modes the AC is on. In all other modes it's on if the
AC button is illuminated. The **** that controls position from
ducts to bi to defrost has a switch that works in tandam with the
AC button. (manual climate control)
In defrost or any combination of defrost, the AC will run.
Otherwise the AC only runs if the AC button is pressed in.
The light doesn't illuminate in any of the defost settings
even if the compressor is running.

If the light is lit in regular (center/center+floor) mode
then the relay should have power.

--
DougW

 

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.

 

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.

 

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.