Re: PCM not letting heat/AC blower blow?
 

This looks like a subset of what I have been working from

"The blower motor relay is installed in a wire har-
ness connector that is secured to the passenger side
outboard end of the HVAC housing in the passenger
compartment, next to the HVAC wire harness con-
nector."

No, it isn't. I even pulled the glove box apart just to be sure.

But thanks anyway.

Carl K


L.W.(Bill) ------ III wrote:
> http://www.----------.com/blower.pdf
> God Bless America, Bill O|||||||O
> mailto:--------------------
>
> Carl K wrote:
>> Whoops.
>> Good Q - how did that happen?
>>
>> Bat+ -- 40A fuse -- blower motor -- resistor pack == switch --x- relay switch
>> -y-- PCM? -- Ground.
>>
>> The relay coil side is driven by the ignition switch and the air flow control
>> switch (off and 7 on's: max, norm, bi, vent, heat, heat/def, def)
>>
>> If I ground X, the blower blows and I can adjust the speed with the speed
>> switch: low to high (no off).
>>
>> If I ground Y, the blower only blows when the relay is engaged: ignition and air
>> flow control switch on.
>>
>> If the far side of the relay was just going to ground, where would the wire
>> terminate?
>>
>> The relay is mounted inside the box that the 3 controls are in: fan speed, air
>> flow and hot/cold. if you look at the back of the box, you can see the 4
>> connectors, you have to disassemble the box to pull the relay out.
>>
>> I am hung up on it going to the PCM just because of the XJ wiring diagram I
>> have. but it is significantly different (like the relay is between the 40A
>> fuse and the motor) , so it won't surprise me if it just goes to ground.
>>
>> Carl K

Re: PCM not letting heat/AC blower blow?
 

The ZJ's automatic temp control system has it's own microprocessor as
part of the control head assembly. The blower speeds are variable and
controlled by this processor. A relay is used for high speed operation
only.

In the manual system, the blower is connected to fuse 7(40A) in the
power distribution center. The resistor pack comes after and is wired
through the fan speed switch which provides the ground path in series
with mode knob. The resistor pack is bypassed at the speed switch for
high speed operation. A relay which is part of the control head assembly
completes the ground connection between the speed switch and the mode
knob when the ignition is on. The relay gets power from fuse 12(10A) in
the junction block which also powers the blend door and panel
illumination. There are 2 ground wires coming off the control assembly,
a VT/WT for the fuse 12 circuit and a DG for the blower switch circuit.

Fuses 18 and 21 in the PDC are also used for AC operation. The
connection to the PCM is an input to the PCM that tells it the AC is on
and has nothing to do with blower speed. I believe the PCM raises the
idle speed slightly in response.

In article <LqWdne-5K4JAdiPZnZ2dnUVZ_qmdnZ2d@comcast.com>,
carl@personnelware.com says...
> Mike wrote:
> > "Carl K" <carl@personnelware.com> wrote in message
> > news:Ad-dnScCL541OCPZnZ2dnUVZ_qWdnZ2d@comcast.com...
> >> Mike wrote:
> >>> "Carl K" <carl@personnelware.com> wrote in message
> >>> news:pOydnfaDzraa6iPZnZ2dnUVZ_radnZ2d@comcast.com. ..
> >>>> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >>>> the == is 4 wires, 1 for each speed
> >>>>
> >>>> If I hook the far side of the relay to ground, the blower blows. The
> >>>> relay is controlled by both ignition and vent selector, so just making a
> >>>> permanent connection to ground would leave me with a fully functional
> >>>> system.
> >>>>
> >>>> But before I go with that hack, wondering if I am missing something?
> >>>>
> >>>> The PCM is $480+installation required to program it.
> >>>>
> >>>> Will a "diagnostic code reader" ($99 from local auto store) tell me if
> >>>> the PCM is not letting the blower blow?
> >>>>
> >>>> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a
> >>>> 'delux' that works on "all cars" and gives descriptions. the 97 is the
> >>>> only car I have that has any sort of diag system (like it will do my 68
> >>>> pickup any good) - and I somehow doubt the delux will really tell me
> >>>> everything I need to know anyway. any comments?
> >>>>
> >>>>
> >>>> Carl K
> >>> The PCM has nothing to do with your blower motor. What type of heat/
> >>> A/C controls do you have ? There are two choices, ATM ( Automatic temp
> >>> control ) or manual control. The wiring is totally different depending on
> >>> which one you have.
> >> Manual switches.
> >>
> >> I have a 97, this is for a 98:
> >>
> >> "The PCM manages air-conditioning compressor and coolant-fan operation,
> >> but it has to see the correct incoming signals before sending outgoing
> >> commands. When the climate-control head is switched to A/C-on mode, a
> >> signal is sent to the PCM. The PCM must also receive a signal from the A/C
> >> low- and high-prcoolant-fan operationessure switches before it turns on
> >> the compressor and/or coolant fan. These switches prevent damage to the
> >> system. I'm not sure what method you used to check for a sufficient charge
> >> of R-134a refrigerant, but a low charge will kill the signal from the
> >> low-pressure switch and therefore prevent the system from working. It
> >> could be a low refrigerant charge, defective PCM, faulty climate-control
> >> head, one of the pressure switches on the blink, a break in related power,
> >> or an issue with the ground circuit wiring."
> >
> >
> > The above info is in reference to an ATC system not a manual system. The
> > wiring is completely different from one to the other. Also, it talks about
> > the PCM controlling the A/C compressor and the coolant fan. That is all the
> > PCM controls and it is the same with either system.
> >
> >
> >> http://trucktrend.com/features/advic...rd_ranger.html
> >>
> >> Isn't the "coolant-fan operation" the "blower motor" ?
> >
> >
> > No. The coolant fan motor is the radiator fan.
>
> ah - I was wondering why it was called something other than "blower motor."
>
> >
> >> I am hoping for something else besides the PCM between the relay and the
> >> Battery(-), like an relay or some other $20 part.
> >> C
> >
> > The PCM does not have anything to do with the blower motor.
> >
> > From what you stated above:
> >
> > "Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >
> > That's fairly close. It is actually alot simpler. Bat + -- 40A fuse --
> > blower motor -- resistor pack -- switch -- Ground.
> >
> > The blower motor switch uses the resistor pack to vary the resistance on
> > the ground side of the blower motor to change speeds. For high speed the
> > resistor is bypassed comepletely.
> >
> >
> > From your other post, so this is easier to follow. You stated :
> >
> >>> If I hook the far side of the relay to ground, the blower blows.
> >
> > and I can control the speed with the switch.
> >
> > Good Q - how did that happen?
>
> > The wiring diagram shows no relay in the circuit at all. Are you shure
> > that you have a relay ? Were is this relay located ?
> >
> >
>
> Whoops.
> Good Q - how did that happen?
>
>
> Bat+ -- 40A fuse -- blower motor -- resistor pack == switch --x- relay switch
> -y-- PCM? -- Ground.
>
> The relay coil side is driven by the ignition switch and the air flow control
> switch (off and 7 on's: max, norm, bi, vent, heat, heat/def, def)
>
> If I ground X, the blower blows and I can adjust the speed with the speed
> switch: low to high (no off).
>
> If I ground Y, the blower only blows when the relay is engaged: ignition and air
> flow control switch on.
>
> If the far side of the relay was just going to ground, where would the wire
> terminate?
>
> The relay is mounted inside the box that the 3 controls are in: fan speed, air
> flow and hot/cold. if you look at the back of the box, you can see the 4
> connectors, you have to disassemble the box to pull the relay out.
>
> I am hung up on it going to the PCM just because of the XJ wiring diagram I
> have. but it is significantly different (like the relay is between the 40A
> fuse and the motor) , so it won't surprise me if it just goes to ground.
>
> Carl K
>

Re: PCM not letting heat/AC blower blow?
 

The ZJ's automatic temp control system has it's own microprocessor as
part of the control head assembly. The blower speeds are variable and
controlled by this processor. A relay is used for high speed operation
only.

In the manual system, the blower is connected to fuse 7(40A) in the
power distribution center. The resistor pack comes after and is wired
through the fan speed switch which provides the ground path in series
with mode knob. The resistor pack is bypassed at the speed switch for
high speed operation. A relay which is part of the control head assembly
completes the ground connection between the speed switch and the mode
knob when the ignition is on. The relay gets power from fuse 12(10A) in
the junction block which also powers the blend door and panel
illumination. There are 2 ground wires coming off the control assembly,
a VT/WT for the fuse 12 circuit and a DG for the blower switch circuit.

Fuses 18 and 21 in the PDC are also used for AC operation. The
connection to the PCM is an input to the PCM that tells it the AC is on
and has nothing to do with blower speed. I believe the PCM raises the
idle speed slightly in response.

In article <LqWdne-5K4JAdiPZnZ2dnUVZ_qmdnZ2d@comcast.com>,
carl@personnelware.com says...
> Mike wrote:
> > "Carl K" <carl@personnelware.com> wrote in message
> > news:Ad-dnScCL541OCPZnZ2dnUVZ_qWdnZ2d@comcast.com...
> >> Mike wrote:
> >>> "Carl K" <carl@personnelware.com> wrote in message
> >>> news:pOydnfaDzraa6iPZnZ2dnUVZ_radnZ2d@comcast.com. ..
> >>>> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >>>> the == is 4 wires, 1 for each speed
> >>>>
> >>>> If I hook the far side of the relay to ground, the blower blows. The
> >>>> relay is controlled by both ignition and vent selector, so just making a
> >>>> permanent connection to ground would leave me with a fully functional
> >>>> system.
> >>>>
> >>>> But before I go with that hack, wondering if I am missing something?
> >>>>
> >>>> The PCM is $480+installation required to program it.
> >>>>
> >>>> Will a "diagnostic code reader" ($99 from local auto store) tell me if
> >>>> the PCM is not letting the blower blow?
> >>>>
> >>>> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a
> >>>> 'delux' that works on "all cars" and gives descriptions. the 97 is the
> >>>> only car I have that has any sort of diag system (like it will do my 68
> >>>> pickup any good) - and I somehow doubt the delux will really tell me
> >>>> everything I need to know anyway. any comments?
> >>>>
> >>>>
> >>>> Carl K
> >>> The PCM has nothing to do with your blower motor. What type of heat/
> >>> A/C controls do you have ? There are two choices, ATM ( Automatic temp
> >>> control ) or manual control. The wiring is totally different depending on
> >>> which one you have.
> >> Manual switches.
> >>
> >> I have a 97, this is for a 98:
> >>
> >> "The PCM manages air-conditioning compressor and coolant-fan operation,
> >> but it has to see the correct incoming signals before sending outgoing
> >> commands. When the climate-control head is switched to A/C-on mode, a
> >> signal is sent to the PCM. The PCM must also receive a signal from the A/C
> >> low- and high-prcoolant-fan operationessure switches before it turns on
> >> the compressor and/or coolant fan. These switches prevent damage to the
> >> system. I'm not sure what method you used to check for a sufficient charge
> >> of R-134a refrigerant, but a low charge will kill the signal from the
> >> low-pressure switch and therefore prevent the system from working. It
> >> could be a low refrigerant charge, defective PCM, faulty climate-control
> >> head, one of the pressure switches on the blink, a break in related power,
> >> or an issue with the ground circuit wiring."
> >
> >
> > The above info is in reference to an ATC system not a manual system. The
> > wiring is completely different from one to the other. Also, it talks about
> > the PCM controlling the A/C compressor and the coolant fan. That is all the
> > PCM controls and it is the same with either system.
> >
> >
> >> http://trucktrend.com/features/advic...rd_ranger.html
> >>
> >> Isn't the "coolant-fan operation" the "blower motor" ?
> >
> >
> > No. The coolant fan motor is the radiator fan.
>
> ah - I was wondering why it was called something other than "blower motor."
>
> >
> >> I am hoping for something else besides the PCM between the relay and the
> >> Battery(-), like an relay or some other $20 part.
> >> C
> >
> > The PCM does not have anything to do with the blower motor.
> >
> > From what you stated above:
> >
> > "Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >
> > That's fairly close. It is actually alot simpler. Bat + -- 40A fuse --
> > blower motor -- resistor pack -- switch -- Ground.
> >
> > The blower motor switch uses the resistor pack to vary the resistance on
> > the ground side of the blower motor to change speeds. For high speed the
> > resistor is bypassed comepletely.
> >
> >
> > From your other post, so this is easier to follow. You stated :
> >
> >>> If I hook the far side of the relay to ground, the blower blows.
> >
> > and I can control the speed with the switch.
> >
> > Good Q - how did that happen?
>
> > The wiring diagram shows no relay in the circuit at all. Are you shure
> > that you have a relay ? Were is this relay located ?
> >
> >
>
> Whoops.
> Good Q - how did that happen?
>
>
> Bat+ -- 40A fuse -- blower motor -- resistor pack == switch --x- relay switch
> -y-- PCM? -- Ground.
>
> The relay coil side is driven by the ignition switch and the air flow control
> switch (off and 7 on's: max, norm, bi, vent, heat, heat/def, def)
>
> If I ground X, the blower blows and I can adjust the speed with the speed
> switch: low to high (no off).
>
> If I ground Y, the blower only blows when the relay is engaged: ignition and air
> flow control switch on.
>
> If the far side of the relay was just going to ground, where would the wire
> terminate?
>
> The relay is mounted inside the box that the 3 controls are in: fan speed, air
> flow and hot/cold. if you look at the back of the box, you can see the 4
> connectors, you have to disassemble the box to pull the relay out.
>
> I am hung up on it going to the PCM just because of the XJ wiring diagram I
> have. but it is significantly different (like the relay is between the 40A
> fuse and the motor) , so it won't surprise me if it just goes to ground.
>
> Carl K
>

Re: PCM not letting heat/AC blower blow?
 

The ZJ's automatic temp control system has it's own microprocessor as
part of the control head assembly. The blower speeds are variable and
controlled by this processor. A relay is used for high speed operation
only.

In the manual system, the blower is connected to fuse 7(40A) in the
power distribution center. The resistor pack comes after and is wired
through the fan speed switch which provides the ground path in series
with mode knob. The resistor pack is bypassed at the speed switch for
high speed operation. A relay which is part of the control head assembly
completes the ground connection between the speed switch and the mode
knob when the ignition is on. The relay gets power from fuse 12(10A) in
the junction block which also powers the blend door and panel
illumination. There are 2 ground wires coming off the control assembly,
a VT/WT for the fuse 12 circuit and a DG for the blower switch circuit.

Fuses 18 and 21 in the PDC are also used for AC operation. The
connection to the PCM is an input to the PCM that tells it the AC is on
and has nothing to do with blower speed. I believe the PCM raises the
idle speed slightly in response.

In article <LqWdne-5K4JAdiPZnZ2dnUVZ_qmdnZ2d@comcast.com>,
carl@personnelware.com says...
> Mike wrote:
> > "Carl K" <carl@personnelware.com> wrote in message
> > news:Ad-dnScCL541OCPZnZ2dnUVZ_qWdnZ2d@comcast.com...
> >> Mike wrote:
> >>> "Carl K" <carl@personnelware.com> wrote in message
> >>> news:pOydnfaDzraa6iPZnZ2dnUVZ_radnZ2d@comcast.com. ..
> >>>> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >>>> the == is 4 wires, 1 for each speed
> >>>>
> >>>> If I hook the far side of the relay to ground, the blower blows. The
> >>>> relay is controlled by both ignition and vent selector, so just making a
> >>>> permanent connection to ground would leave me with a fully functional
> >>>> system.
> >>>>
> >>>> But before I go with that hack, wondering if I am missing something?
> >>>>
> >>>> The PCM is $480+installation required to program it.
> >>>>
> >>>> Will a "diagnostic code reader" ($99 from local auto store) tell me if
> >>>> the PCM is not letting the blower blow?
> >>>>
> >>>> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a
> >>>> 'delux' that works on "all cars" and gives descriptions. the 97 is the
> >>>> only car I have that has any sort of diag system (like it will do my 68
> >>>> pickup any good) - and I somehow doubt the delux will really tell me
> >>>> everything I need to know anyway. any comments?
> >>>>
> >>>>
> >>>> Carl K
> >>> The PCM has nothing to do with your blower motor. What type of heat/
> >>> A/C controls do you have ? There are two choices, ATM ( Automatic temp
> >>> control ) or manual control. The wiring is totally different depending on
> >>> which one you have.
> >> Manual switches.
> >>
> >> I have a 97, this is for a 98:
> >>
> >> "The PCM manages air-conditioning compressor and coolant-fan operation,
> >> but it has to see the correct incoming signals before sending outgoing
> >> commands. When the climate-control head is switched to A/C-on mode, a
> >> signal is sent to the PCM. The PCM must also receive a signal from the A/C
> >> low- and high-prcoolant-fan operationessure switches before it turns on
> >> the compressor and/or coolant fan. These switches prevent damage to the
> >> system. I'm not sure what method you used to check for a sufficient charge
> >> of R-134a refrigerant, but a low charge will kill the signal from the
> >> low-pressure switch and therefore prevent the system from working. It
> >> could be a low refrigerant charge, defective PCM, faulty climate-control
> >> head, one of the pressure switches on the blink, a break in related power,
> >> or an issue with the ground circuit wiring."
> >
> >
> > The above info is in reference to an ATC system not a manual system. The
> > wiring is completely different from one to the other. Also, it talks about
> > the PCM controlling the A/C compressor and the coolant fan. That is all the
> > PCM controls and it is the same with either system.
> >
> >
> >> http://trucktrend.com/features/advic...rd_ranger.html
> >>
> >> Isn't the "coolant-fan operation" the "blower motor" ?
> >
> >
> > No. The coolant fan motor is the radiator fan.
>
> ah - I was wondering why it was called something other than "blower motor."
>
> >
> >> I am hoping for something else besides the PCM between the relay and the
> >> Battery(-), like an relay or some other $20 part.
> >> C
> >
> > The PCM does not have anything to do with the blower motor.
> >
> > From what you stated above:
> >
> > "Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >
> > That's fairly close. It is actually alot simpler. Bat + -- 40A fuse --
> > blower motor -- resistor pack -- switch -- Ground.
> >
> > The blower motor switch uses the resistor pack to vary the resistance on
> > the ground side of the blower motor to change speeds. For high speed the
> > resistor is bypassed comepletely.
> >
> >
> > From your other post, so this is easier to follow. You stated :
> >
> >>> If I hook the far side of the relay to ground, the blower blows.
> >
> > and I can control the speed with the switch.
> >
> > Good Q - how did that happen?
>
> > The wiring diagram shows no relay in the circuit at all. Are you shure
> > that you have a relay ? Were is this relay located ?
> >
> >
>
> Whoops.
> Good Q - how did that happen?
>
>
> Bat+ -- 40A fuse -- blower motor -- resistor pack == switch --x- relay switch
> -y-- PCM? -- Ground.
>
> The relay coil side is driven by the ignition switch and the air flow control
> switch (off and 7 on's: max, norm, bi, vent, heat, heat/def, def)
>
> If I ground X, the blower blows and I can adjust the speed with the speed
> switch: low to high (no off).
>
> If I ground Y, the blower only blows when the relay is engaged: ignition and air
> flow control switch on.
>
> If the far side of the relay was just going to ground, where would the wire
> terminate?
>
> The relay is mounted inside the box that the 3 controls are in: fan speed, air
> flow and hot/cold. if you look at the back of the box, you can see the 4
> connectors, you have to disassemble the box to pull the relay out.
>
> I am hung up on it going to the PCM just because of the XJ wiring diagram I
> have. but it is significantly different (like the relay is between the 40A
> fuse and the motor) , so it won't surprise me if it just goes to ground.
>
> Carl K
>

Re: PCM not letting heat/AC blower blow?
 

The ZJ's automatic temp control system has it's own microprocessor as
part of the control head assembly. The blower speeds are variable and
controlled by this processor. A relay is used for high speed operation
only.

In the manual system, the blower is connected to fuse 7(40A) in the
power distribution center. The resistor pack comes after and is wired
through the fan speed switch which provides the ground path in series
with mode knob. The resistor pack is bypassed at the speed switch for
high speed operation. A relay which is part of the control head assembly
completes the ground connection between the speed switch and the mode
knob when the ignition is on. The relay gets power from fuse 12(10A) in
the junction block which also powers the blend door and panel
illumination. There are 2 ground wires coming off the control assembly,
a VT/WT for the fuse 12 circuit and a DG for the blower switch circuit.

Fuses 18 and 21 in the PDC are also used for AC operation. The
connection to the PCM is an input to the PCM that tells it the AC is on
and has nothing to do with blower speed. I believe the PCM raises the
idle speed slightly in response.

In article <LqWdne-5K4JAdiPZnZ2dnUVZ_qmdnZ2d@comcast.com>,
carl@personnelware.com says...
> Mike wrote:
> > "Carl K" <carl@personnelware.com> wrote in message
> > news:Ad-dnScCL541OCPZnZ2dnUVZ_qWdnZ2d@comcast.com...
> >> Mike wrote:
> >>> "Carl K" <carl@personnelware.com> wrote in message
> >>> news:pOydnfaDzraa6iPZnZ2dnUVZ_radnZ2d@comcast.com. ..
> >>>> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >>>> the == is 4 wires, 1 for each speed
> >>>>
> >>>> If I hook the far side of the relay to ground, the blower blows. The
> >>>> relay is controlled by both ignition and vent selector, so just making a
> >>>> permanent connection to ground would leave me with a fully functional
> >>>> system.
> >>>>
> >>>> But before I go with that hack, wondering if I am missing something?
> >>>>
> >>>> The PCM is $480+installation required to program it.
> >>>>
> >>>> Will a "diagnostic code reader" ($99 from local auto store) tell me if
> >>>> the PCM is not letting the blower blow?
> >>>>
> >>>> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a
> >>>> 'delux' that works on "all cars" and gives descriptions. the 97 is the
> >>>> only car I have that has any sort of diag system (like it will do my 68
> >>>> pickup any good) - and I somehow doubt the delux will really tell me
> >>>> everything I need to know anyway. any comments?
> >>>>
> >>>>
> >>>> Carl K
> >>> The PCM has nothing to do with your blower motor. What type of heat/
> >>> A/C controls do you have ? There are two choices, ATM ( Automatic temp
> >>> control ) or manual control. The wiring is totally different depending on
> >>> which one you have.
> >> Manual switches.
> >>
> >> I have a 97, this is for a 98:
> >>
> >> "The PCM manages air-conditioning compressor and coolant-fan operation,
> >> but it has to see the correct incoming signals before sending outgoing
> >> commands. When the climate-control head is switched to A/C-on mode, a
> >> signal is sent to the PCM. The PCM must also receive a signal from the A/C
> >> low- and high-prcoolant-fan operationessure switches before it turns on
> >> the compressor and/or coolant fan. These switches prevent damage to the
> >> system. I'm not sure what method you used to check for a sufficient charge
> >> of R-134a refrigerant, but a low charge will kill the signal from the
> >> low-pressure switch and therefore prevent the system from working. It
> >> could be a low refrigerant charge, defective PCM, faulty climate-control
> >> head, one of the pressure switches on the blink, a break in related power,
> >> or an issue with the ground circuit wiring."
> >
> >
> > The above info is in reference to an ATC system not a manual system. The
> > wiring is completely different from one to the other. Also, it talks about
> > the PCM controlling the A/C compressor and the coolant fan. That is all the
> > PCM controls and it is the same with either system.
> >
> >
> >> http://trucktrend.com/features/advic...rd_ranger.html
> >>
> >> Isn't the "coolant-fan operation" the "blower motor" ?
> >
> >
> > No. The coolant fan motor is the radiator fan.
>
> ah - I was wondering why it was called something other than "blower motor."
>
> >
> >> I am hoping for something else besides the PCM between the relay and the
> >> Battery(-), like an relay or some other $20 part.
> >> C
> >
> > The PCM does not have anything to do with the blower motor.
> >
> > From what you stated above:
> >
> > "Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to
> >>>> the library to confirm - Haynes wiring didn't have it.)
> >>>>
> >>>> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> >>>> Powertrain Control Module -- Battery(-)
> >>>>
> >
> > That's fairly close. It is actually alot simpler. Bat + -- 40A fuse --
> > blower motor -- resistor pack -- switch -- Ground.
> >
> > The blower motor switch uses the resistor pack to vary the resistance on
> > the ground side of the blower motor to change speeds. For high speed the
> > resistor is bypassed comepletely.
> >
> >
> > From your other post, so this is easier to follow. You stated :
> >
> >>> If I hook the far side of the relay to ground, the blower blows.
> >
> > and I can control the speed with the switch.
> >
> > Good Q - how did that happen?
>
> > The wiring diagram shows no relay in the circuit at all. Are you shure
> > that you have a relay ? Were is this relay located ?
> >
> >
>
> Whoops.
> Good Q - how did that happen?
>
>
> Bat+ -- 40A fuse -- blower motor -- resistor pack == switch --x- relay switch
> -y-- PCM? -- Ground.
>
> The relay coil side is driven by the ignition switch and the air flow control
> switch (off and 7 on's: max, norm, bi, vent, heat, heat/def, def)
>
> If I ground X, the blower blows and I can adjust the speed with the speed
> switch: low to high (no off).
>
> If I ground Y, the blower only blows when the relay is engaged: ignition and air
> flow control switch on.
>
> If the far side of the relay was just going to ground, where would the wire
> terminate?
>
> The relay is mounted inside the box that the 3 controls are in: fan speed, air
> flow and hot/cold. if you look at the back of the box, you can see the 4
> connectors, you have to disassemble the box to pull the relay out.
>
> I am hung up on it going to the PCM just because of the XJ wiring diagram I
> have. but it is significantly different (like the relay is between the 40A
> fuse and the motor) , so it won't surprise me if it just goes to ground.
>
> Carl K
>

Re: PCM not letting heat/AC blower blow?
 

the pcm comes progamed new from dc if you get it from them and carquest sells them
too
more than likely the blower not working is the resistor since u can make the blower
work do u have atc if u do it can store codes thet can be pulled from the dash thru
it but u need factory book to do so and thats were i would start

Carl K wrote:

> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to the
> library to confirm - Haynes wiring didn't have it.)
>
> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> Powertrain Control Module -- Battery(-)
>
> the == is 4 wires, 1 for each speed
>
> If I hook the far side of the relay to ground, the blower blows. The relay is
> controlled by both ignition and vent selector, so just making a permanent
> connection to ground would leave me with a fully functional system.
>
> But before I go with that hack, wondering if I am missing something?
>
> The PCM is $480+installation required to program it.
>
> Will a "diagnostic code reader" ($99 from local auto store) tell me if the PCM
> is not letting the blower blow?
>
> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a 'delux'
> that works on "all cars" and gives descriptions. the 97 is the only car I have
> that has any sort of diag system (like it will do my 68 pickup any good) - and I
> somehow doubt the delux will really tell me everything I need to know anyway.
> any comments?
>
> Carl K

Re: PCM not letting heat/AC blower blow?
 

the pcm comes progamed new from dc if you get it from them and carquest sells them
too
more than likely the blower not working is the resistor since u can make the blower
work do u have atc if u do it can store codes thet can be pulled from the dash thru
it but u need factory book to do so and thats were i would start

Carl K wrote:

> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to the
> library to confirm - Haynes wiring didn't have it.)
>
> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> Powertrain Control Module -- Battery(-)
>
> the == is 4 wires, 1 for each speed
>
> If I hook the far side of the relay to ground, the blower blows. The relay is
> controlled by both ignition and vent selector, so just making a permanent
> connection to ground would leave me with a fully functional system.
>
> But before I go with that hack, wondering if I am missing something?
>
> The PCM is $480+installation required to program it.
>
> Will a "diagnostic code reader" ($99 from local auto store) tell me if the PCM
> is not letting the blower blow?
>
> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a 'delux'
> that works on "all cars" and gives descriptions. the 97 is the only car I have
> that has any sort of diag system (like it will do my 68 pickup any good) - and I
> somehow doubt the delux will really tell me everything I need to know anyway.
> any comments?
>
> Carl K

Re: PCM not letting heat/AC blower blow?
 

the pcm comes progamed new from dc if you get it from them and carquest sells them
too
more than likely the blower not working is the resistor since u can make the blower
work do u have atc if u do it can store codes thet can be pulled from the dash thru
it but u need factory book to do so and thats were i would start

Carl K wrote:

> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to the
> library to confirm - Haynes wiring didn't have it.)
>
> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> Powertrain Control Module -- Battery(-)
>
> the == is 4 wires, 1 for each speed
>
> If I hook the far side of the relay to ground, the blower blows. The relay is
> controlled by both ignition and vent selector, so just making a permanent
> connection to ground would leave me with a fully functional system.
>
> But before I go with that hack, wondering if I am missing something?
>
> The PCM is $480+installation required to program it.
>
> Will a "diagnostic code reader" ($99 from local auto store) tell me if the PCM
> is not letting the blower blow?
>
> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a 'delux'
> that works on "all cars" and gives descriptions. the 97 is the only car I have
> that has any sort of diag system (like it will do my 68 pickup any good) - and I
> somehow doubt the delux will really tell me everything I need to know anyway.
> any comments?
>
> Carl K

Re: PCM not letting heat/AC blower blow?
 

the pcm comes progamed new from dc if you get it from them and carquest sells them
too
more than likely the blower not working is the resistor since u can make the blower
work do u have atc if u do it can store codes thet can be pulled from the dash thru
it but u need factory book to do so and thats were i would start

Carl K wrote:

> Pretty sure this is how my 97 Grand Cherokee is wired: (I may make it to the
> library to confirm - Haynes wiring didn't have it.)
>
> Battery(+) -- 40A fuse -- motor -- resistor pack == switch -- relay --
> Powertrain Control Module -- Battery(-)
>
> the == is 4 wires, 1 for each speed
>
> If I hook the far side of the relay to ground, the blower blows. The relay is
> controlled by both ignition and vent selector, so just making a permanent
> connection to ground would leave me with a fully functional system.
>
> But before I go with that hack, wondering if I am missing something?
>
> The PCM is $480+installation required to program it.
>
> Will a "diagnostic code reader" ($99 from local auto store) tell me if the PCM
> is not letting the blower blow?
>
> Also, $99 gets me "just numeric codes for '96 and up" but $250 get a 'delux'
> that works on "all cars" and gives descriptions. the 97 is the only car I have
> that has any sort of diag system (like it will do my 68 pickup any good) - and I
> somehow doubt the delux will really tell me everything I need to know anyway.
> any comments?
>
> Carl K