Need A/C help on 91' with Climate Control System
Thread Starter
Pro
Joined: Mar 2006
Posts: 649
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From: Georgia
Need A/C help on 91' with Climate Control System
I noticed the air was not blowing cold recently when setting the climate control(digital system) to A/C. I had it checked out at an A/C shop and they said it has plenty of freon and that it is an electrical problem.
I have no clue where to start. At $60/hour I thought I would take a look myself before having a shop trace it down. I have no other electrical problems. I will say that because I have a custom made dash I recently pulled the A/C contoller out from the dash because it didn't look like it lined up right in the dash. I am hoping a wire is crimped or something because the A/C head unit is repositioned in the dash, see picture below. The A/C worked fine after I put it back together(about 6 months ago)
Any help is much appreciated. Thanks!
I have no clue where to start. At $60/hour I thought I would take a look myself before having a shop trace it down. I have no other electrical problems. I will say that because I have a custom made dash I recently pulled the A/C contoller out from the dash because it didn't look like it lined up right in the dash. I am hoping a wire is crimped or something because the A/C head unit is repositioned in the dash, see picture below. The A/C worked fine after I put it back together(about 6 months ago)
Any help is much appreciated. Thanks!
Race Director
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Don't know how a shop could tell you it's charged if the compressor doesn't engage (or does it?) - disconnect and reconnect the battery if there are no faults; then if it still doesn't work, recheck and post the data stream.
Thread Starter
Pro
Joined: Mar 2006
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From: Georgia
I clicked the above link and can get into the codes but don't know what it is telling me.
Can a bad ECM cause the compressor to not come on? As I said above the A/C shop checked and the car has freon. They said it is an electrical problem.
Thanks again for the help.
Last edited by VinceAD; Jun 12, 2009 at 09:14 PM.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Post whatever info you get out of the Controls - the numbers can be interpreted.
Did the shop give you operating pressures (required in CA)?
Assuming there's gas - have you tried a new compressor Relay?
Basically, the ECM controls compressor engagement. An ac request flows via a serial data line to the processor (Programmer) which sends it to the ECM. If there's a voltage signal from the Pressure Sensor, the ECM drives (grounds) the compressor relay. In line with that relay is a Low Pressure Switch. The contacts in that Switch will be closed if there's gas in it and the clutch should engage. The ECM then looks for a voltage increase from the Pressure Sensor meaning the compressor is doing it's job. If there isn't one, it removes ground from the compressor relay. Otherwise, if there isn't enough gas or if there isn't enough pressure to keep the Low Pressure Switch contacts closed (usually below 50 degrees), the circuit is broken to the Compressor. And/or if the Low Pressure Switch contacts start to open and close rapidly, the ECM interprets that as a no gas condition and shuts down the clutch driver until it's fixed.
If it's got gas, the Relay is good and there's no trouble codes, the most obvious fault is the Low Pressure Switch. Use a DVM to see if the switch is closed. If not, replace it. If the contacts are closed, jumper the harness with a paperclip. If it runs and blows cold, the connector is bad - wriggle it around - hold it onto the switch and see if that makes it run.
Did the shop give you operating pressures (required in CA)?
Assuming there's gas - have you tried a new compressor Relay?
Basically, the ECM controls compressor engagement. An ac request flows via a serial data line to the processor (Programmer) which sends it to the ECM. If there's a voltage signal from the Pressure Sensor, the ECM drives (grounds) the compressor relay. In line with that relay is a Low Pressure Switch. The contacts in that Switch will be closed if there's gas in it and the clutch should engage. The ECM then looks for a voltage increase from the Pressure Sensor meaning the compressor is doing it's job. If there isn't one, it removes ground from the compressor relay. Otherwise, if there isn't enough gas or if there isn't enough pressure to keep the Low Pressure Switch contacts closed (usually below 50 degrees), the circuit is broken to the Compressor. And/or if the Low Pressure Switch contacts start to open and close rapidly, the ECM interprets that as a no gas condition and shuts down the clutch driver until it's fixed.
If it's got gas, the Relay is good and there's no trouble codes, the most obvious fault is the Low Pressure Switch. Use a DVM to see if the switch is closed. If not, replace it. If the contacts are closed, jumper the harness with a paperclip. If it runs and blows cold, the connector is bad - wriggle it around - hold it onto the switch and see if that makes it run.
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Thread Starter
Pro
Joined: Mar 2006
Posts: 649
Likes: 3
From: Georgia
Post whatever info you get out of the Controls - the numbers can be interpreted.
Did the shop give you operating pressures (required in CA)?
Assuming there's gas - have you tried a new compressor Relay?
Basically, the ECM controls compressor engagement. An ac request flows via a serial data line to the processor (Programmer) which sends it to the ECM. If there's a voltage signal from the Pressure Sensor, the ECM drives (grounds) the compressor relay. In line with that relay is a Low Pressure Switch. The contacts in that Switch will be closed if there's gas in it and the clutch should engage. The ECM then looks for a voltage increase from the Pressure Sensor meaning the compressor is doing it's job. If there isn't one, it removes ground from the compressor relay. Otherwise, if there isn't enough gas or if there isn't enough pressure to keep the Low Pressure Switch contacts closed (usually below 50 degrees), the circuit is broken to the Compressor. And/or if the Low Pressure Switch contacts start to open and close rapidly, the ECM interprets that as a no gas condition and shuts down the clutch driver until it's fixed.
If it's got gas, the Relay is good and there's no trouble codes, the most obvious fault is the Low Pressure Switch. Use a DVM to see if the switch is closed. If not, replace it. If the contacts are closed, jumper the harness with a paperclip. If it runs and blows cold, the connector is bad - wriggle it around - hold it onto the switch and see if that makes it run.
Did the shop give you operating pressures (required in CA)?
Assuming there's gas - have you tried a new compressor Relay?
Basically, the ECM controls compressor engagement. An ac request flows via a serial data line to the processor (Programmer) which sends it to the ECM. If there's a voltage signal from the Pressure Sensor, the ECM drives (grounds) the compressor relay. In line with that relay is a Low Pressure Switch. The contacts in that Switch will be closed if there's gas in it and the clutch should engage. The ECM then looks for a voltage increase from the Pressure Sensor meaning the compressor is doing it's job. If there isn't one, it removes ground from the compressor relay. Otherwise, if there isn't enough gas or if there isn't enough pressure to keep the Low Pressure Switch contacts closed (usually below 50 degrees), the circuit is broken to the Compressor. And/or if the Low Pressure Switch contacts start to open and close rapidly, the ECM interprets that as a no gas condition and shuts down the clutch driver until it's fixed.
If it's got gas, the Relay is good and there's no trouble codes, the most obvious fault is the Low Pressure Switch. Use a DVM to see if the switch is closed. If not, replace it. If the contacts are closed, jumper the harness with a paperclip. If it runs and blows cold, the connector is bad - wriggle it around - hold it onto the switch and see if that makes it run.
-00 > 00
-01 > 64
-02 > 123
-03 > 84
-04 > 198
-05 > 173
-06 > 00
-07 > 00
-09 > 10
-11 > 00
-12 > -155
-16 > 27
-17 > 126
-19 > 100
-20 > 122
-21 > 145
-22 > -133
-23 > 128
-24 > 128
-30 > 38
-31 > 179
-34 > -153
-36 > 00
-37 > 02
I pulled the codes with the ingnition switch on but engine not running (I am assuming this is the correct way to pull the codes) If not I pulled them with the car running and the only differences were in 05(114), 06(34), 09(07), 10(48), 16(45)
Thanks again,
Vince
Thread Starter
Pro
Joined: Mar 2006
Posts: 649
Likes: 3
From: Georgia
Post whatever info you get out of the Controls - the numbers can be interpreted.
Did the shop give you operating pressures (required in CA)?
Assuming there's gas - have you tried a new compressor Relay?
Basically, the ECM controls compressor engagement. An ac request flows via a serial data line to the processor (Programmer) which sends it to the ECM. If there's a voltage signal from the Pressure Sensor, the ECM drives (grounds) the compressor relay. In line with that relay is a Low Pressure Switch. The contacts in that Switch will be closed if there's gas in it and the clutch should engage. The ECM then looks for a voltage increase from the Pressure Sensor meaning the compressor is doing it's job. If there isn't one, it removes ground from the compressor relay. Otherwise, if there isn't enough gas or if there isn't enough pressure to keep the Low Pressure Switch contacts closed (usually below 50 degrees), the circuit is broken to the Compressor. And/or if the Low Pressure Switch contacts start to open and close rapidly, the ECM interprets that as a no gas condition and shuts down the clutch driver until it's fixed.
If it's got gas, the Relay is good and there's no trouble codes, the most obvious fault is the Low Pressure Switch. Use a DVM to see if the switch is closed. If not, replace it. If the contacts are closed, jumper the harness with a paperclip. If it runs and blows cold, the connector is bad - wriggle it around - hold it onto the switch and see if that makes it run.
Did the shop give you operating pressures (required in CA)?
Assuming there's gas - have you tried a new compressor Relay?
Basically, the ECM controls compressor engagement. An ac request flows via a serial data line to the processor (Programmer) which sends it to the ECM. If there's a voltage signal from the Pressure Sensor, the ECM drives (grounds) the compressor relay. In line with that relay is a Low Pressure Switch. The contacts in that Switch will be closed if there's gas in it and the clutch should engage. The ECM then looks for a voltage increase from the Pressure Sensor meaning the compressor is doing it's job. If there isn't one, it removes ground from the compressor relay. Otherwise, if there isn't enough gas or if there isn't enough pressure to keep the Low Pressure Switch contacts closed (usually below 50 degrees), the circuit is broken to the Compressor. And/or if the Low Pressure Switch contacts start to open and close rapidly, the ECM interprets that as a no gas condition and shuts down the clutch driver until it's fixed.
If it's got gas, the Relay is good and there's no trouble codes, the most obvious fault is the Low Pressure Switch. Use a DVM to see if the switch is closed. If not, replace it. If the contacts are closed, jumper the harness with a paperclip. If it runs and blows cold, the connector is bad - wriggle it around - hold it onto the switch and see if that makes it run.
BTW for anyone that reads this thread and wonders where the compressor relay is(on a 91' anyway, which is the last year of the L98 so not sure if it would be in same place with the LT1/LT4 equipped cars)it is under the driver side dash. There are three relays and it is the center one. Just take the cover off from under the dash and it is close to the steering column, you may have to take the metal plate that the cover goes over off to access it.
Thanks,
