A/C not working

[ssbtech]

Before I tear into the service manual and get the multimeter out - the A/C light comes on on the dash but I don't hear the relay or clutch engage, and the second fan doesn't come on.  I've had the A/C relay fail on me before so hopefully a simple fix - but was curious if low refrigerant charge would cause the system to not respond this way. It looks per the wiring diagram that the relay is wired in series with the pressure switch, so it would appear that at least the relay wouldn't engage if the pressure was out of range. 

Tips appreciated!

Thank you :)

[ssbtech]

I'll also add that my exterior ambient temp sensor seems to be giving odd readings, either too warm or too cool.  I have replaced the sensor without resolution.

[Pleides]

Set auto climate control to 65 degrees. Does it come on? A/C does not come on these cars unless using auto climate control and the temperature is 74 or less (given appropriate weather outside) or the manual climate control is set to 65 degrees on both sides of the car with the A/C on. No, it doesn't make sense to me either. I thought my A/C was broken because of this and it turns out that using auto climate control is the best way to get A/C on without having it set to 65.

[ssbtech]

1 hour ago, Pleides said:

Set auto climate control to 65 degrees. Does it come on? A/C does not come on these cars unless using auto climate control and the temperature is 74 or less (given appropriate weather outside) or the manual climate control is set to 65 degrees on both sides of the car with the A/C on. No, it doesn't make sense to me either. I thought my A/C was broken because of this and it turns out that using auto climate control is the best way to get A/C on without having it set to 65.

 

I've not experienced that personally in the 19 years I've had the car.  I'll double-check but I'm pretty sure it's always responded.

[silverton]

quick test is to swap the AC relay with the one right next to it, which iirc is a fan relay, i'd pick the main fan vs sub fan as the sub fan should still engage with the AC button on whether the compressor is running or not. AC defaults to on in either of the windshield defrost modes, and can be turned off on face/feet. the A/C can be turned on and off no matter what temperature is selected when in face/feet mode.

[Pleides]

1 hour ago, silverton said:

quick test is to swap the AC relay with the one right next to it, which iirc is a fan relay, i'd pick the main fan vs sub fan as the sub fan should still engage with the AC button on whether the compressor is running or not. AC defaults to on in either of the windshield defrost modes, and can be turned off on face/feet. the A/C can be turned on and off no matter what temperature is selected when in face/feet mode.

Perhaps on your car. It doesn't work this way on my 05 LGT wagon.

 

[ssbtech]

1 hour ago, silverton said:

quick test is to swap the AC relay with the one right next to it, which iirc is a fan relay, i'd pick the main fan vs sub fan as the sub fan should still engage with the AC button on whether the compressor is running or not. AC defaults to on in either of the windshield defrost modes, and can be turned off on face/feet. the A/C can be turned on and off no matter what temperature is selected when in face/feet mode.

I will check the relay.  Would low refrigerant pressure detected by the pressure switch prevent the relay from being energized?  I don't know if the normally closed position of the pressure switch remains closed with low charge.  It would indicate why the relay isn't closing.  But the sub fan isn't clicking on either with the A/C light inside illuminates. 

 

 

 

 

[ssbtech]

9 minutes ago, Pleides said:

Perhaps on your car. It doesn't work this way on my 05 LGT wagon.

 

Is something wrong with yours I wonder?  I've always been able to turn the A/C on with heat to accelerate drying of the interior air.

[Pleides]

24 minutes ago, ssbtech said:

Is something wrong with yours I wonder?  I've always been able to turn the A/C on with heat to accelerate drying of the interior air.

The A/C can come on with the heat if you let auto climate control do its thing or if you use the defrost. I may be wrong but I don't think you can get the heat on full blast on just your face or feet with the A/C on in manual mode.

Edited March 30, 2023 by Pleides

[silverton]

11 hours ago, Pleides said:

Perhaps on your car. It doesn't work this way on my 05 LGT wagon.

 

That whole post sounds like an opinion piece.  full auto is just that, full auto; the car is in full control.  auto; you set the temp and the location, it handles fan speed. manual is... well.... manual.  you can do whatever the heck you want, so long as you're within the confines of the system.  that being AC is default on in defrost modes and can not be turned off, also believe fresh air is forced, you can not recirc while in either defrost modes... kinda defeats the purpose so it's nice they lock that out for the stupid people.

 

my 2001 with the levers has the same basic operating procedure as my 2017 with buttons, even so far as forcing fresh/AC in either defrost mode.

Edited March 30, 2023 by silverton

[ssbtech]

Anyway...  back to my original question   Would low refrigerant pressure measured by the switch prevent the system from turning on?  Or should I be looking elsewhere?

[Infosecdad]

3 hours ago, ssbtech said:

Anyway...  back to my original question   Would low refrigerant pressure measured by the switch prevent the system from turning on?  Or should I be looking elsewhere?

Yes.  Low pressure could cause it, as it's a failsafe to try and prevent damage to the compressor.

[ssbtech]

14 minutes ago, Infosecdad said:

Yes.  Low pressure could cause it, as it's a failsafe to try and prevent damage to the compressor.

Thank you, that's what the wiring diagram implies but I wasn't sure if low pressure with everything off would result in the pressure switch opening.  

[m sprank]

Yes.  The low pressure switch interrupts the electrical signal to the relay coil.  Standard operating procedure.  High pressure switch does the same.  You can test with a meter or by jumping the switch/relay. 

Edited March 31, 2023 by m sprank

[ssbtech]

3 hours ago, m sprank said:

Yes.  The low pressure switch interrupts the electrical signal to the relay coil.  Standard operating procedure.  High pressure switch does the same.  You can test with a meter or by jumping the switch/relay. 

Thank you - and would that also command the ECM to not turn on the sub fan?

[m sprank]

Pressure switch does not signal ecm.  But off the top of my head I dont recall the exact scenario for command.  I would need to check the fsm to verify the fan command. I believe it is tied to the compressor command. The compressor command is interrupted by the lps.