AC operation.... can an actuator prevent AC?

[budwich]

My AC quit yesterday on my 2008 TB with auto controls. The "snowflake" was lit and fan going but no AC. Of course, no compressor activity as torque showed no changes in the AC pressure (normally functions well). I did a quick check of the GM SI for fuse locations ... two in the rear fuse block (SI indicates 38, 39, but vehicle box indicates 36,39... both 10A). Anyway pulled both, put back one (39 I think), still no display (somewhat expected) but there was a bit of noise somewhere up front (relay like maybe). Put back 36, display appears and looks "normal" (like it always is). Start the vehicle and got cooling again...yippy!!! Monitor with torque shows "normal" pressuring.

I suspect a faulty actuator might have caused the issue as they are all original on a 260kkm vehicle. Hence, the question: can an actuator cause the AC to not operate / energize the compressor? Seems a bit of a "stretched" but just wondering. I am going to monitor things a bit closer to see what's up. The compressor /drier were replaced about 3.5 years ago by garage (old compressor had a clutch issue).

I guess that perhaps a "poor fuse conn" could cause issues with temperature readings of the control such that the unit "thinks" no AC is required maybe (although the setting on display did indicate my temp request of 18C) or possibly the internal cabin temp sensor was saying it was below 60F? I don't know what that reading was / is as torque doesn't have a pid for that (as far I know). Comments?

 

[Mooseman]

A couple of things to try. Pull the connector on the low pressure switch and jump it. If it starts, then your system is likely low. If that doesn't work, try jumping the relay. If it then starts, try swapping it with another. If no dice, check to see if the PCM is sending the signal to the relay and that power is getting to it (can't remember if it's + or -, check the schematics)

 

[Joe_67]

Did you double check on the torque app reading by opening the hood and looking at the compressor clutch to see if it was spinning? Did the accumulator and lines get cold and sweat a lot at the time?

A faulty actuator can't cause the A/C system itself to malfunction, but it can keep the cold air out and the hot air in. That's just the blend door. The actuators are just about controlling air flow, but won't affect whether the truck can make hot air vs cold air.

Do you have a code reader that will read anything other than generic OBDII codes?

 

[Mooseman]

He did say that there was no compressor activity. He did reset the system so the module may have been at fault or is possibly low, letting it work minimally.

Please reads posts prior to posting snarky comments.

 

[Joe_67]

He did say that there was no compressor activity. He did reset the system so the module may have been at fault or is possibly low, letting it work minimally.

Please reads posts prior to posting snarky comments.

I edited to remove what I'll take to be snark.

I read the posts and all I was saying was that it seemed like the OP was relying exclusively on a torque app (presumably torque pro) to judge what was happening with refrigerant pressures. I merely suggested a quick and more direct way of verifying compressor activity.

I was genuinely asking and looking to help.

 

[budwich]

Thanks... no problem either way. The purpose of my torque app was to confirm some form of "compress action" as I do monitor regularly and am aware of the readings when the compressor is working and when it isn't. I continue to monitor things and its operation is regular again without incidence. Pressures level at both "compressing" and not are in regular range for the outside temps (24-28C). At this point, I suspect possibly a bad fuse position in the rear box. Looking thru the GM SI, I see no mention of any actuator position "protection" or otherwise to stop the system.... but maybe the interior air temp sensor might be fubarred and cause something.... more reading around that operation.

 

[Joe_67]

Thanks... no problem either way. The purpose of my torque app was to confirm some form of "compress action" as I do monitor regularly and am aware of the readings when the compressor is working and when it isn't. I continue to monitor things and its operation is regular again without incidence. Pressures level at both "compressing" and not are in regular range for the outside temps (24-28C). At this point, I suspect possibly a bad fuse position in the rear box. Looking thru the GM SI, I see no mention of any actuator position "protection" or otherwise to stop the system.... but maybe the interior air temp sensor might be fubarred and cause something.... more reading around that operation.

I unfortunately can't offer any help with the technical specs /testing info on the interior temp sensor. But if does get fubarred (whether the sensor itself or comm with the module) it can certainly make a mess of the auto system functions. So perhaps someone else can offer better tech info on testing procedures.

I'm not familiar with the torque app, but I know the full version can be pretty powerful. Does it pull GM body codes, and did you scan for codes? I'd start there if you haven't.

I'd also wonder about the low pressure switch as suggested by Mooseman. You could have a little leak leaving you low at times. Or that switch can also go bad, but not necessarily all at once - so it can be intermittent. If you can "catch" the system in failure mode it is as easy as pulling the plug and jumpering the wire directly. A paperclip works just fine for that. If it does, by chance, fire the compressor, don't leave it running until the refrigerant levels are checked by gauge as you don't want to fry your compressor just in case the torque app is off for some reason.

And I know you said that the compressor/clutch were replaced, but it's not to hard to check for problems, and the clutch can also be intermittent. Measuring the air gap is quick and easy if you have a set of feeler gauges (which are cheap if you don't). And if it's in failure mode again, and you're even slightly handy and have a multimeter, you can back probe the red wire on the compressor and check to see if it has voltage. It shouldn't be in bad shape after only a few years, but if they were aftermarket/rebuilt parts who knows? If the compressor in inoperable but has voltage present then you're looking at a clutch problem.

 

[budwich]

Thanks. I was somewhat lazy on the troubleshoot effort. I started with the SI, then which gave me fuse info and checked those first. IF it goes again, I will likely get the low pressure switch first and then go from there.

The torque app doesn't do body codes and I never even thought of just scanning for codes in the first place (not thinking) since there was no light,,,duh!... that's a check engine light and the problem ain't an engine issue... I was fighting other issues around the house, and time was not really there to follow a "good analysis"... more like get it working and worry about it later.

The truck hasn't been used for very many long periods lately so the AC really hasn't gotten a workout so I haven't ruled out much quite yet.

 

[Mooseman]

Car Gauge Pro does do body codes, as well as ABS and SRS, in case you need it. Or come by and I'll hook up my Tech 2