A/C Gremlins

Discussion on Air Conditioning/Heat & electronic controls for the same, radiators/fans/engine cooling and related items.
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BluesBro
Posts: 108
Joined: Tue Aug 03, 2021 6:26 am

A/C Gremlins

Post by BluesBro » Wed Jun 22, 2022 1:48 am

Interesting issue(s) popped up this weekend. A/C stopped blowing cold air along with some other interesting things. It rained this weekend and I drove quite a while in the rain, normally I wouldn't think twice about this but it seemed to line up with the following events. Compressor would no longer engage, pressures were fine. DIC indicated "Ice Possible" and HVAC flashed ambient temp of -40*F, it was around 65*F in reality. The last strange thing was that the desired HVAC temp on the screen has always been in Celsius while the knobs display in Fahrenheit, when all of this happened the desired HVAC temp on the screen changed to Fahrenheit.

I made an appointment with my A/C shop because I figured the compressor died and I don't have time to change it or the ability to evacuate/fill the system.

Today, the desired HVAC temp was back displaying in Celsius, I tried the A/C, and ice cold.

Is there some sort of cold weather override on the A/C allowing the malfunctioning ambient temp sensor to stop the compressor from engaging? Are these events uncorrelated malfunctions that all happened to be cause by moisture?
2014 Caprice PPV 6.0L - TSP Stage 1 Cam, Solo 3in Mach Cat Back, VCM OTR, HP Tuned
2002 Avalanche 5.3L - MBRP Exhaust, RC 6in Lift

JoeR
Posts: 52
Joined: Wed May 25, 2022 5:34 am

Re: A/C Gremlins

Post by JoeR » Wed Jun 22, 2022 3:05 am

You're correct. Ambient temp sensor needs to read over 34 degrees F for the compressor to work.
If the wiring goes open (disconnected) it will read -35 or so like you saw. Play with the wiring to see if you can find something. Keep in mind the message on the dash doesn't update quickly, so you're probably going to need a multimeter of you don't spot something obvious.
Joe

BluesBro
Posts: 108
Joined: Tue Aug 03, 2021 6:26 am

Re: A/C Gremlins

Post by BluesBro » Wed Jun 22, 2022 3:12 am

Here is the next question, where is the ambient temp sensor? Diagrams I was looking at show it in the radiator support but I cannot find it on my car or the other 2014 we have that has the engine and radiator out.
2014 Caprice PPV 6.0L - TSP Stage 1 Cam, Solo 3in Mach Cat Back, VCM OTR, HP Tuned
2002 Avalanche 5.3L - MBRP Exhaust, RC 6in Lift

JoeR
Posts: 52
Joined: Wed May 25, 2022 5:34 am

Re: A/C Gremlins

Post by JoeR » Wed Jun 22, 2022 3:45 am

Dunno, but they are always located forward of the condenser. Mitchell Repair shows it on the right side of the radiator support very near the radiator opening.
Here's what it looks like: https://www.gmpartsdirect.com/oem-parts ... s-25775833

BluesBro
Posts: 108
Joined: Tue Aug 03, 2021 6:26 am

Re: A/C Gremlins

Post by BluesBro » Sat Jun 25, 2022 3:07 am

The saga continues....

A/C worked fine for a few days after the car dried out. Today I took a close look at the black caprice with the engine and radiator out looking for the ambient temp sensor. finally found it tucked behind the headlight, tangled up with the police flasher wiring. After finding it, it became clear where it was supposed to go. It was on the passenger side in front of the condenser, between the washer bottle and headlight.

Back to my car with sensor in hand, found the connector unplugged. Found a sensor in the radiator support but the connector was different, probably a leftover from the donor car that was used for the front clip replacement. Plugged the good sensor in from the black car, A/C stops working and -40* is displayed on the screen. Damnit. I began troubleshooting the wiring, 5.00V at the connector, 0.00 Ohms to ground, 0.00 Ohms across connector. Sensor tests good at 8.3K Ohm. Plug the sensor in, back probe connector and get the appropriate voltage drop. Still -40*.

I start thinking the car may need to relearn the sensor, so I disconnect the battery and let it sit. When I fire it back up A/C works, -40* is gone. I think I am done but I shut it off and start it again to validate the repair, and -40* again. Damnit. I then decide to just put a 500 Ohm resistor across the connector to check, same behavior. I then put a wire across the connector, same behavior. I unplug the sensor, disconnect battery, and A/C works again...what the hell. I validate by starting the car 4 times, still works. So this is where I leave it for now, I guess. It should read -40* with the connector open but it does not.
2014 Caprice PPV 6.0L - TSP Stage 1 Cam, Solo 3in Mach Cat Back, VCM OTR, HP Tuned
2002 Avalanche 5.3L - MBRP Exhaust, RC 6in Lift

BluesBro
Posts: 108
Joined: Tue Aug 03, 2021 6:26 am

Re: A/C Gremlins

Post by BluesBro » Sat Jun 25, 2022 5:42 am

This is also puzzling.

When the A/C functions, which has been most of the time for the last year, the temp is displayed in C


When it is malfunctioning it displays in F


Does anyone else have their display in C? I have been unable to find a place in the settings to change this manually.
Attachments
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F_resize.JPG (128.49 KiB) Viewed 88 times
C_resize.JPG
C_resize.JPG (130.86 KiB) Viewed 88 times
2014 Caprice PPV 6.0L - TSP Stage 1 Cam, Solo 3in Mach Cat Back, VCM OTR, HP Tuned
2002 Avalanche 5.3L - MBRP Exhaust, RC 6in Lift

JoeR
Posts: 52
Joined: Wed May 25, 2022 5:34 am

Re: A/C Gremlins

Post by JoeR » Sat Jun 25, 2022 2:33 pm

This is going to be tough to diagnose without a good scanner. The ambient temp sensor is wired to the instrument cluster. It must get into the HVAC Module on the data bus, because there's no hard wired connection. So as a tech, my next move would be to see what the ambient temp sensor is reading at the instrument cluster when the signal goes bad at the AC module.
It would also be good to see if you have U codes in the cluster or HVAC modules. Maybe the data bus is dropping out.
Lots of "maybes" until you can see what the computers are doing.
Joe

Sanford
Posts: 250
Joined: Tue Dec 13, 2016 3:38 am
Location: Texas Gulf Coast

Re: A/C Gremlins

Post by Sanford » Sat Jun 25, 2022 10:34 pm

A good scanner is a must for working on these things. You will guess yourself into the funny farm without the live data.

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