AC has me stumped

fish1534 said:

In these electric fan models, the engine fans turn on speed 1 at a set temp,
speed 2 at another temp,
and whenever the AC is on.

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latvius said:

If the AC compressor isn't running, it isn't going to turn on the fans.

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latvius said:

To the OP does it have enough freon in the system?
Like someone said start with the basics, compressor doesn't turn on
STEP 1 see if has freon.

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Marky Dissod said:

Yep.
But also, if the AC system doesn't build enough pressure, or the pressure sensor is not reporting a high enough pressure, the fans won't turn on -
even if the AC is commanded, even if the compressor is running.

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fish1534 said:

Well as many people on this board have said, it was low refrigerant. I'm amazed that was the problem because when it was at the shop for the free estimate, I asked them to check the pressures and they told me they were fine. They said they couldn't test anything more unless my engine cooling fans were spinning. I guess that I'm also amazed because I thought these were two separate systems. Electric fans were not available in my car until the year after it was made and I didn't install the efan swap until 2019. Until this time the HVAC had no control over the mechanical fan. The lesson learned is that the electric fans will not turn on if the compressor does not turn on because the low pressure sensor. The fans will still however turn on based on engine coolant temperature. Thank you everyone for the help!

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fish1534 said:

I have a 2004 and Escalade, It has the digital HVAC controls and the rear air. About 5 years ago, I upgraded from the mechanical engine fan to the electric engines fans. I used stock parts and had the computer reprogrammed, so it functions more like a 2005/2006 with the electric fans. It has worked great since 2019.

Neither the compressor or electric engine fans turn on when I engage the AC on the dash and it's hot in Florida! I can physically see that neither of the ac compressor or engine fans are on when I engage the AC so it's not a blend door or blower motor or any issue where I'm just not getting cold air to me. The compressor itself works, when I take the rely out and jumper the connection in the fuse box, the compressor turns on. I watch the compressor spin. When the engine temperature reaches 210 the electric cooling fans engage, they blow great. So both the fans and compressor work but they are not being commanded to turn on for AC. In these electric fan models, the engine fans turn on speed 1 at a set temp, speed 2 at another temp, and whenever the AC is on.

My thinking is if the gas pressures were low or the high pressure relay went out the cooling fans would still engage, that AC problems shouldn't interrupt the engine fans. It must be a signal that is not reaching both the fans and the compressor. I thought maybe it was the HVAC head unit because I have read that this is can happen so I swapped it with a junkyard model and neither the fans or compressor engage. Both HVAC head units could be bad but we are getting into lower probabilities of two being bad. I looked at the wiring harness where it connects and didn't see any broken wires. Is there a way to test the signal with the pins coming out of the HVAC head unit? Is there anyway I can put power into the harness connector to see if it engages everything?

What does everyone thing? Any clue what could be causing this? What is between the HVAC head unit and fuse box? All I know of is the engine computer. How hard is it for someone with a scanner to diagnose this? Can the ECU go bad? I had the parameters in the computer changed to add the fans but if the program reset or rebooted, the AC should still work in 2004 mode without the fans. Could I have a broken wire in the harness? Am I overlooking something simple? What shou

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