AC has me stumped

[Marky Dissod]

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.

Yes, Yes, and ... NO.
There are AC pressure sensors in the AC system that report to the pcm.
These are the GM OE psi threshold settings for an '05 Silverado
Lo Speed Fan-ON Threshold is 220psi , OFF Threshold is 150psi.
Hi Speed Fan-ON Threshold is 310psi , OFF Threshold is 230psi.

Doesn't matter if the AC is requested, or ON, what matters is the pressures the pcm sees.

 

[latvius]

To the OP does it have enough freon in the system? Your compressor isn't going to turn on if it doesn't so jumping it to see if it works isn't the best idea.
Like someone said start with the basics, compressor doesn't turn on
STEP 1 see if has freon.
This whole discussion about electric fans and when they come on is a sideshow. If the a/c compressor isn't running it isn't going to turn on the fans.

 

[Marky Dissod]

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

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.

 

[ivin74]

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.

X2^

 

[latvius]

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.

Yeah that is good info except his compressor isn't running...

 

[rockola1971]

My bet is OP has a leak and the LP cutoff switch is not allowing the PCM to get enable signal which is ultimately what allows the PCM to send out coil signal for the control relay for the A/C clutch so the clutch not engaging. OP needs to get gauges on the low side and report what it is showing. (Youll need r134a gauges) The low pressure cutoff is around 28PSI. If pressure is below the low pressure cutoff rating then the A/C clutch will never engage and the system is setup like by design. It prevents the compressor from running with very low or no pressure. The compressor doesnt like running with no lube oil cycling through it and that lube oil is mixed with your refrigerant.

 

[fish1534]

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!

 

[Doubeleive]

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!

now you just need to find the leak..................

 

[CraftyCrafts]

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

 

[houstontaylor]

I had a problem with the fuses for the inside AC control unit on my 2003 Tahoe. Even though the fuses looked perfectly fine I believe the aluminum legs of the fuses were oxidized over time and the fuses were not working. Oxidized aluminum is non-conducting. When I replaced them the air conditioning controls worked fine. I believe there is one fuse on the driver side of the dash and another under the hood that affects that control unit. Something to look into anyway.