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A/c help

2K views 24 replies 5 participants last post by  cart7881 
#1 ·
New to Colorodo life. A/C was working good. I just bought truck. LSA swap, cleaning up some wiring .
And now my a/c won’t kick on? I tryed testing the fuses? Good, relay good. Jumped relay and A/C kicks on? So does that mean my HVAC control is bad?? Ho do I test?
 
#2 ·
Okay, what you know. The compressor will operate. The A/C relay is good. Bypassing the relay will cause the compressor to operate. If the A/C was working good before you 'cleaned up' the wiring, maybe recheck that wiring.

You are missing either the power supply for the relay, which is the 15A IGN fuse, or the ground for the relay which is in the PCM.

The way the system works is that the HVAC Conrol Module sends a voltage signal to the BCM requesting compressor operation. The BCM looks at the evaporator temperature and if it is above freezing sends a Class 2 Serial Data message to the PCM to turn on the compressor. The PCM looks at engine coolant temp, engine speed and A/C system pressure. If good, the PCM grounds the control circuit for the compressor relay.

Bottom line. If you have power from the IGN fuse to the relay and you are certain the relay is good, there is either a wiring problem between the fuse box and the PCM, or an issue with the PCM. Unless the BCM and HVAC Module were mucked with during the swap, the problem is most likely somewhere in the engine compartment. Either a high system presssure or a low system pressure will prevent the compressor from operating.
 
#4 ·
Under the instrument panel, forward of the glove box, look for a connector mounted to the face of the A/C case. Black connector, 10 wires. Disconnect and probe the terminal for the Green wire with a White stripe in the male half of the connector. Meter or test light. Find a good ground in the area. With the key on and A/C selected you should get 10-12 volts.

That's the circuit from the HVAC Module logic board to the BCM. There is no direct connection from the switch. This is because the switch is not the only way the compressor operates. It will automatically turn on if the mode select knob is turned to defrost and then the light in the switch will not illuminate.
 
#9 ·
I do not usually inject myself into Carrt's postings but Ihave a question on your AC. When you press the AC button and the fan is on, Is the AC light illuminated (on) inside the AC button? It the answer is "yes" then when the fan switch is turned all the way counter clockwise does the fan stop and the AC light go "OFF". It is the light going off that I am really questioning. If the answer is "NO" the light stays on, then you have a bad dround connection probably in the splice pack mounted behnd the air cleaner on the passenger side inside fender. I have seen this problem severakl times. If it did go off from turning the fan switch (not pressing the AC button), then you can ignre this entire posting.
 
#11 ·
Thank you for the post. The more 'eyes' there are on the problem, the more likely that a solution will be found. One person posting can easily overlook obvious clues sometimes. The only advantage that I have is access to the Service Manuals and the past history on this site. Before I joined here I took the time to read every single post from the beginning. That was in 2011 and it took me a couple of months. Learned a lot.
 
#10 ·
I’m interested in getting this figured out. When I push the switch in, I get nothing? No light?
I did a lot of wire clean up by the mass air / passanger side of truck.

I seen a video of a guy testing the a/c havac system by pulling relay, and and testing the A/C clutch enhancement button.
 
#16 ·
It’s no telling.. I’m sad, I bought this fruck, but she’s mine.. and I’ll get it figured out. I’m very picky about wiring. I solder everything. This truck is built on clip on wire taps. 😤

don’t ask what I had to pay..

Now we got that out of the way… anyone rode in a Boosted 4x4 6.2l Colorodo lately?? AND I SMILE JUST THINKING ABOUT IT.
 
#21 ·
Update..I was driving truck to my toolbox , transmission started acting weird?? Parked, and trailers to shop. WAITING FOR Diagnosis.
Im learning learning lil by little..scared OB2, nothing,

Hp tuners is incorporated into the trucks PCM. So hopefully we can track the Transmission problem. Then I’ll return to A/C.
 
#25 ·
Update..I was driving truck to my toolbox , transmission started acting weird?? Parked, and trailers to shop. WAITING FOR Diagnosis.
Im learning learning lil by little..scared OB2, nothing,

Hp tuners is incorporated into the trucks PCM. So hopefully we can track the Transmission problem. Then I’ll return to A/C.
Regarding the A/C. I'm still not clear on how and when this issue started. From the first post I assume that the truck has a swapped engine. I also asume that when the truck was purchased, with the swapped engine, that the A/C was operating normally. Then, after you "cleaned up" some wiring, the A/C would not operate. Are those assumptions accurate? If so, are you convinced that something you "cleaned up" didn't contribute to the problem?
 
#22 ·
Back on Mar 9th I posted in this because of your comment of when I press the AC button the light will not turn on. I hope you saw it, but you just never replied. That light is turned on ONLY when the fan is in position one or higher,,. NOT in the lowest OFF position. The light is controlled right there in the HVAC module by the blower switch along with the AC switch . To turn it off, the lead from the fan switch off position to the logic portion of the HVAC module is grounded (-12 volts DC). The absence of the light on tells me that either the bulb is bad, you have the fan switch in the off position, the blower motor switch is bad (probably shorted) or that lead is grounded by the HVAC control module.

The lead leaves the blower switch on pin A of the HVAC module, and runs on a dark green wire that returns to the logic portion of the HVAC module on PIN 7 labeled on the schematic "OFF BLW MTR CONTROL". With that line grounded, the HVAC module is never going to tell the BCM to turn on the compressor.

So until you can get that light to turn on and off correctly, nothing else you check is going to work to fix your problem.

If you do end up replacing the module, be careful. I got one from an 06 to put in an 05 and they were different. I ended up robbing the switch out of the 06 module and putting it in the original 05 HVAC module.

Good Luck
 
#24 ·
Back on Mar 9th I posted in this because of your comment of when I press the AC button the light will not turn on. I hope you saw it, but you just never replied. That light is turned on ONLY when the fan is in position one or higher,,. NOT in the lowest OFF position. The light is controlled right there in the HVAC module by the blower switch along with the AC switch . To turn it off, the lead from the fan switch off position to the logic portion of the HVAC module is grounded (-12 volts DC). The absence of the light on tells me that either the bulb is bad, you have the fan switch in the off position, the blower motor switch is bad (probably shorted) or that lead is grounded by the HVAC control module.

The lead leaves the blower switch on pin A of the HVAC module, and runs on a dark green wire that returns to the logic portion of the HVAC module on PIN 7 labeled on the schematic "OFF BLW MTR CONTROL". With that line grounded, the HVAC module is never going to tell the BCM to turn on the compressor.

So until you can get that light to turn on and off correctly, nothing else you check is going to work to fix your problem.

If you do end up replacing the module, be careful. I got one from an 06 to put in an 05 and they were different. I ended up robbing the switch out of the 06 module and putting it in the original 05 HVAC module.

Good Luck
I seen your comment, I went out to start testing, I have no light engagement switch on?? Doesn’t matter where the fan switch is on ??
I’m hoping to find out something on transmission. Need my truck back.

I got myself into a mess
 
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