HVAC Controls

interesting. I need to look at this on my 2000 1/2 ton. I finally changed out the service valves, accumulator/drier and orifice tube. Removed the old ac belt tensioner and installed a newer ac stretch belt like the 2009+. vacuumed it and started charging and it was going great. got a little over a pound into it and the clutch stopped cycling . Jumped the low and high side switches with no difference. checked all fuses and relay no difference. even swapped the head unit with no difference. still holding pressure fine. I'll check out the ground for the clutch and see if thats where my problem is. Thanks!

bigdogYJ said:

interesting. I need to look at this on my 2000 1/2 ton. I finally changed out the service valves, accumulator/drier and orifice tube. Removed the old ac belt tensioner and installed a newer ac stretch belt like the 2009+. vacuumed it and started charging and it was going great. got a little over a pound into it and the clutch stopped cycling . Jumped the low and high side switches with no difference. checked all fuses and relay no difference. even swapped the head unit with no difference. still holding pressure fine. I'll check out the ground for the clutch and see if thats where my problem is. Thanks!

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For what it's worth, I find it helpful to troubleshoot at the relay in the fuse box under the hood. Locate the AC compressor clutch relay and remove it. It should be a 4 pin relay. I can't recall if the 2000 is the same as the later trucks, so I would verify the wiring. But on my 04 they are labeled 87, 86, 85, and 30. 30 is constant power, 86 is switched power (ignition), 85 is ground (from PCM and triggered by AC button on dash), and 87 is output to the AC clutch.

Jumping 30 and 87 you can then check the wiring from the fuse box to the clutch. You should get 12v at the plug. Grab the frame with a test light first and verify 12v on the positive side of the plug. Then verify the ground in the plug is working. If that checks out, it is in the triggering somewhere.

Since the AC button/PCM trigger the ground on the relay, you can check that too. I jump the low-side sensor, start the vehicle, and switch the AC on. You should get a ground on pin 85 of the relay. I use a test light and pin 30 for my 12v source. Again, verify the early gmt800 wiring is the same as the later trucks before trying this. Hope this can help you get some cool air!

Moved to another thread. Sorry for hijack. Was not meant and was not paying attention.

Moved to another thread. Sorry for hijack. Was not meant and was not paying attention.

Moved to another thread. Sorry for hijack. Was not meant and was not paying attention.

Moved to another thread. Sorry for hijack. Was not meant and was not paying attention.

Moved to another thread. Sorry for hijack. Was not meant and was not paying attention.

INW-Iron-Steel said:

I've been searching Ebay for years now! I know that sounds like a stretch, but from time to time I will find all the OE part numbers and just throw them in an Ebay search, but I haven't found anything good yet. Just a bunch of new no-name generic garbage. Good suggestion on the blend door actuators, I'll make sure those aren't faulty too. They are all noisy, I can hear them when I move a knob or adjust the slider. I am really thinking the issue lies in the control, but I could be completely wrong. Seems like something is internally shorted specifically on the AC circuit somewhere. I don't have issues adjusting the fan or temperature when it is cold out and I need heat.

So, I guess the search for an OE piece continues. Not really a bad thing, just means the wife won't want to take my rig when the weather gets hot.

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I have an issues with the firewall insulation rubber drying out and breaking off and actually crumbling and interfering with the actuator motors, creating a whining and crunching sound resulting in the system going to. Default on constant defrost. Be aware, if you go to O'Reilly's for a MODE actuator, they will sell you a blend door. I learned this
by calling doman directly .if it's a plastic gear, it's not a mode, but a blend door.

bigdogYJ said:

Removed the old ac belt tensioner and installed a newer ac stretch belt like the 2009+.

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I was watching a YT video yesterday and the guy mentioned this retro-upgrade. I was not aware of this.


Around the 10 minute mark. I will try it next time I have to replace an AC belt or tensioner on one of my trucks.

Edit: my buddy just told me you can also retro-upgrade to the newer style air compressor too?! Apparently that makes for more room when installing a turbo kit...

stutaeng said:

Around the 10 minute mark. I will try it next time I have to replace an AC belt or tensioner on one of my trucks.

Edit: my buddy just told me you can also retro-upgrade to the newer style air compressor too?! Apparently that makes for more room when installing a turbo kit...

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Good to know on the newer style compressors! I am a big fan of the stretch belt. Keep in mind they are one time use. I learned that the hard way

INW-Iron-Steel said:

Good to know on the newer style compressors! I am a big fan of the stretch belt. Keep in mind they are one time use. I learned that the hard way

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Good to know. I was wondering how one would remove those...I guess just cut it out?

I was talking to my brother that did a 6.0 LS swap on his 90 RCSB C1500. He used some aftermarket bracket to mount his original style AC compressor. He says he feels some vibrations inside the cab when the compressor kicks on and gets annoying. I was telling him that maybe GM had designed the AC compressor on the LS engines with it's on belt and tensioner to help with vibrations? Just me speculating, because apparently they didn't feel like they needed the tensioner anymore? Who knows?

stutaeng said:

Good to know. I was wondering how one would remove those...I guess just cut it out?

I was talking to my brother that did a 6.0 LS swap on his 90 RCSB C1500. He used some aftermarket bracket to mount his original style AC compressor. He says he feels some vibrations inside the cab when the compressor kicks on and gets annoying. I was telling him that maybe GM had designed the AC compressor on the LS engines with it's on belt and tensioner to help with vibrations? Just me speculating, because apparently they didn't feel like they needed the tensioner anymore? Who knows? View attachment 6166

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The aftermarket bracket likely wasn’t a tuned aluminum bracket like the oem either. That’ll transfer vibration too

stutaeng said:

Good to know. I was wondering how one would remove those...I guess just cut it out?

I was talking to my brother that did a 6.0 LS swap on his 90 RCSB C1500. He used some aftermarket bracket to mount his original style AC compressor. He says he feels some vibrations inside the cab when the compressor kicks on and gets annoying. I was telling him that maybe GM had designed the AC compressor on the LS engines with it's on belt and tensioner to help with vibrations? Just me speculating, because apparently they didn't feel like they needed the tensioner anymore? Who knows? View attachment 6166

Click to expand...

I think the own belt was to package the engine tightly, but keeping the ac cycling off the main belt was definitely designed into the regular serpentine and tensioner so adding to that would exceed the factory design that way