BillyNilly

Hello everyone:

My 01 Tahoe's AC compressor will cut off and not cycle again after sitting still at a light / drive thru, or when RPMs or speed have been low for an extended time (driving in town, for example). Until recently, turning it off for about 5 - 10 mins would fix the issue. However, now it's gone off and will not come back on.

When the compressor does cycle, the air is very cold and the AC works as expected.

Troubleshooting that we have done:

• Replaced Orifice Tube (old tube was clean with no debris)
• Replaced Radiator Fan clutch
• Replaced Low Pres. Cycle Switch
• Pulled vacuum and held for 30 min, refilled system to factory specs with R134a
• Replaced Ambient air temp sensor located in front of condenser
• Replaced AC Belt and tensioner (probably not related but belt was worn upon initial inspection)
• Sprayed out condenser with low pressure water to clean the fins a bit (externally only)

My next suspect is A/C clutch, which we will check tonight for voltage. We have also swapped relays in the fuse box with no change. We have verified that the system is still charged and is not leaking (used manifold gauges). Cycle pressures appear normal as well when the compressor is/was running. It had been working intermittently but suddenly stopped altogether and now is not coming on at all. Also worthy to note that when jumped at the low press switch connector, the compressor does not come on.

What are we missing besides the obvious? Hi press switch will be next after we check the AC clutch. Are there any other sensors that could cause the AC clutch not to cycle?

Also, to what extent can the head unit be responsible for this? The AC light does not go off when the compressor stops cycling. Is there a way to test the head unit without pulling it out?

Pulling out hair here - any help is appreciated.

BillyNilly

UPDATE:

On a whim, I re-seated the A/C relay and the 10a AC fuse in the fuse box and disconnected / reconnected the cycle switch connector. After doing this, the compressor came to life for the first time in 2 days. It lasted through a sit at a drive thru and then cut off again while driving through town. However this time, it came back on after only about 2 mins. Stayed on for another few mins, and back off again.

I noticed that the A/C relay was REALLY hot to the touch when I pulled it. Is that an indicator of a short somewhere or is that normal? I could barely touch it.

jfmorris

Maybe replace the relay? They should not get that hot unless there is arcing at the relay contacts or it is opening/closing a lot. That said... I've not felt the relay during operation on my old 2003 5.3L or the 2006 4.8L. I may check it during operation later today and let you know if the relay runs hot to the touch.

BillyNilly

Thanks for the reply - I forgot to mention that we swapped the relays in the fuse box but there was no change prior to the fluke yesterday. The only thing I did that we didn't try before was removing and re-seating the 10a AC fuse as well as swapping the relays. Will try a new relay next.

jfmorris

If you swapped relays I doubt a new one is going to fix the issue. I am going to suggest a couple of other things to check.

First - if the coils are dirty - especially the evaporator coils (the ones under the dash), or a cabin air filter is extremely dirty, it can reduce the performance, and cause cycling of the compressor clutch, due to pressure build ups. This could also happen if the condenser coils are dirty.

On my wife's Subaru, if I don't change the cabin air filter annually, she really notices a hit in AC performance, and the compressor cycles on/off more often than normal. With that in mind, I went digging into my 1996 C1500, and 2006 Silverado, neither of which have a cabin air filter. I had to remove the blower motor, but was able to partially access the evaporator coils in the air handler under the dash, and found that the fins on the coils of the 1996 especially were almost 100% clogged up with dust and debris. I sprayed coil cleaner back into the opening with the blower removed, let it work for a few minutes, then used a garden hose nozzle to spray the coils off. You would not believe how much filthy water ran out the condensation drain on the firewall, and onto my driveway. It also made a huge difference between a barely working AC, and one that was blowing 40-something degree air.

Another thing that could be a factor - you replaces the expansion tube, but any blockages in the condenser could impact performance. May be worth considering replacing the condenser (in front of radiator) and accumulator (by the firewall) if you haven't already. That pretty much would eliminate all but the evaporator coil under the dash (very difficult and time consuming to replace) and the compressor (easy to replace).

You could also be looking at faulty pressure switches. I would watch it with high/low side gauges hooked up to see if the pressures are running higher (or lower) right before the compressor cycles off. I would START with that test.