A/C help

Your high side pressure is running high. It might not be high enough to activate the high pressure switch but a constant overload for the compressor causing overheat and the thermal protection switch in the compressor to open. The engine fan blowing directly on the compressor quickly cools it to resume working.

I would also check AC compressor clutch amp draw. Anything over 7 amps should be replaced. They also overheat and work intermittently when drawing high amperage.

 

Hello bender
I have a problem with my AC, (2007 T800) causing me to suspect my compressor clutch. Both expansion valves and receiver/drier replaced by KW but did not solve the problem. Compressor will quit turning for a few minutes, come back on for a few minutes. Engine fan runs almost constant lots of times, also. Can't really give an average compressor on/off cycle time because it is not consistent; some days it has only cut off for a couple of times, coming back on in approx. 10 minutes, other days it is an almost constant cycle, staying off for different time lengths. Someone else suggested to R&r the stock compressor and install the old style, (both being the "rotary vane type", I think the difference is the newer style clutch is more problematic.)

I was intending to use a jumper wire & my multimeter to check amp pull, or is there a better way?

Thanks in advance.

 

Your AC compressor should cycle on and off to keep the evaporator in the desired cooling temp range without freezing up. Is the system maintaining cold vent temp when it's cycled off or does it blow warm air during those times? I wouldn't so much question the engine fan running a lot when sitting, parked or at slow speeds but it shouldn't normally be running at highway speeds unless certain conditions would call for it to run. I'm not sure what type of multimeter you are using but to check amp draw we generally use an inductive pickup. You can run a parasitic drain through a multimeter to check amount of draw on batteries but running that type of load through a multimeter would likely smoke it. I would do more checking of the system before I jumped to changing compressor types.

 

Check the condensor and make sure it isn't plugged(if you haven't already). Some of the symptoms you describe sound like this may be the issue.....good luck!

 

Understand about the compressor cycling on & off, when compressor cycles off, vent temps will go to ambient temp, and above quickly. Approx 6 weeks back, I picked up truck at KW after their work on the AC. Due to a late cold snap, ambient temp = 58*F; it was a Sat. morning, and shop was closed- before going into parts dept to sign ticket, I cranked my truck to let it warm up. Purchased couple of things, signed shop ticket, returned to truck where it was blowing 65*F out the vent. The last 5 or 6 miles of the 64 mile trip home, AC began cooling, pretty much the standard since.

When I mentioned the engine fan running almost all the time, I was referring to highway speeds; sometimes kicking off only to cycle on again less than a minute later. BIL's 2007 379 recently began doing similar, his problem was elect plug on radiator brace, this jarred my memory, reminding me of same problem with my 2004 W900, cause was elect plug near binary switch and receiver/drier. Will check that also.

Also, whenever I mentioned replacing compressor, I was referring to taking off the rotary vane with problematic clutch, replacing it with a rotary vane with the older style clutch. Local parts house and a mechanic both told me that if equipped with the problematic clutch, you cannot retrofit compressor with old style clutch. My compressor is a Sanden model #U4377.
This may not be my problem, I have simply run out of AC knowledge, after spending $1200.00 at local KW, I also feel they apparently over stepped their knowledge boundary. Rather than visiting, and revisiting the dealer, being able to get advise & knowledge from this forum and people like your self is alot easier on my karma, (and wallet), thanks again!

Killee Trucking, my apology for the hijack! Due to a problem similar to yours, I hope we can both gain from the gurus trying to help us.

 

droy, I would first check operating pressures to see if the system is legitimately cycling the compressor off and commanding the fan on which go hand in hand with an overcharged system. As mentioned, you could also have an airflow problem driving the high side pressure up. A simple test you can perform is to operate the AC at high idle while spraying the condenser with a water hose. If the fan doesn't run and the compressor doesn't cycle out for extended periods and the vent temp stays cold then you know that your system is sound and capable of functioning when the high side pressure is controlled.

 

I have an 2005 379 that had the same exact problems. Ended up replacing compressor and clutch - problem resolved.