'06 Mega Cummins; I just replaced the AC compressor (5th one), also installed a new condenser, orifice, dryer, pressure transducer, evaporator is only 2 years old, flushed the lines, measured and weighed the oil, evacuated for an hour, charged the exact amount and its barely cool. The fan runs. The compressor kicks in for 10 seconds and then off for 5 seconds; off and on, off and on, What causes it to cycle off & on? Thanks for comments.

 

Still low on charge.

 

When you say evacuated for an hour, did you put it under a vacuum and it held? Also is your condenser fan running when you kick the A/C on?

 

Yeah, vacuumed and it held. The condensor fan does run when AC turns on. I'm reluctant to overcharge it, but may do it just to rule out that possibility. Thanks for info.

 

Yeah, then it sounds like you're low on charge, but not ridiculously low since the compressor is cycling. I can't believe you're on the 6th compressor, I still have my original in my 03. That's nuts.

 

I've read the numerous posts about the pitiful AC systems in these trucks and I've lived every one of the headaches. Removed the dash 3 times (I've got it down to about an hour out and an hour in) replaced blend doors several times. So now when I have a problem, I just go ahead and replace everything I can with new. But I never experienced the cycle on and off before. I guess I'll charge a few more ounces and see how she responds.
Thanks for your input!

 

Put gauges on it, and see what they have to say. My guess is, low side pressure isn't going to be up to spec.

 

The low pressure side builds up to about 100 and at the same time the high pressure drops to 150ish. Then the compressor cycles and the low drops to 30-40 and the high increases to 250-300. Its hard to get a steady reading when its on/off every 10 seconds.............. I'm wondering if there is some internal computer controls that is overriding the system somehow.... I don't know how, or if, that computer system effects this process.
I even considered going to the stealership. Called them and they said they could work me in in 6 days. Service guy said they get about 150 cars a day into their service dept. Thats not a stat I would share, its not exactly a point of pride for the brand.
Thanks for comments

 

That's funny; A/C in my truck will turn it into a meat locker in 10min lol. It's the best A/C I've ever had. Never had an issue except the fan going on it and the recirc door breaking (has over 150,000 on it, so I'm not complaining).

 

Wonder if the system is over-charged already...... what was ambient temp when you were getting those pressures?