'94 Suburban A/C works, but intermittently

chevrolet
suburban
airconditioning

#1

This is a 1994 Chevy suburban C1500 with the gas 350 v8, 2wd, with front and rear a/c units. Entire A/C system, including compressor, evaps, condensor, hoses, accumulator, the whole smash was rebuilt with new components by an a/c specialist 2 years ago.



Now, for some reason occasionally the system does not want to turn on even though the system is switched on. This morning I went out to check things out to see what I could find.



I started the engine, and turned the system on HI with coldest possible temp setting and set blower to HI. Nothing. System did not come on. Well, after about 4 minutes, while I was checking various things, lo and behold the compressor clutch engages and the system comes on. The system kept running steady for several more minutes while I hooked up my guages. Lo side read 45 psi, hi side read 190 psi, outside temp was 72 degrees.



I checked the air vents, and the system was blowing nice and cold. I drove the truck around for a few minutes, and I just about froze. I stopped and shut the engine and a/c system off, and keft them off for about 20 minutes.



I started the engine and the a/c system again, and this time it was about 30 seconds after I switched the system on before the a/c compressor clutch engaged. But once it was on it ran fine.



One other thing I have noticed previously is, when the syetm is running on LO, the compressor will cycle on and off very fast. It sounds similar to a frayed belt hitting something when it does that (but belt is fine). The remedy for that is to turn the system to HI so it runs continuously, and then it is fine and does not cycle on and off like that.



I am going to check the electrical connections at the compressor to make sure they are clean and tight. Any other ideas for what I should check?



Thanks!



Pop


#2

I suggest you check the power supply lead to the compressor clutch first. It sounds like there is a bad connection to it.


#3

OK will do thx.


#4

I detect two things from the information you provide and they don’t fit together. Your low side is not low enough and you report rapid clutch cycling. This rapid cycling usualy comes with a low charge and the low charge is usually evident with abnormaly low low side pressures.

Making sure the magnet at the clutch is correctly supplied with voltage is a very good thing to verify (along with the air cap) and you do need to get your low side cycling between 28-38. Follow the performance testing chart in the FSM, the older manuals call for a fan blowing accross the condensor, the newer ones don’t call for the use of a fan.


#5

Cleaned clutch switch connection. Didn’t seem too dirty, but system comes on more reliably now. The only time it fails to come on now is when I forget to turn the a/c off before turning the engine off. When that happens, I just switch the a/c off then engine, then restart engine then switch on a/c. That is kind of goofy, but it works and I cann live with it.


#6

Well, now that it is getting warm again, I thought I’d revisit this problem. This is all the more necessary because the system will not come on at all now. I think it has to ddo wiith the switcch that is mounted to the acccumulator. When I push on that switch, the ccompressor will ccome on. Here is a video of what is going on. Any inpput is appreciated! http://www.youtube.com/watch?v=1GsT0SFdow8


#7

The AC system doesn't need to be discharged in order to replace that low pressure switch. The accumulator has a Schrader valve where the switch is mounted so when the switch is removed the Schrader valve closes and prevents the escape of refrigerant.

Tester


#8

Thanks, Tester! Replaced switch, and system is cooling very nicely now.

~Pop