Hey all-

I was having problems with my compressor not turning on at all when I put the A/C on. I was following the steps in the repair manual to test various parts of the system.

When I jumped the clutch cycle switch, I did not hear the compressor relay click on but the engine would noticeably change in pitch, suggesting that something was loading the engine. I didn't know what to make of this so I moved on.

In trying to test the resistance between the pins on the high pressure cutoff switch, I think I accidentally jumped them. Now the compressor does come on (and colder air comes out in the cabin) but it shuts on and off. If I disconnect the high pressure switch completely, the compressor does not turn on at all when the A/C is turned on from the cabin.

Anyone know if I fried something? Now, after doing more reading, it looks like I should have started by replacing the cycle switch. Should I replace the high pressure switch? Or are my problems much bigger now?

Also, it's the 4.6L V8

Thanks,

-Ed

 

Well first thing you need to do is get a gauge on the system and check your R-134 level. If you have a leak and the R-134 is low then your compressor will short cycle(click on and off in short cycles)

Also if you are jumping the system to get the clutch to engage you will be able to hear it as all it is is a metal plate being attracted to a magnet you there will be an audible noise when the compressor comes on. IIRC the low pressure switch is what tells the compressor to not run when the R-134 is low. So what you will need to do is bypass that switch to see if you can get the compressor to come on. If you can you might want to go to the parts store and pick up a can or two of R-134, hook it to the low side port, turn the ac system on and add some r-134 to the system. You will need to get the compressor to kick on a few seconds at a time to suck in the R-134. Once it gets enough it should be able to cycle itself to pull in the rest of what it needs.

 

Ok, so before seeing the response to my post, I went out and bought both the compressor cycle switch and the high pressure cutoff switch and replaced each. The issue remained the same with the quick on/off cycle but I added refrigerant as suggested and now the AC works normally (and of course it's nice and cold!).

As far as what originally was causing the compressor not the come on, I'm not sure. Maybe a blockage that accidentally jumping the high pressure cutoff (luckily) cleared out instead of blowing something up?

Anyway, the problem is fixed, thanks for the help!

-Ed

 

Glad you got it working.

Just a thought, did the a/c system give you any indication that there was a problem before the compressor started to short cycle? For example was the a/c not cold or did you notice it got warmer when stopped ideling vs. driving?

Reason I ask is for a 98 it could have just needed a charge, but if that was the case it would have been giving signs of being low. If it went from working normally one day to the compressor short cycling in a matter of days chances are you have a leak and the problem will come back, and back, and back until you get the leak fixed.

 

I think it was working fine, but I really don't know. I hadn't been driving the truck regularly at all, just enough to keep it running, so I wasn't using the A/C. The compressor was definitely not turning on, though, and the short cycle didn't show up until I accidentally jumped the high pressure switch. So somehow that got the compressor working again, but I replaced the switches anyway to be safe.

Refelling the refrigerant then alleviated the short cycle issue.