My a/c compressor crapped out a summer or two ago. I ordered a new compressor and dryer, oiled up the compressor properly, hooked it all up, vacuumed out the system, filled it with fresh 134a and it worked just fine for about a year. Mid-late last summer, the a/c quit working, so I hooked up my gauges to check it out.

Everything reads in the proper range. The high side is only about 150, which isn't stellar, but not terrible either - certainly enough to cool things down. Anyways, when I was sitting at idle checking things out, my compressor was running all the time and not cycling on or off. Given that I was not overcharged (according to my HF gauges), I tried to add a little more to it. It would only take half a bottle and the compressor never started cycling on/off, so I stopped tinkering with it for a while to think on it. I noticed that when I had it on driving in town, I could hear the a/c kick on and off every couple seconds like it was still low, but my gauges didn't indicate that it was low and it wasn't taking a charge like it was low. This whole time, the air from the vents is not even cool - just straight outside air temp and the lines don't feel cold either.

I had hot-wired my compressor to stay on and same story. The gauges show it's compressing with the low side right where it's supposed to be and the high side a tad low at idle, but easily jumping up to within spec with mild revs. The whole time, the vents and a/c lines are no colder than ambient.

 

Alot depends on the outside temps....If you have 80 degs then the high should be way higher like up to 300...for 90 deg. 150 psi for about 70 deg as far as I remember.

Also the inside controls may be screwed up. check the doors for proper orientation...Check for cold return line coming back to the compressor.

Oh lines aren't cold just read that...something is clogged or broke...looks like its gotta come apart.. Check orifice tube.

 

Give us the actual readings, because the information you have about the reading being right where they're supposed to be doesn't tell us anything if you have the wrong information.

 

On my ~80 degree day, low side was about 45 and high ~150 at idle. Closer to 38/220 at mild/moderate revs.

I'd thought about plugged orfice tube, dryer, evaporator, etc, but then the high side would read something silly high as instead of a bit low.

I'm almost starting to wonder if my gauges are junk because I can't make any sense of this. I guess that wouldn't surprise me given that they're HF gauges. My first set of HF gauges literally didn't even last me 5 minutes until they blew out an internal o-ring.

 

Your readings should be more like 30 and 225. To me it seems the compressor isn't running long enough to build pressure. Since your compressor is cycling on and off and it seems like it has sufficient charge, I'd look into the low pressure switch being inaccurate.

 

agreed 30 & 200plus at high idle would be great.

plus the suction line coming out of the evap should be freezing and maybe even all frosted up depending on humidty
if you can get good numbers and the suction line is cold then pinch off the heater hoses in case its some kinda blend door issue

 

That is a good thought on the low pressure switch, but I had jimmy-rigged the compressor to run all the time and have the same issue, so that's probably not the culprit. It has to be something in the system - just not sure what as my readings looked at least reasonable.

I may have to break out my gauge set and revisit this after taking a break over winter. Perhaps I'm remembering incorrectly or something because this is making absolutely zero sense to me.

 

Sounds like your cooling fan control module (magnet/fan clutch) may be taking a dump. If the register air is great while driving I would look into the cooling fan system.
Basically, the engine fan is not pulling enough air across the condenser. If you have an IR thermometer, compare the in and out temps at the condenser. The readings should not be the same, maybe a 30-40 degree difference.

 

Well, it's not that either. The fan is pulling air just great and there are no blockages in the grill. Even on the highway, the air is ambient.

I'm gonna have to break out my gauges again and see if I was getting some goofy reading or something for whatever reason.

 

check the high side line it should be hot.

 

Check it CAUTIOUSLY. It can get very hot, hot enough to give you a bit of a burn if you're not careful.

While you're at it, check the inlet and outlet lines at the firewall.