AC Issues

[honkon]

Ac only works when stopped, and compressor engages/cycles erratically.
When the ac is turned on sometimes it'll take 5 minutes for the compressor to even engage. Once it does, the pressures seem pretty good to me. 135 on the low side and 190-200 on the high side at 70-75F. It doesn't cycle like it should though. When I had the gauges hooked up to it it ran nonstop for about 10-15 minutes until I shut it off. I've noticed it cycling normally while stopped a few times, but I didn't have the gauges hooked up.
It doesn't really get cold, just decently cool, and as soon as you start moving it gets warm again.
Any ideas? Electrical? Compressor? Just low on refrigerant?

 

[df2x4]

Mine in my '97 Suburban is behaving similarly, has been for a year or so. I've had it checked out by my mechanic and it's not low on refrigerant or leaking from anywhere. Mine never has any delay kicking on, it just seems to run forever and not get as cold as it should. Also seems to be more effective when I'm moving, which sounds like the opposite of what you're experiencing. He found some gunk in my orifice tube, that's the only thing out of the ordinary. He's of the belief that my problem is my compressor slowly starting to kick the bucket. I believe him. It is 21 years old now.

Just out of curiosity does yours seem to get colder at the vents if you leave the blower on low? Mine does.

 

[shamrock246]

Even at 75 degs i would think the low side should be lower 135 and the high side should be higher 200

 

[shamrock246]

The specs in my book are @80F 28 low side and 320 high side. How old is the compressor? Has the orifice tubed failed?

 

[honkon]

The specs in my book are @80F 28 low side and 320 high side. How old is the compressor? Has the orifice tubed failed?

You're right. I mistyped my low side pressure. I meant 35 instead of 135. 38 to be exact, that's what I wrote down.
320 at 80F seems way high to me. Is your book specific to gmt400s? I was using this chart, and another resource that said the high side should be twice the ambient temp plus 50. According to that 200 is right on.

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The compressor looks like it could be original and is sort of noisy when it's running. Wouldn't surprise me at all if it's going out. The drier looks relatively new though, so I dunno. Compressor has an AC Delco sticker on it Not sure how I'm supposed to inspect the orifice tube without opening the system up.

 

[shamrock246]

I got the numbers from Haynes heating and air conditioning manual it's what they listed for a 1997 Chevy Tahoe,Suburban. If i remember correctly my high side was close to 300 but i replaced the compressor,orifice tube,dryer,any lines that were leaking.What is the discharge air temp in the vents?

 

[smdk2500]

It sounds like its low on refrigerant. The pt chart that was posted is what the pressures should be at certain ambient temps regardless of what type of vehicle the system is in. Going off the chart. If you have higher pressure then your suppose to your either overcharged or have a airflow problem across your condenser. If its lower the its suppose to you either are low on refrigerant an airflow problem across your evap and the refrigerant isn't boil away pulling away heat. If the low side is really high or or matches the high side your compressor is not turning or has damaged low side parts.

 

[honkon]

Mine in my '97 Suburban is behaving similarly, has been for a year or so. I've had it checked out by my mechanic and it's not low on refrigerant or leaking from anywhere. Mine never has any delay kicking on, it just seems to run forever and not get as cold as it should. Also seems to be more effective when I'm moving, which sounds like the opposite of what you're experiencing. He found some gunk in my orifice tube, that's the only thing out of the ordinary. He's of the belief that my problem is my compressor slowly starting to kick the bucket. I believe him. It is 21 years old now.

Just out of curiosity does yours seem to get colder at the vents if you leave the blower on low? Mine does.

I haven't noticed that. Our problems seem to be different. Mine rarely works anymore. Haven't been able to get a vent temp because of that.
I'm just gonna add some refrigerant and see if that helps. It's steadily gotten worse over time, as if it's caused by the refrigerant slowly leaking out.

 

[honkon]

A couple days ago I tried to add some refrigerant to the system. I had to jump the low side switch to cycle the compressor manually a couple times before it started doing it on its own.
I got it to take refrigerant and the pressures got up to where they were supposed to be and the compressor was cycling as it should. Vent temps were about 50 degrees. Then after 10 minutes or so of still sitting there hooked up to the manifold and can of refrigerant they fell back down to right about where they were when I started and the compressor was running pretty much continuously. The ***** with that? It wasn't obviously leaking out anywhere.
After that I unhooked it and drove it around for a bit and after about 10 minutes it was completely warm again. Compressor wasn't cycling anymore. I've driven it about 100 miles since and it hasn't worked at all.
Any ideas? How do I go about diagnosing the electrical components of the system? I assume the switches are supposed to have certain resistances or something. Where can I find that info?
I'm gonna hook the gauges back up tonight and see what the pressures look like.

 

[L31MaxExpress]

The cycling switch on the accumulator is bad about going out. I had several go on my Express van to the point I kept a spare in the glovebox. I swapped that switch and connector back to the older adjustable style and have not had an issue since. From GM the accumulator has a shrader valve in it where it threads on and refrigerant loss is minimal changing it out.