: AC Problems Fixed!

05-30-06, 12:08 AM
Not sure if this is the best place for this but I figured I would pass the
info along. Sorry this is long, but I hope to help someone else if they are
seeing issues like mine had. So feel free to move this around to a better forum, it really covers all cars. (Delete this section when you do moderators!) You might want to sticky this for the summer....

First and foremost. Get high/low side gauges. Do not use low side only,
they are useless alone. And easy to overpressurize and damage your system. If you aren't cozy comfy working on AC systems, don't, find a pro.

But they are very simple systems, lets do some confidence boosting here....
Compress freon, it gives off its heat, pass it through a heat exchanger, (condenser, as we make the freon gas a liquid again) then in order to make pressure, you need a restriction, being this is the smallest point in the system, GM put a filter there too, this is the point where the pressure goes from high to low, and the freon gets COLD and we send this directly to another heat exchanger inside the car, we call this the evaporator (where the liquid freon is fully expanded into a gas again) and goes into the accumulator where we ensure that there is no liquid freon to get into the compressor (lest it hydrolock and break), which it has a desiccant bag in to help reduce any moisture (if you open your system often and don't get it vacuumed down, you may need to replace more often than a well sealed system) Then we head to the compressor still as a gas, and then compress back to a liquid and we start all over. It really is this simple!!!

Note: My system has had 2 compressors replaced before I got the car, both in less than a year. Being a "professional", it should have been done
right. Maybe, maybe not. Read on....

My AC hasn't been working worth a darn this year. it worked ok last year,
but not fabulous. Figuring it was low freon (dumb assumption! Use your
low and high side gauges!!!) I added freon based on low side gauge only.
Too much freon now, it started to do weird things with the compressor.
When it would kick on, it would vibrate violently or it would spit out freon
violently. Almost like an overpressure valve was there (is there?) So I
bled some back off and it was ok, but not a bit of cold air. But the
compressor kept cycling a lot, 2-5 seconds only, very annoying. When I
finally put my gauges on, the low side pressure was dropping like a rock to
0, when it got low, the low pressure cutout turned off the compressor, and
the high side, was skyrocketing to 500+ psi (I suspect there is a high
pressure cutout too at 3.4bar). Thinking there was a blockage in the
system, I pulled the orifice and it did have some metal shavings in it
(yeah, that is creepy!), but they were caught in the filter. It wasn't by
any means plugged up. I cleaned it and reinstalled, and filled with 24 oz
freon (yeah, getting $$$$). (what I had on hand) No cold air at all. But,
by definition, I was low on freon, the low refrigerant check is the start
and run AC on max, and feel the AC line AFTER the orifice and the
accumulator. If they are both VERY cold and close to same temp, you are ok, but in my case the line after the orifice was cold, but the line out of the evaporator (the inside car heat exchanger) and the accumulator were warm. I had put in 24 oz, and (it calls for 28) and I wasn't sure why it wasn't giving me ANY cold air. So I added a little more, and things got worse again.

A friend of mine and I talked and figured there HAD to be another
restriction. Something plugging up after the compressor somewhere (the hot to cold temp changed was at the orifice still)

So I decided to take my friends advice and flush the lines with Acetone. I
disconnected the line going out of the back of the accumulator (the one
pointing at the firewall), remove the orifice, and then disconnect the line
between the condenser and the compressor. I then used a funnel and poured in nearly 1.5 qts of acetone till it started pouring out the (upper) line of the condenser. I let it sit for 20 min or so, then forced it out with 10-30 psi compressed air (watch it, be gentle on that with liquid in the lines, it can splash in your face if you aren't careful! I did that as a kid, it sucks!!!)

Once the lines were clear of the majority of the liquid, I went up to 100
psi air till the compressor died down (small one) and kept feeling the line
output and once it was dry, I then rigged up an old R134a fill kit (those
cheapie plastic ones) to engine vacuum via the one way check valve from the Opti vent line. I pulled it down to 19-20 inches and held it for 10 min or
so, then connected up my hand vacuum pump to get it to 25 inches. The
longer you pull it down, the more moisture you get out of the system. As
the pressure drops, the point at which the water, acetone, oil, etc boils is
higher, so it will evacuate the system much better. As when water is under
a vacuum, it will boil at room temp, and then be purged. If you don't get
the water out, the it takes up a tremendous amount of space in the system,
so it must be removed.

So once done, I added 2 oz oil and 28 oz freon, and the system is colder
than I have ever seen it. No more compressor cycling, and pressures were
back down to around 200-220 (Book pressures today's weather (at 2000 rpm) are around 260 to 345 psi, so I am low still, but have the right amount of freon in, so I am leaving it).

Remember, pressures are measured at 2000 rpm, doors and windows open, hood open, and if you don't have RPO V08, then add a high capacity fan in front of the condenser. Get the correct pressures for your car from a GM book, not some generic book like Hanes or Chiltons. Get GM book info.

05-30-06, 12:58 PM
Good for you!
I vacuumed mine down this weekend, and recharged it. I gauges read High on the low side , and low on the high side. I read on the net, that it is a problem with the compressor. Do you know it compressors are rebuildable? (at home)

05-30-06, 02:02 PM
Yes, but rarely people do. Get the FSM or get someone to copy it for you and tear it down. I don't know how much can be rebuilt, or if you can get parts, but it can be done....

06-02-06, 06:20 PM
Good for you!
I vacuumed mine down this weekend, and recharged it. I gauges read High on the low side , and low on the high side. I read on the net, that it is a problem with the compressor. Do you know it compressors are rebuildable? (at home)
The only part that is rebuildable by the average joe is the seal replacement. Of course, you need special tools which sometimes can be borrowed from your local AutoZone-type place. The actual seals are only a few bucks and can be bought on-line. A leaky seal is the most common problem with losing refrigerant. You can't rebuild a failed compressor (with failed compressor blades).