Re: [DML] A/C problem: compressor is not cycling
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Re: [DML] A/C problem: compressor is not cycling

Hi Travis

Here's what I can tell you about your system by looking at your data:
1. The spot where you have a leak will be covered in grease. It does not 
have to be a one single place, like an o-ring. It could be that the high 
press. hose is letting the refrigerant out. Check to see if the hose is 
greasy. If not, check the seal on the compressor shaft, o-rings at the back 
of the compressor, o-rings at the condenser (in front of the radiator). 
Remember that with a refrigerant leak you also loose the lubricant and you 
end up with a dry system. Don't forget to add oil to the system.

2. The temperatures are too high. 60 degrees is not cold at all. I was 
getting 40 to 45 degrees on my R134a converted D and the same with R-12 in 
my second car. That was in hot and humid Florida weather - around 90 
degrees. At that ambient temp the compressor might not cycle at idle.

3. Rest pressure is good. However your high pressure is low and low pressure 
is high. According to the shop manual for ambient temp of 90 your pressures 
at the compressor cut out point should be 170-200 and 25-32. If the low 
pressure is outside those limits then you will have to adjust the low 
pressure switch located on the accumulator/dryer. If the high pressure is 
too low then you either have a plugged inlet screen at the compressor, not 
enough oil in the system, or the compressor is just weak.

Looking at what you have done to the system and parts that you have replaced 
I would say that the compressor is weak and you will need to either replace 
it or have it rebuilt.
Remember that oil is a very important component in a well functioning A/C 
and is often forgotten. Every time there is a leak you loose the refrigerant 
and the oil with it.

I hope this helps

Good luck

Tom Niemczewski
vin 6149 (in Poland!)
Google earth: 52°25'17.30"N 21° 1'58.00"E

----- Original Message ----- 
> 1) The system has a small leak somewhere - it loses enough
> refrigerant to stop working after approximately 3 months.  I'm
> working on finding the leak, which is why I'm charging it up.
> 2) I charged the system yesterday and noticed that the compressor ran
> constantly.  Thinking that somehow I overcharged it, today I recycled
> the refrigerant, evacuated the system to 29 in-Hg for 30 minutes,
> held that for another 30 minutes (did not lose a bit of vacuum), then
> charged the system with 2.0 pounds of R-12 (purposefully
> undercharging it initially to see if it would cycle more
> frequently).  The air at the center vent is cold (40 deg. F when
> moving, around 60 when sitting), but the compressor still does not
> cycle (at least, as far as I can tell; I do have Fanzilla, so it's
> tough to tell if it's cycling when I'm moving).
> 3) The ambient temp. is a humid 90 degrees F and my cooling fans are
> running constantly with the A/C on.  Pressures from the manifold
> gauges are...
> rest pressure: 69 psi (low and high)
> @ idle:
> low side: 42 psi
> high side: 155 psi
> @ 2500 RPM (car not moving):
> low side: 28 psi
> high side: 206 psi
> 4) My orifice tube, accumulator, high and low pressure switches were
> replaced 4 months ago when the system was last recharged (and I'll
> replace the accumulator and orifice tube again when I open it up to
> replace whatever is leaking).  As far as I know, everything was
> working and the compressor was cycling normally the last time around,
> therefore, I don't suspect faulty switches (I didn't have gauges
> then, so I don't know the pressures).
> Section N:09 of the good book seems to point to a faulty orifice
> tube, clogged compressor inlet screen, or overcharging.  Given my
> data, could that be right?  I tested the calibration of the tank
> scale this morning, so I don't think I'm overcharged (especially
> since I only put 2.0 pounds in).
> Any advice on how to proceed would be greatly appreciated.
> Thanks!
> Travis Graham
> #6344
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