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


After a month of sweating it out, I now have air conditioning once  
again, but something appears to be wrong: the compressor runs  
constantly whenever the A/C is on.

Known quantities:

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.

Travis Graham

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