A/C 200q20v update

TooManyAudis at aol.com TooManyAudis at aol.com
Wed May 26 23:53:39 EDT 2004

After getting some advice from the list regarding my 200q20v A/C system that 
suffered alternately from low-pressure cutoff and high-pressure cutoff, I got 
out my guages and my manual to play a little game of Ask Mr. Bentley.

I pretty much figured that the low-pressure cutoff was due to slightly less 
R-134A in the system than should be.  It's amazing how, at times, just a few 
ounces can really improve the performance of an A/C system.

System was getting below 10 psi, and triggering the cutoff.  That was simple 
enough to address.

Then, came the high side.  I tested the high-pressure switch to the 
compressor, and it worked with no problem I figured this to be the case since it would 
periodically cut off.

Then, I tested the high-speed fan switch.  This, if you remember, was my 
original hypothesis.  I pulled the plug, jumped the wires and the fan kicked up a 
notch.  So, at least the wiring was good.

Time to test everything while running.  

Thanks to the additional 134A, the compressor stayed on.  Low side was about 
20 or so.  High side 300 to 350.  Fan hit second gear almost immediately.  I 
didn't know how high the high side should be, but this seemed pretty damn high 
to me.  Also made the high-pressure cutoffs quite understandable.

So, time to Ask Mr. Bentley.  After a few flow charts, verdict was 
"restriction in expansion orifice" or something like that.  Remember the orifice tube I 
chose not to replace when I converted the system?  I do.  Luckily, I didn't 
have to wait 5 days to get the part UPS'd to me.  Remembering that Autozone had 
my receiver/drier on hand, I thought it was a good chance that a FLAP would 
have the orifice tube, which it did.  There are some advantages to what is 
essentially a GM A/C system in our cars.

$2.98 later, I had my new orifice tube.  Back to the homestead where I let 
the 134A fly, removed the old orifice tube, installed the new one, vacuumed out 
the system and recharged.  I tell you, that vacuum pump is perhaps my best 
investment -- besides the $5 full size floor jack I got at a yard sale.

System now running at 25 to 30 on the low side, 200 to 240 on the high, with 
the fan jumping speeds right at the 200 psi mark.  The true test will be 
tomorrow -- 210 miles each way to Charlotte and back in 95-degree heat.  I am a 

The old orifice was just caked with crud.  I'm hoping that the crud is the 
result of the first 14 years of the car's life, and not just the last 6 months 
it has been with me.

In any case, learn from my mistakes, replace that orifice tube when you are 
servicing your A/C.

Charleston, SC

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