Determining Amount of R12 in System

[89LSC]

My A/C doesn't work but I am not positive that there is a leak. The car is 12 years old. How can I determine if there is any R12 left in my system? My compressor is not engaging but I know the compressor won't engage if there is too low a level of R12.

[WILLIAM SHIREY]

Remove the connector on the Clutch cycling pressure switch and jumper the connector with a short length of wire. The pressure switch is screwed into the air dryer/accumulator. With the switch bypassed, the a/c compressor ahould run continuously. To really know how much freon is in the system, you need a gauge set. They usually run about $30 or so. I bought mine at WW Grainger. Good luck!

[This message has been edited by WILLIAM SHIREY (edited July 10, 2001).]

[Lscman]

You can use a tire gauge on the A/C schrader valve, if the air has been turned off for several hrs. Make sure it seats squarely so you don't lose much gas. For super safety, use leather gloves to prevent 100+ psi gas from penetrating skin under high pressure and kill you. This precaution is really only necessary if you're messing with the high pressure valves while the system is running. If the gauge value while off is under 70 psi, it needs charged. In non-technical terms, the system equalizes hi & lo pressure when off for a good while. When the compressor runs, the high side valve pressure goes up and the low side pressure goes down. This pressure differential is what creates the wonderful temperature differential between the condensor and evaporator coils (PV=nRT). When the low side pressure drops below 25 psi, a switch on the dehydrator opens the clutch circuit. There are other switches, but this is primarily how/why the system "cycles" when everything is normal. You can buy gauges almost any auto discount shop for about $40. Readings of 40 lbs (low side) and 170 lbs (high side) are typical but the chart in Helms is gospel. Pressures less than that indicate more gas needed. The high pressure will increase quickly when excess gas is installed and guage will exceed 200 psi. The gauges are worthless unless the compressor is running! A $3 tire guage will do the same thing with clutch off. Have fun finding R12, you may be forced to convert or have a shop do the work. Sorry, I only have about 25 lb of R12 left and I need it.

[This message has been edited by Lscman (edited July 11, 2001).]

[Charlie]

You can still find R12 at least locally. It is about 60 bucks a pound though and you have to hire someone with a license to put it in. Which of corse means they charge you a lot. My car had been converted when I bought it. I got it to work. It still doesn't cool as fast as R12 though. If you only need to add a little I personaly beleve you are better off to stay with R12. If you need work done it is just as well off to change and get it over with. I read something on the net about being able to get you own license and buy R12 for 40 a pound. I don't have that info here now if you are interested let me know and I'll see if I can find it. I too horded some of the stuff when you could still get it, and sorry but no, I have none for sale.

[Richard J. Parker]

Some other "rules of thumb" on A/C System Diagnosis
http://bridges.eiccd.cc.ia.us/~dhanan/hac/LESSON8.TRN.doc


Complete "course" on AC...
http://bridges.eiccd.cc.ia.us/~dhanan/hac/AT134.html


[This message has been edited by Richard J. Parker (edited July 11, 2001).]

[LSC4ME]

The most common problem are the o-rings.the original ones were prone to failure.Ford now sells upgraded,improved ones.I believe they are green.

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1991 Lincoln LSC Special Edition(Black Beauty)
1990 Cougar LS 3.8 (Damn head gaskets!!)
1988 Chevy K1500 Ext Cab Longbed
"IF IT AIN'T RWD I AIN'T DRIVIN'IT"

[WILLIAM SHIREY]

LSCMAN:
Are the pressure numbers you stated for engine at fast idle(A/C running) or a higher RPM, i.e. racing the engine? Thanks.

[Lscman]

The pressure differential occurs when the engine is running. Just about any manual will tell you what A/C hi and lo side pressures you should be reading and what RPM. It depend upon the vehicle, the relative humidity and the air temperature. The ball park one's I mentioned are for "high idle" speed testing, around 1500 RPM. I try to install freon when the humidity is low and the air is between 70 and 80 degrees F. Adding more R12 to the system will increase the pressures and interior "cooling effect" until you exceed a certain value and the compressor begins pumping fluid. At that point, the high side pressures go too high and the compressor will fail. I would not suggest using my simplified instructions without reading the manual.