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98 Taurus AC Overpressure Cycling

c130 on Thu March 22, 2012 1:48 PM User is offline

We just bought a 1998 Taurus LX from friends at church, for my son. It has the standard 3.0l ohv engine, automatic transmission, with the standard manual HVAC system.

The AC is only blowing hot air (around 100 degrees). While troubleshooting it I noticed the compressor was cycling on for approx 1 sec and then off for 15-30 seconds. Must be low on Freon, so I put some dye in the system and let it cycle for a while. Using the black light and yellow glasses I could not find a leak anywhere. Even waited over night and have not found any leaks. I decided to jump the low pressure cycling switch and it made no change. Compressor sounded like it was straining, so I hooked up my manifold gauge set up on it.

When the compressor clutch would kick in the high side pressure would rocket up to 450 psi +, and low side would drop to the 29 psi range. I was like ouch!! Well obviously the high pressure switch is working. So while scratching my head over this, I went to close my valves and accidently open wrong valve (High side manifold port valve). Well that will get your attention fast! But now after the loss of some Freon the system is now hitting 350psi on the high side and low side is dropping to 22 psi, and the compressor is kicking off. Well low side switch is working. So I put just a small amount of Freon back in and the pressure started to spike over 400 again. Checked both cooling fans are running just fine.

According to the data I have the High Pressure switch is supposed to open at 415-445 psi and then reclose at 220-280 psi and resume operation. This is what the readings on the gauge reflected. On the low side the switch is supposed to open at 23.5psi and then close at 45 psi, again this is what is being displayed on the gage after operating the wrong valve and dumped some of the Freon/gas.
After doing some reading I am convinced it is not the Freon servicing being high or low. What I have found online after reading for hours about this is that it very well could be a clogged orifice tube. So I figure my next step is to have the system evacuated, and replace the orifice tube.

Compressor also looks extremely new. I asked previous owner and he said he has no idea if it had been replaced. He said his wife took care of the cars problems on her own with a local dealership or repair shops. I cannot ask her as she passed this Christmas.

What are the technician’s opinions on this matter is my thinking reasonable/logical?

mk378 on Thu March 22, 2012 9:32 PM User is offline

You should evacuate, check the OT, and recharge by weight. Generally a blockage will not cause excessive high side pressure, instead the low side will drop immediately. Possibly it is contaminated with air and / or overchaged. This is assuming the condenser fans work fully like you said. Also there could be too much oil. Too much oil just crowds out the refrigerant.

c130 on Thu March 22, 2012 9:44 PM User is offline

Okay plan is have the system evac'd. Check orifice tube and its condition, change. Flush system if possible, and vacuum leak check. Re-service oil and 134a. Check condenser.


Edited: Thu March 22, 2012 at 9:51 PM by c130

mk378 on Thu March 22, 2012 10:44 PM User is offline

Also if the old compressor came apart inside and died, then someone just slapped a new one on, the condenser could be clogged up.

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