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Compressor Cycling Problem

cat7195 on Sun July 10, 2011 10:02 PM User is offlineView users profile

Year: 1993
Make: Ford Truck
Model: F-150
Engine Size: 5.0
Refrigerant Type: R-12
Ambient Temp: 90 F
Pressure Low: 26 F
Pressure High: 204 PSI
Country of Origin: United States

My F-150 is a 130,00 mile occasional use work truck I've owned for about 5 years. The a/c system does not appear to have ever been worked on. The a/c worked fine until recently. The problem started this spring, when driving up a slight incline on the freeway you could feel the compressor kick off and warm air start coming from the vents. When the freeway leveled out the a/c would come back on.

Now when you start the truck and turn on the air, it blows cold for about 30 seconds to one minute and then the compressor kicks off. The compressor then cycles on and off about every 30 seconds but it doesn't blows cold again. Shut the engine off, wait 10 or 15 minutes, start the engine and it goes through the same routine.

A friend helped me take the readings today. After he left, I decided to try jumping the pressure cycling switch. When I took the 2 wire connector off the switch, I found one of the connector terminals corroded. I cut the connector off and crimped on 2 individual terminals. I connected them with a jumper wire and started the truck. It blew cold for the 30 seconds to one minute. After the initial cold air, the compressor kept running but it started blowing warm air.

Any ideas what is causing this and what needs to be done to fix it?

I don't know if any of the a/c functions go through the EEC, but I replaced the EEC for a fuel pump problem a couple months before the a/c problem started.

JJM on Mon July 11, 2011 8:15 PM User is offline

What are the high and low pressure readings when the compressor is continuously engaged and blowing warm air? Are the suction lines icing up?

If the high and low pressure readings are almost same and the suction lines are warm, the FS-10 is likely done. The short cycling was probably the result of refrigerant loss, and along with refrigerant loss there was oil loss, and along with low refrigerant and low oil, the FS-10 gave up the ghost.

Condition of the OT will tell much...


When considering your next auto A/C purchase, please consider the site that supports you:

cat7195 on Mon July 11, 2011 10:39 PM User is offlineView users profile

The suction line was not icing up.

I'll get the pressure readings Wednesday morning and post them.



cat7195 on Thu July 14, 2011 7:48 PM User is offlineView users profile

I ended up taking the truck to an automotive air conditioning shop. Their diagnosis is the compressor is starting to fail. As JJM posted, it's a result of refrigerant loss and oil loss causing the compressor to fail. To repair the system they recommend flushing the system, a new Motorcraft compressor and clutch, a new fan clutch, a new accumulator, and a new orfice tube.

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