My sons 1987 F150 AC compressor cycles continously, (with the AC on of course) , We did have to add freon when we bought the truck a few weeks ago to get it to cool properly, But is it normal for it to cycle off and on every few seconds? Thought with the age of truck this could be normal, any ideas or answers? Thanks

 

have you checked the compressor's clutch? it may be on all of the time.. just a tought.

 

Does it look like its slipping, or is it simply turning on then off? does the compressor have oil seeping out from around the clutch? Check the voltage at the clutch connector if its fluctuating or steady, if its steady may be time for a new compressor.

And just wondering if the proper refrigerant was used and amount which is 3.25 lbs

 

You most likely need more freon, the clutch should stay on continuously, the system might have a slight leak and you might want to get some stop leak with dye so if there is a leak you can see where it is.

 

if the system is continuously cycling it is almost always because the system is low on Freon. but if you have added twice already you have a leak somewhere, i would refill and ad dye into it, so you can see it. I wouldn't put stop leak in if iyou can help it. nasty nasty stuff. and it never comes out.

 

Can look for oily areas on system. Use thick liquid soap on connection and around shaft seal on compressor. Look for bubbles. Check drain on evaporator blower box for signs of oil. Oil travels with refrigerant in systems. Fire up ac. Run awhile turn off engine and listen. If the leak in bad enough you may hear it. Run a/c a while and turn off before checking with soap. Also a leak can be bad enough to blow off or thru the soap.

 

Also might be the low pressure switch. You need to put some guages on it and see what the pressures actually are. If the pressures look good then your switch might be bad.

 

If the weather is still cool, it may cycle as part of normal operation.

Essentially the condenser is able to remove heat from the system faster than the evaporator can add it back in, resulting in low-side pressures dropping below the cut-out level.

Typically noticed when the outdoor temperatures are, say, 70 degreesF and below and the engine is being operated well above idle speed. The clutch cycling time will lengthen as the outdoor temperatures warm up to a point where the clutch stays engaged all the time.

Not to say you don't have a problem - but if the vent air is cold and the freon pressures look good - it may just be one of those normal things.