I have an E450 with V10 gas. AC is not functioning. The compressor clutch is short cycling, (on for about a second then off) a few seconds later is on again and then back off. I have 65 psi on the low side. The AC has never been worked on, never needed to be filled, etc. No one has added charge. The vehicle has sat for a couple years. It was started and ran once a month but AC was not used during that time. Could a failing AC relay give these symptoms or is something else wrong?

 

When the compressor is not run for either A/C or defrosters, the seals in the compressor and sometimes the"O" rings shrink and leak refrigerant..

The symptoms you describe most times are the result of a low refrigerant charge.

Technically,,,,,,,,,,,,,,,,,,,,,,,we are supposed to repair any leaks to preserve the environment
What you might consider,,,,,,,,,,,,,,,,,,obtain a can or two of R134A refrigerant and a kit to add that refrigerant to your vehicle's system. Most auto supply stores sell both including the place with the big yellow asterisk, where most folks shop. You can do it yourself.
If you decide to add the refrigerant you must wear safety glasses and follow the directions After you connect the can and hose to the LOW SIDE (Can't make a mistake, fittings won't let you !) start the engine, turn the A/C on high cold ,windows open and open the top of the can to allow the compressor to pull in the refrigerant. You should notice the on period of the compressor clutch get longer and eventually stay on. Even when fully charged it will open the clutch circuit to prevent freezing up the system..
When you feel the large aluminum can of the system, it gets cold and that is the time to stop adding refrigerant.MORE IS NOT BETTER !
If the leak is small you should be good for the summer.One word of CAUTION,,,,,,,,,,,when adding refrigerant, NEVER allow the can to tip over. That will
allow liquid refrigerant to get into the compressor and destroy it.
It is made to compress vapor ONLY.
You stated a pressure, does that mean you have a set of manifold gauges to use ? If so get back to me and will suggest what readings you should get and when !

 

I have gauges. I am perplexed at the moment.

Yesterday I had 65 psi on the low side. I swapped the AC relay with an incorrect 5 pin relay. I swapped back to the original relay and it continued to cycle. The cycles were too short so it was not functioning correctly.

Today I put gauges on it and it was at 35psi on the low side and the compressor is not cycling at all.

 

With the engine running, A/C selected,setting on high cold,low side reading in the area of 30 psi is considered normal and could be cycling around 6 times per minute.

At approx what engine RPM are the low and high side readings ?

 

the 35 pressure reading was taken at 0RPM and at idle. Right now the compressor is not cycling.

 

Do your manifold gauges show the pressure and temperature relationship ? At ambient temp of around 70 degrees F , static pressure should be around 80 psi..

 

The manifold is at 33.5 psi and ambient was around 58F. 80psi sounds very for static pressure. Are you sure about that?

 

Static pressure is the pressure you see on the gauge when you first hook it up and nothing as been turned on.
Manifold gauges usually show the pressure at that temp.

When the system is operating correctly, low side pressures are low and high side pressures are high.
Most leaks take place when pressures are at the higher end.

 

Ok, with the truck running I am at 33.5psi and compressor is not turning.

 

What is your high side reading at that time?