I drove the car for the first time this year and the a/c seems low on charge. The compressor is short cycling.

When I removed both the high side and low side caps I heard a short hissing noise. I wasn't sure it this really signifies a small leak or if it's normal?

I checked the lines and condenser as best I could with a black light as there is already dye in the system and didn't see anything. It was fine when I put it away last year.

I also have a halogen leak detector and couldn't find anything.

Any ideas would be greatly appreciated.

 

Those valves are not supposed to leak. They can be and should be replaced if leaking. If you could hear gas leaking out of the valve, why didn't the leak detector show it was leaking? I replaced them when I did my '96.

 

Thanks for the info.

I ordered the valves. The leak detector does seem to sense a possible leak from the high side but gives an inconsistent beeping. Since the system is pretty low on freon I'm going to change both ports and hope that resolves it.

 

It's not unusual to have a small amount of freon leak past the charging port valves and escape when you remove the caps, but it should be very minimal. The caps also have seals in them and I would recommend replacing them outright because I don't think you can buy the seals separately.

However, if you haven't gone through the entire system, with it being 25 years old I'd strongly recommend doing that. At the very least buy an o-ring kit, caps and those valve cores and be sure to clean out (or replace) the orifice tube where it goes into the evaporator core.

Other places to check for leaks are the evap and condenser cores. Unfortunately if the condenser core's leaking and can't be repaired the only options I found were salvaged parts.

Last fall I performed a complete system cleaning and re-seal of the compressor on my '95. The sucky parts were getting the condenser and evap cores out to flush all the old PAG out. It was an entire weekend project, but well worth the time. The compressor wasn't terribly difficult to re-seal - the only tricky part was installing the shaft seal with the tool that was included in the kit. All in I think I spent less than $250 including a new receiver / dryer, PAG and 134a. Now I know the system has the correct oil and freon charge, and on a hot day it will freeze you out until the climate control hits 60F inside and starts reducing compressor duty cycle.

 

I got lucky on my '96. I simply replaced the stems in the shrader valves, used my yellow jacket pump to draw down and refill. It has been ice cold again now for the last 3 or 4 years. I bought the pump, gauges and accessories for about the sum the dealership would have charged me for a refill. I did another vehicle also so I am well ahead of the game and have all equipment to do vehicles in the future. These quicky refill aerosol bottles at the parts store might be okay if miles away on a trip to get you home but doing it all the right way is the only way to fly.