Poor Air Conditioning

I have a 1996 Jaguar XJ6 VP, with 99,000 miles, that stands unused for months at a time. Last summer I had no air conditioning at all. I added two 14 oz cans of EZ Chill, and got satisfactory cooling, though not as good as I remembered. This summer I added another can. In doing so the can got very cold and the area around the low pressure port I was using showed signs of frosting. The gauge briefly went into the green area but imedially dropped back to zero. The engine was running and air conditioning control set to full on and fan on high. This all was to no avail in fact there is less air conditioning, and sometimes non. With the engine off the system press is 75 – 92 psi depending on ambient temperature. When the engine is running and air condition control full on the low port pressure is zero.
Has anyone any ideas what is going on?

You have a leak. The leak may be bad enough now that the system cannot maintaon adequate pressures. A good A/C technician can find this leak pretty quickly.

Thanks. I thought I had a leak due to none use and drying seals, but it seem to retain some charge through last winter because this summer it had some A/C. and with engine off retains 75 - 90 psi.as long as I have been monitoring - for several days now.

The static pressure of 75-92 PSI is way too low and means undercharged or loss due to a leak.
It should be up in the 120 PSI range.

The low side intermittently showing a zero reading could be due to an expansion valve acting up and sticking almost, if not all the way, closed. It would be interesting to know if the high side pressure rose when this happens.

Is the compressor cycling off and on fairly quickly? If so, you’re likely either low on charge, or have overcharged the system. With the gauge dropping to 0, assuming it’s not just a lousy gauge like some of the do-it-yourself kits have, I’d suspect undercharged or something wrong with the system. Obviously you have at least a slow leak or you wouldn’t have had to add refrigerant. The refrigerant could also be contaminated if anything but the correct refrigerant (probably R134a) was used.

I’d probably shell out the money and have it professionally evacuated and recharged if you care about the car at all, before you make matters worse.