I have concluded that I have ac leak but I can't find it. 1st question will the ac clutch engage if the coolent level is low? OK, here are my symtems. Last Summer everything worked fine. So it all started this spring. I turned on the AC and just about nothing happened. It cooled only a couple of degrees. I have a pressure checker; but I am not real sure what this thing tells you. I put it on, and the pressure was within normal range, and clutch engaged. So I went ahead and added coolent anyway. "a 14 oz can" That did the trick ac was blowing out cold air once again. The funny thing was that the pressure on the guage was in the exact some spot at about 25. A few weeks later it happened again this time I bought a leak detector kit. I put the uv in my ac system. I used the black light but I can't find any leaks. From what I see there is not much to the ac under the hood. I see the acumulator, condensor, and compressor, and the tubes that connect everything. So where is the leak? And one more thing why when cars are off I have noticed not only on mine but on otheres that the pressure rises greatly?

More than likely the leak is in the fins of either the condenser, or evaporator. Look for a dent in the fins of the condenser (behind the grille) where a stone might have hit the fins, and punched a small hole in the tube. Because of the direction of air flow through the condenser most of the leakage will probably be on the back side of the condenser between the condenser and radiator. Very hard to see. You can't see the evaporator as it is completely inside the A/C heater box on the firewall. Only way to find a leak in here is with an electronic style leak detector. Another spot to check is the front seal of the compressor. This is usually evident by a line of oil on the bottom of the hood where the clutch slings it.

Pressure on the output of the compressor usually runs around 250 to 300 PSI depending on the outside temperature. Pressure on the suction side usually runs around 20 to 25 psi and is controlled by the orifice tube or temperature control valve in the evaporator When you shut the car down the pressure equalizes throughout the system.

It is important to know what temperatures different points of the A/C system should be.

The discharge line (line from compressor to top of condenser) should be hot (heat of compression).

The condenser should cool the refrigerant from a high-pressure gas and condense it to a high-pressure liquid.

The liquid line (line from bottom of the condenser to drier if present) should be warm.

Second liquid line if present (line from the drier to the expansion valve located at the bottom of the evaporator) should be warm. If the drier is plugged this line will be cool.

The evaporator should be cold because of the refrigerant evaporating in it.

The suction line (line from the top of the evaporator to the compressor) should be cold. If the refrigerant is not flowing properly or if the suction pressure is not getting low enough, there will not be sufficient cooling.