I bought an AC Kit to check out the AC pressure on my 94 Volvo. Between the compressor engaging and disengaging I'm reading 25 to 45 psi. My questions are:

-What is the normal pressure reading when the system is engaged?

-Do I need to add coolant and how much?

Thanks,
Mark

You need to add refrigerant. Put in a pound or less and check it. Your low side pressure should be in the area of 30-35 pounds and fairly steady. The compressor keeps cutting in and out because it is low on refrigerant. When the compressor pulls the low side down to less than 30 or so it cuts out and when the pressure creeps back up to 45 or so it will rengage. If you have enough refrigerant in it that it cannot pull it down to less than 30 pounds then it will stay engaged like it should. If I am not evacuating the system I will usually meter in around 8 ozs. to 1lb. as I watch the pressures. If at one pound the pressures are stable and it blows cold I install some tracer dye in the system and ship it.