QuestionDear Mr. Sudderth,
I would really appreciate your help solving my problem with A/C functioning. I recently purchased this used car, and A/C did not work. Previous owner mentioned that he attempted to recharge it with 134 gas but it did not help. When I turned the A/C on, relay clicked but compressor clutch was not engaging. I disconnected all harnesses and cleaned them with electronic contacts cleaner, them reattached. For a few seconds A/C started to work but then stalled. I gently tapped a low pressure switch and noticed that A/C comes on for a moment. Then I "discovered" a screw on the inside of the switch between contacts. I started turning it counterclockwise, then I attached connector back. Clutch engaged and A/C begun to work. Here is my QUESTION:
Does that screw "sits" there for a reason or it is simply holding something? I'm afraid to touch it again... Is that switch defective? If I replace it, should I discharge the system or it can be done without it?
Many thanks for your help!
Sincerely,
Leonard Manevich
ANSWER: Leonard,
The switch should be non adjustable and the screw should only be there to hold things together. The problem you have could be a couple of things. First, the easy one is that it is low on refrigerant. Second, the expansion valve could be hanging and that would over-pressurize the system causing the compressor to turn off. Have the system pressures checked to know for sure. The first fix is cheap with just a can or so of R-134. THe second involves pulling the evaporator core to repair.
---------- FOLLOW-UP ----------
QUESTION: Dear Mr. Sudderth,
Many thanks for your reply. I'm afraid that I got more confused and confusing you too. The last time I worked on replacing A/C system on 1977 Pontiac was about 15 years ago... So, please, be patient with me. After all, I'm professional journalist and musician but just amateur mechanic.
In my 1998 Nissan Quest I was talking about the switch that is located on the accumulator (round black canister). In the FSM it is named a "low pressure switch", but when I came to the parts store and asked to take a look at a new one, it was listed as "cycling switch". There IS a headless screw intended for adjustment. When I removed it from the switch (from the store switch), there was a small coil spring. When I adjust this srew in the car, it changes cycle time - compressor clutch either turnes on and off every few seconds if I screw it deeper, or every 30-50 seconds if I turn it counterclockwise...
Please tell me why this switch is called 2 names and how to adjust it for proper cylcing time (what is that time should be?) As far as I understand, compressor should not stay on all the time? Am I right?
Best Regards,
Leonard Manevich
AnswerLeonard,
After further research I find you have answered the question on the pressure cycling switch. It is adjustable. But, I have never adjusted one since they are set to cycle at specific pressures. Here is the other part of the switch. When refrigerant gets too low the pressure switch will turn off the compressor saving it from burning up. When the pressure is too high it will turn the system off to prevent the hoses from blowing. Now, what we need to do is to get the switch set back to the original setting and have the system checked using gauges to determine what the pressures are. Then, add until you are full or remove until you are at the proper pressure.
