I have a trinary switch installed on my '40 Buick A/C system to switch on the electric fans when ever the A/C is turned on. It also has a thermostat in the radiator which will turn on the fans at 200 degrees F and a manual fan switch so I can turn them on as needed. If I remember, the trinary switch on the A/C system is designed to make the fans come on when the head pressure comes up on the unit. I noticed today that my fans would not come on, even after running the A/C for some time, unless the temp got to 200 degrees (which would make the fans come on from the thermostat in the radiator, no the trinary switch). My A/C unit seemed not to be cooling quite as well as usual, and I am wondering if these may be signs of low freon in my system. Would low freon in the system make the head pressure stay low and not turn on the fans thru the trinary switch? Any A/C folks out there that understand my system as described that may be able to shed a little light? thanks.....PACO

The trinary switch senses head pressure and when it typically gets to 270psi (+ or- 15lbs) it will turn on your fans. If you have been running the car on the road at any speed at all, the forced air will cool off your condenser and keep the head pressure down. If you are idling at a dead stop for any length of time, your headpressure will come up and your fans should come on. Your A/C will work much better if you manually turn on your fans when you are in heavy traffic rather than wait for the trinary to turn them on. If you suspect that you are low on refrigerant, check your reciever-drier for a sight glass. If it has one, look for bubbles. A r134a system should have just a few bubbles now and then. A r12 system should be clear. A good indicator of leaks is a slight oil film near fittings or near the front of the compressor. Your a/c system has oil suspended in the refrigerant and if there is a leak, it will generally leave a film of oil in that area.