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Originally Posted by pitteach
Thanks busboy for the info. I've only had the truck about 1 month, so I don't know how the A/C was lost. I knew it was not working when I bought the truck. The truck spent all of its life in Florida so it is likely that the system is out of juice due to extended use. My question is will the lack of freon cause the clutch/compressor not to engage? I would think that if it didn't, then I'm definitely looking at a electrical malfunction?
Its not a big deal if I get this fixed or not seeing as how the truck now resides in sunny Buffalo, NY. But it would be nice to have if it is easy and reasonable enough to fix--otherwise the truck is in great shape.
You mentioned the clutch cycle switch, would that be what I am seeing on the schematic as the thermo-switch behind the dash?
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Hi
to the first question I would say yes. The system should not run if the freon level/pressure is not above a minimum. That pressure has to be measured by a sensor/switch of some kind. I did a bit of looking online at a parts house for '90 Nissan pickup and saw a Thermal switch, and a pressure cutoff switch. I would be surprised if the switch which cycles the a/c compressor clutch on your truck is located outside of the engine compartment, but I have zero experience with Nissan, or any other Japanese manufacturer. Ford switches sense actual freon system pressure on the low and high side. The low side switch cycles the compressor clutch on and off. If I had to guess at the Nissan part equivalent I would guess the thermal switch, as the pressure cutoff switch to me implies that it is a limiter, or a high pressure cutoff switch - but I am only guessing.
I would start at the compressor and go each direction - high and low pressure. The high side line should head from the compressor toward the condenser (small "radiator" usually mounted ahead of the actual radiator). The low or suction side should run from the compressor up to the firewall - of course the freon on that side is actually running the other direction being suctioned from the evaporator core inside the truck. As Wiswind suggested, I should think you will find a sensor/switch along each "side". One should limit the high side pressure, the other should sense the low. The one on the low side likely controls the comressor clutch - unless Nissan contols their systems completely differently. You may also be able to tell by which switch's wires are the same color as those at the a/c clutch - assuming Nissan matches them up.
Good luck to you. I have had the a/c blasting many times in BUF. It can be pretty warm and sticky over there.