Quote:
Originally Posted by 406 Q-ship
Vintage Air's binary switch (or trinary) is placed in the dryer (high pressure liquid cold side) of their systems and isn't necessarily a cycling switch but a system protection switch. Most of the OEM A/C system of which I am familiar, use a low pressure side switch to control the system pressure.
For me currently I am trying to convert my 74 C10 to a different form of clutch control. I converted to R134a years ago and the system worked but after letting the truck sit while redoing the engine the refrigerant leaked out. I refilled the system again but was having issues with the main inline fuse that kept turning the blower motor off and I believe freezing up the evaporator, at that the capillary cycle switch would shut the compressor down. So I am trying to use a low pressure switch from a later truck or GM car to control the compressor but I am concerned that the R12 might not have the adjustment range needed.
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Good info. Have you tried a LCO switch from a 93 or newer OBS? I think they were R134A I believe. Just to give you a little background on the system I'm working on. I have a 93 Silverado that I have installed a 2017 L86/8spd LT swap. I used 2017 PWM fans that are controlled by the computer. I replaced all the factory components with OEM stuff (pretty much the same system in a squadrebody) except for the compressor, which is a Sanden SD7. I used the factory AC low cut off switch and installed a 3 wire switch from the LT engine to control the fans. My only mistake was installing that switch in between the condenser and the dryer. I didn't think about the orifice tube being in the outlet of the condenser and therefore my switch wasn't seeing high enough pressures to kick the fans on. This was causing exceedingly high pressures that would not go down until the engine temp kick the fans on. I purchased a fitting that bolts onto the compressor discharge port and moved my fan pressure switch there. Now everything works as it should (fans come on almost immediately) and pressures are perfect. My only other concern is there is no high pressure protection other than the fan speed increasing (pressure based) and the SD7's pressure relief valve. Due the way the PWM fans are controlled, I'm not sure how to wire in a High Cutout switch without causing short cycling of the compressor. Maybe it's not necessary???