It’s easy for technicians to be misled by temperature and pressure readings, and what they think should be happening as a result of what they see. A high-mileage thirteen-year-old Mazda 626 isn’t cooling on an 85-degree day in New England. The technician finds that the low-pressure switch isn’t working, replaces it, and although the center register air temperature drops to 40 degrees, the clutch doesn’t cycle and the A/C pressures are 150 and 40 psi at idle. The technician decided that since it was a cycling clutch system, it had to cycle sometime, but he kept watching, and it wouldn’t.
The high-side pressure looked low and the low side looked high, possibly indicating a weak compressor or expansion valve stuck partly open. He also was ready to decide to look for a defective evaporator fin sensor, but the cooling performance was good and
the system wasn’t icing up, so a defective fin sensor wouldn’t make sense. Finally, he got the word that in high humidity (not the usual condition in the area), the system may not cycle, certainly not if the compressor can’t pull the suction side well below 40 psi. Might the compressor be a bit weak, might the pressure gauge readings be off, might the thermometer reading be optimistically low? Sure, but if the air is cold – and cool
air on the driver’s face is pretty obvious, don’t think
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Mobile A/C professionals should plan to attend 35th annual Mobile Air Conditioning Society (MACS) Worldwide Training Conference and Trade Show, Meet me at MACS Make Connections that Matter, February 5-7, 2015 at the Caribe Royale, Orlando, FL.