Sometimes, if it ain’t broke…

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
too much.

If you’re a service professional and not a MACS member yet, you should be! Become a member and receive a technical newsletter with information like what you’ve just read in this blog post visit for more information.

You can E-mail us at . To locate a Mobile Air Conditioning Society member repair shop in your area. Click here to find out more about your car’s mobile A/C and engine cooling system.

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.


About macsworldwide

Mobile Air Conditioning Society (MACS) Worldwide Founded in 1981, MACS is the leading non-profit trade association for the mobile air conditioning, heating and engine cooling system segment of the automotive aftermarket. Since 1991, MACS has assisted more than 600,000 technicians to comply with the 1990 U.S. EPA Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment. The Mobile Air Conditioning Society (MACS) Worldwide’s mission is clear and focused--as the recognized global authority on mobile air conditioning and heat transfer industry issues.
This entry was posted in Automotive, Automotive Aftermarket, Automotive training, Mobile Air Conditioning, Uncategorized and tagged , , , , , , , , . Bookmark the permalink.

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