Psyco A/C

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Last week, we set out for a short business trip in the heat, and not long after hitting the road, it became clear that the over-the-road (OTR) air conditioning wasn’t doing its job. Since it was a short trip, just about a hundred miles, I told Jan I’d look into it once we got home. Fast forward to Friday evening—we’re heading back, and it’s still just as hot, so I turn the OTR air on again, hoping for at least a bit of relief. After about five miles, I start thinking, “Hey, it’s actually getting cooler in here.” Then Jan chimes in with, “Can you turn the fan down?” The OTR air was suddenly running perfectly. I had already checked the controls multiple times during the trip up and even tried turning the system off and back on. Any ideas on what’s happening here?

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I’m thinking the Carrier compressor might have an electric clutch that’s acting intermittently. If the issue pops up again, you could open the engine doors and check if it’s rotating. Personally, I always like to switch the AC on at the lowest RPM, figuring it’s easier on both the compressor and the clutch that way.

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Jack’s spot on about the clutch. There’s also a box in the first bay on the driver’s side that, along with the big circuit breaker for the system, houses some 8-pin base relays. If those relays have dirty points, that could explain the intermittent issues too. Unfortunately, troubleshooting when the system is working is often a dead end.

There are a lot of possible failure points, so it’s worth inspecting for any potential problems. The evaporator and condenser motors both have carbon brushes that need to be replaced when worn down. I wrote an article on the POG site about replacing these brushes when they hit their minimum length. An intermittent issue with either motor could throw the system off, though a failed condenser motor usually triggers the AC light.

Have you checked the freon flow through the sight glass in the receiver tank? I doubt that’s the issue since the system won’t magically refill between uses, but it’s something to keep an eye on.

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Thanks, Jack and Jon. If the OTR air acts up again, I’ll start by checking the clutch.

Jon, your comment about the system not refilling itself reminded me of a funny story. Back in the ’50s, my father had an engineer working for him who bought a brand-new VW Bug. The guy was raving about the incredible mileage he was getting. My dad and another colleague decided to have a little fun. They got a spare key to the guy’s car and began secretly adding a quart of gas to his tank every day. The engineer couldn’t stop bragging about his VW’s efficiency. After a few days, they bumped it up to half a gallon, and his boasting went through the roof.

Then, after a couple of weeks of this, they switched tactics and began siphoning gas out. First, just a quart, then gradually more until they were taking out over a gallon a day. His bragging came to an abrupt halt, and the other engineers would tease him about his mileage. But he just couldn’t bring himself to admit that his VW was getting only about 10 miles per gallon. They kept at it for months until one day, he caught them in the act. My dad said he’d never been called so many names in such a short span, but the guy eventually got over it, and they laughed about the prank for years.

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That is downright evil.

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Hi Ted. I thought my OTR was acting up on several occasions as well but I could never find anything wrong. It would cycle off. I believe it was the temperature guage.

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