It's always a challenge to diagnose and repair those weird driveability problems, but any full-time tech will tell you that
the more routine jobs are the ones that fill your day: brake work, minor maintenance items and, of course, A/C repairs. In
my part of the country, keeping customers' A/C systems up and running is a year-round request.
A simple A/C repair
This past winter was the warmest on record for us, so this Mountaineer customer had been making full use of his dual A/C system.
He was complaining, however, that the rear unit was blowing warm and that there was an unfamiliar noise under the hood when
the A/C was turned on. I grabbed the keys from my service advisor and brought it in to check it out.
When I have an A/C-related complaint, before even pulling into the shop I like to start the vehicle to check the operation
of all the HVAC controls. I verify that all the blower speeds are working, the mode doors are sending air where they are supposed
to, the recirculation door is operating, and the temperature blend door is functioning.
When I operated the temperature blend control for the rear unit, I heard the unmistakable "clicking" of stripped gears in
the electric actuator. OK, this could very well be the cause of the "warm air" complaint, so I made a note of it on the repair
order.
All the other controls were working normally, so I next set the A/C controls for maximum cooling to see if I could hear any
abnormal noises from under the hood, then headed for the bay.
By the time I got it in, cold air was already blowing hard out of the front center ducts. So far, it seemed like the basic
A/C system was working OK. But today was an exception to our warm winter, and the outside air temperature was in the low 50s.
More complete testing was in order before I could conclude that the system was working as well as it should. And so far, I
didn't hear the noise the customer was complaining of.
In a heated bay
Once inside, I opened the hood and connected my gauges. I always allow a few minutes after shutdown for the system pressures
to equalize, and then take a look at the system pressures with the A/C and engine off. This "static" pressure can give you
an idea of the system's state of charge and the actual temperature that the condenser is "seeing." It will also let you know
whether your gauges are reading accurately: The low and high side gauges should be equal under these conditions.
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