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Vehicle problems that change without notice

The last thing we expect sometimes is the first cause that comes to mind.
Wednesday, December 31, 2014 - 08:00
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To Drive For a Year
The foreign exchange student who bought this car at the local GM dealer got it for a pretty decent price to drive for the year she’ll be here. The A/C was inoperative and the “LOW COOLANT” message was constantly displayed on the message center, but other than a couple of burned out stop lamp bulbs, this 1998 Buick was in pretty good shape.  We gave the car a good once-over right at the end of that work week, checked the coolant concentration and the availability of a coolant level sensor and then attacked the A/C for a prelim.

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We drew the air out of the A/C system because it had gone completely atmospheric since the last time anybody had injected any cold gas. Because she had been told when she bought the car that the A/C was leaky, we were surprised that it held 30 inches vacuum as good as it did. Next, because were almost out of time that week and she needed the car for the weekend, we injected some UV dye along with the refrigerant charge, felt it blowing cold and let her take the car with instructions to bring it back the next week for a follow-up.

When the Buick returned the following Monday, the “LOW COOLANT” message had been joined by a “TRUNK AJAR” message and the A/C’s refrigerant charge had mostly gone away. We replaced the coolant level sensor and took care of the Low Coolant message, but the Trunk Ajar warning remained.

As for the lost refrigerant, our black light lit the bottom of the A/C compressor up like it was radioactive (no surprise on one of these), and so we recovered the 0.3 pound of refrigerant that hadn’t yet leaked out and followed up with a 150 pound dry nitrogen pressure test. There were bubbles between the compressor housing shells, so we replaced the compressor, the orifice (which was clean) and the accumulator.  We drew the air out and charged the system, ready to feel nice cold wind at the register, but the compressor wouldn’t even engage. While we were investigating that, one of my guys noticed that the temperature needle was dangerously near the red line and the cooling fans weren’t working either. The loss of compressor operation, the dead cooling fans, and the trunk ajar message had all come about over the weekend, but none of these symptoms had existed during our previous service.  Developments of this nature always feel like a smack in the face, especially when the customer was expecting the car back that same day without a hitch, and inoperative cooling fans is an engine-destroying hitch!  One simple problem had been replaced by two larger problems that required stronger troubleshooting techniques. 

I put a couple of guys to work on that trunk ajar message while we began to gather data on the A/C no-engagement and the unresponsive cooling fans, but all they found was a normally operating trunk ajar switch, along with good voltages and circuits, so we closed the trunk and put that trunk ajar concern on the back burner.

Holding the Car
I had to call the owner and explain that we couldn’t release the car, primarily because of our concerns that she might damage the engine sitting in traffic with fans that wouldn’t spin. Investigating the fans for opens using my test light method, I typically remove the relay, find the terminal feeding each fan, connect a test light between B+ and each terminal and it should light up. Then I slowly turn the fan in question and watch for the light to go out. If it ever does, the fan must be replaced  Both of these fans passed that test. I did notice that at some point in the vehicle’s history one of the three fan relays had been replaced.

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