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Unlocking the compressor lock up

By Richard Hawkins, MACS contributor.

This is part three of a series of articles on unlocking the compressor lockup.  If you have not read them, they can be found here.  Part 1. Part 2.

Last week’s article ended with the following statement:  “Check back in next week and we will cover another compressor lock up that I experienced. “This was on a vehicle that I owned, which was a 1995 Chevy Astro Van.  

When this van was about 4 years old and had about 150,000 miles on it, I drove it to Raleigh, NC which is about a two hour drive.  The ambient temperature was in the upper 80s to low 90s. As I approached Raleigh, I noticed the temperature inside of the van had increased a bit. Placing my hand near a vent, I also noticed that the airflow had decreased and increasing the blower speed did not increase the airflow much.

Suspecting that the evaporator had frozen up I pulled into a parking lot and raised the hood and looked into the engine compartment.  Sure enough, the inlet to the evaporator, the evaporator outlet and the accumulator all had a hefty coating of ice on them.

This confirmed my theory that indeed the evaporator had frozen up.  An “on the spot” diagnosis indicated that the problem was a clutch cycling switch which was stuck in the on (closed) position and would not allow the compressor to turn off. Even though the A/C had been running a considerable amount of time with the evaporator frozen up, there was no damage to the compressor unlike the case with the Town Car in the previous articles (more on that next week).  Please see picture # 1.

The scene under the hood of my van was very similar to the one in this picture.

I made a few phone calls to locate a clutch cycling switch as I intended to go ahead and replace it right then.  However, surprisingly nobody in the area had one in stock.  An order was placed for one and it took about 4 days to arrive.

In the meantime, there was quite a bit of driving to do.  I did not want to do without A/C, so I just manually cycled the compressor by tuning the A/C off and on with the switch on the dash.  That worked fine and when the new cycling switch arrived, I installed it and that fixed the cycling problem. Please see picture #2.

The clutch cycling switch on my Astro Van

Now let’s fast forward eight years and about 90,000 miles later: The van then had about 240,000 miles on it and the A/C still worked great.  I live in the south-central part of Virginia, and it can get pretty cold here in the winter (temperatures in the 20° F range are experienced frequently). 

However, sometimes in January or February, some rare 70° F days are experienced.   We experienced one of those days and I turned the A/C on to make it a bit more comfortable inside of the van.

After a bit of run time, the air coming from the vents had not cooled down any.  I stopped and raised the hood to investigate and could see that the compressor clutch was not engaged.  A bit of “on the spot” diagnosing found that there was a problem with the clutch cycling switch:  I made a jumper wire and plugged it into the connector which plugs into the clutch cycling switch to test the switch.   When the  A/C was turned on, the compressor clutch engaged and the system blew nice cold air.  Instead of being stuck in the on (closed) position as was the case in Raleigh, it was stuck in the off (open) position.

I was in a hurry and did not want to take the time to go get a new cycling switch and install it and was only planning to drive about 30 minutes.  So, I did something I should not have done.  I left the jumper wire in place and manually cycled the compressor as I had done eight years earlier and everything worked fine. I should have removed the jumper wire but forgot about it and left it in place.  Please see picture #3.

The jumper wire inserted into the clutch cycling switch connector. This is ok for testing purposes, but one should never be left in place for system operation.

Now let’s fast forward to about a week later and a sub 32° F morning with ice on the windshield:  I went outside, started the van up, turned the defroster on and went back inside and ate a nice breakfast.  After about twenty minutes, I came back outside, switched the defroster off and tuned the heater on and went on my way.

Check back in next week for the rest of the story.

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