MACS Monthly Newsletter - 2022 - SEP6

Why Did the Compressor Lock Up?
By Richard Hawkins, MACS Technical Correspondent
All too often when a compressor lock-up occurs, the
compressor itself is blamed for the lock-up. While it is
possible for a manufacturing defect to cause a lock-up,
there is usually a problem related to the service work
or a problem with the system that is the culprit (Figure
16).
limo company's manager was at the parts counter of a
facility that both sold A/C parts and had a top-notch
A/C shop. He was complaining about the compressors
being " junk " because another lock up had occurred. It
just so happened that the lead technician had come
to the parts counter to get a part and he happened to
hear the conversation.
The problem
He spoke with the limo company manager and got
Figure 16: When a compressor lock-up occurs, the compressor
itself is often blamed for the lock-up.
I have had a multitude of tech calls with shops over
the years about this subject and usually someone is
requesting a warranty because the compressor is allegedly
defective. When deciding to write about this
subject, I recalled a conversation I'd had involving a
Lincoln Town Car limo (Figure 17).
some more information about what had transpired and
then told him directly: " You don't have a compressor
problem. You have another problem with that system
and until you diagnose it and fix it, compressor lock
ups are going to continue " . The limo company manager
was " taken aback " a bit and replied in a bit of a forceful
way: " What do you mean I don't have a compressor
problem? If the compressor is locked-up, then there is
a problem, and it needs to be replaced. "
The technician explained to him that yes, the compressor
was locked up, but the fact that this had happened
so many times in such a short period of time
indicated that another problem with the system was
causing the issue.
At that point in time the limo company manager became
a bit more cooperative, and the technician was
able to get some additional information about how the
system was serviced and didn't detect any issues with
any of that. He was also able to speak to the driver of
the limo who had experienced the last two lock ups
and get information about when they occurred. In
both cases he had been driving back from a higher
elevation in the mountains where temperatures were
milder, and the compressors had locked up when going
through a valley.
The technician convinced the limo company managFigure
17: Lincoln Town Car limousine.
er to bring the limo over to the shop after they installed
another compressor for some diagnostics. A couple of
days later when the limo arrived at the shop, the technician
took the vehicle for a long test drive.
Initially everything seemed to be working OK. The
This limo had been through about five or six locked
up compressors in a period of about two months. The
September 2022
6
system was blowing nice cold air from the vents, and
it was cycling. However, after a while, a problem surfaced.
The air coming from the vents was much colder
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MACS Monthly Newsletter - 2022

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