MACS Monthly Newsletter - 2022 - SEP7

than normal and the system was not cycling. The technician
suspected a problem with the clutch cycling
switch or the clutch relay. To better determine what
might be going on, he got two test lights and made up
some long test wires. He then connected one of the
test wires to the wire powering the compressor clutch
and connected the other test wire to the wire running
from the clutch cycling switch to the clutch relay. See
Figure 18.
The relay was sticking in the on position and the
compressor would not cycle off when the clutch cycling
switch turned the power off to it.
After arriving back at the shop, the technician took a
screwdriver handle and gently tapped the clutch relay
and the clutch immediately disengaged. He removed
the relay, checked the pins on it to make sure there
were not any issues with them having overheated and
they looked OK. See Figure 19.
Figure 18: There is nothing " high tech " about test lights
and test wires. They can be very useful when diagnosing
electrical problems in circuits such as those powering a
clutch and controlling a clutch relay. They should not be
used on low amperage circuits with electronic components
in them.
He ran both wires back into the passenger compartment
and connected them separately to each of
the test lights and grounded them. Now it was time
to go for another test drive. This test drive went like
the previous one. Everything was working fine initially.
The compressor was cycling and when it did, both test
lights would turn off.
As soon as the compressor turned back on, both
test lights would light back up. After about the same
amount of time as on the previous test drive, the technician
detected that the compressor was not cycling.
The air from the vents had gotten extremely cold and
the compressor was running continuously.
However, instead of both test lights being lighted,
the one connected to the test wire running to the compressor
clutch was on. The one connected to the test
wire running to the wire connecting the cycling switch
to the clutch relay was off. That indicated the clutch cycling
switch was working but there was an issue with
the clutch relay.
September 2022
7
Figure 19: Suspect the relay is causing a problem?
Look inside and check the contacts! Most relays can be
opened with a small screwdriver, by gently prying the
cover from the base (usually two are needed, one on
each side). This relay shows evidence of burning on the
contacts themselves AND on the inside of the cover.
MACS Service Reports
Steve Schaeber
Steve Schaeber
Steve Schaeber
MACS Monthly Newsletter - 2022

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