Re: [DMCForum] Clicking noise behind passenger seat when A/C on
From: "Walter Coe" <Whalt@xxxxxxx>
Date: Mon, 8 Nov 2004 16:23:51 -0500
Derek,
Sorry this is so long, but it takes a lot of words to
explain what to look for:
Clicking coming from the relay compartment should be
expected because relays make a clicking sound when they
change state. But in your case since you seem to notice a
change in normal operation, you should consider how often
you hear the click and determine whether or not it is a
relay or something else.
Like Rich said, the click is most likely the one for the
radiator fans. They cycle with the compressor (when the
aircon is running, of course). They also should cycle
according to the cooling fan thermal switch (what is often
incorrectly called an 'otterstat' or 'otterstadt'). When
the engine is hot enough, the fans stay on whether the
compressor is cycling or not.
When the fans cycle according to the compressor, this can be
as often as every 4 seconds or take as long as 40 seconds or
more. So there are several things to consider when
evaluating the cycle time. The best thing to do is hook up
a manifold gauge set to the high & low sides and see what is
going on. If you cant do that then here are some general
guidelines:
At idle on a warm day, say 80F for example, with the blower
on high and the mode switch on MAX or NORM, the compressor
should cycle on for about 40 seconds at a time. But this is
a very coarse guideline; your mileage may vary. If it takes
20 seconds or less then you are most likely low on
refrigerant. If it runs continuously then perhaps it is a
very hot day or you have other problems like a miss-adjusted
low pressure switch.
With the hand brake on and transmission in park or neutral,
move the throttle in the engine compartment with your hand
revving the engine up to around 2500 RPM. It should cycle
on for around 7 seconds at a time. 4 second intervals could
be normal for a cool day or you are low on refrigerant.
Longer than 7 second intervals could be normal for a very
hot day or you have a miss-adjusted low pressure switch.
NEVER adjust a low pressure switch for 'optimum' cycle time.
You cannot make this adjustment without a manifold gauge
set.
Seeing the compressor cycle should be obvious when looking
at it. When off, the pulley slips. When on, the whole end
of the compressor turns with the pulley. You should hear
the radiator fans cycle with the compressor unless they are
already on due to the thermal fan switch sensing that the
engine is hot.
------------------------------
Now for a change in subject:
Maybe the click you hear is not the cooling fan relay.
Maybe you hear the cooling fan circuit breaker tripping &
resetting. Depending on your current configuration, this
circuit breaker may be bypassed. In this case you, of
course, wont hear it clicking. Put your finger on it to see
if it is getting hot, but be careful not to burn your
finger. It is one of the two circuit breakers mounted on
the forward wall of the relay compartment. One is for the
blower. The other is for the cooling fans. If either is
original or installed backwards, they may get hot & trip.
When they do, they can click rather loudly. It isn't always
obvious if they are installed backwards because the 'BAT' &
'AUX' terminals look the same. You have to read the fine
print next to each terminal to see which is which. Electron
flow should go from the AUX terminal to the BAT terminal. I
dont remember the proper wire colors without looking at a
car. And even then the wires could be burnt or repaired
with the wrong color.
Another thing you could hear clicking is the compressor
itself cycling. You wont hear it from the relay compartment
but rather coming from generally behind you while driving.
If you hear it clicking loudly, this indicates that the
system is low on refrigerant oil and is in the process of
seizing up.
> I'm not the A/C god here. It would be a good idea to
confer with Walt
> to make sure I'm not talking out of my tailpipe.
{Walt sits at his computer gloating with a big grin.}
Back to the Home of PROJECT VIXEN