My 1986 Lennox AC compressor unit just stopped running, the fan isnt
running and no noise comes from the unit, I reset the breakers and the
thermostat is the old round analog Honywell, its calling for cooling.
Ive never worked on this but is there anything I can test with a V
meter before I call a pro. 3 weeks ago I lost all freon from a big
leak and had it fixed, all has been fine until today. I would think at
least the fan would run.
When this happened to my 1991 Lennox, it was the timing board. That
particular board delayed turning the thing on for 5 minutes once it
was told to by the thermostat. This was to make sure the old mercury
therms had time to settle and prevented on-off-on-off. The tech said
it was pretty obvious that the board burned out. One possibility?
If there was a thunderstorm, a voltage spike could have blown the
run capacitor. If your air handler fan doesn't run, it's a power
problem there because the 24 volt control voltage comes from the
furnace/air handler. Without the 24 volts AC, the condensing unit
where the compressor is will not come on. If you can push in the
insulated contact carrier on the condenser contactor and the fan
and compressor run, you'll know it's not getting control voltage
from the furnace/air handler.
On Aug 22, 10:01 pm, The Daring Dufas <the-daring-
What does the condensor contactor look like where do I find it, I
wonder if the tech left a wire loose since it seems like it just has
no power. I do know I dont think it was installed with proper gauge
wiring , Its about a 60 ft run of 2 pieces of 10 ga and it rattles in
the pipe and at the breaker on turn on. All these years of rattling
could have loosened something.
It's the only (usually) relay-looking-gizmo in the outside unit. It supplies
power to both the fan (120) and the compressor (240). If both are not
working, the obvious culprit is the only thing they have in common - the
That said, it could be the relay itself is broken (fried, etc.) or the
voltage that activates the relay (24V) is missing.
If the relay, they're not TOO expensive and, if your hand fits a
screwdriver, you should be able to replace it. Label the wires - taking
several pictures is better - and take the old one to Graingers. Say "gimme
one like this".
Remember to wear eye and ear protection when working around electricity and,
um, er... one other saftey precaution, but I forget...
Yep. It's either not getting the 24v OR unable to use the voltage cause the
relay itself has given up the ghost, taken a dirt nap, singing in the
heavenly choir, or passed this way only once to brighten our lives, provide
endearing memories, and let us chill.
I've never heard of a wire or a breaker "rattling". The freon lines
on some units can be noisy and that might be what you hear.
You can check for 240vac at the unit. It should be easy to trace to
the contactor (a big relay). The contactor is a 24vac activated relay
that supplies 240vac to the entire unit. The inside half sends the
24vac. It is possible to manually activate a contactor by pushing it
down carefully with something. The compressor and it's fan are both
activated by the contactor. If there are any additional controls such
as the startup delay board they will most likely be on the 24vac
side. Both the compressor and the fan will use run capacitors but
they may be combined in a single can. Ther may also be a start
capacitor on the compressor. Since nothing is running I doubt it's a
I can hear the wires "Rattle" inside the conduit and the breaker on
the main panel makes a zip noise when it powers on, I bet it should
have been a larger gauge but they had no more room in the conduit. I
mentioned it to them on install and they said 'its ok", but I know it
would have been rejected by an inspector. I didnt get a permit or an
inspection for the install, In 96 I didnt think permits-inspectors
were a help. Thats why I wonder is I have any power since nothing
works, but im no electrician.
It's not unusual for wires to move or rattle inside a conduit even if
the wire is properly sized for the load. The starting current of an AC
compressor can easily be several time the run current of the whole unit.
Wires can and will dance under the right set of circumstances.
I only have four decades experience in the field and I see it all
the time. In an industrial environment I've come across it a lot
where there are a numerous high current starting loads for motors.
The wire can actually change length under heavy load. I've seen
insulation rubbed of a wire because of this movement. The OP can
hear the #10 wires jump inside the conduit when his AC unit stars.
When you get your PhD in know-it-allogy, come back and call me names.
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