Some background, which may or may not be pertinent:
Periodically (a couple times a year) I've had times when I'd receive
an error message on my thermostat, indicate a problem with
insufficient 24 voltage to it. This happened yesterday, after a pretty
bad rain and thunder (lightning) storm. I'm thinking it's related to
wetness, as it has always cleared on its own after a bit. Yesterday,
it did the same working again after an hour or so.
I've had to replace the contactor on an almost annual basis. Not sure
why this is, why my a/c is apparently cycling too often, but that's
for another time.
Today (while dealing with an unrelated(?) problem with my electrical
water heater (still figuring that out), I noticed that there was NO
power to my thermostat. As opposed to an error message, there was no
power. I twisted the R & Y wires together, but still no a/c.
I was thinking it could be the 24 volt transformer, and it's simply
been going bad for awhile? Would it be the transformer that's attached
to the circuit board, and has a black wire going to the contactor?
I manually pushed in the contactor and the condensor turned on, as
long as I held it in. BUT, after about 1:30 to 2 minutes of holding it
in, it shut off while I was still pressing the contactor firmly in.
Still not a good connection?
Any thoughts?! Thanks.
Thanks; I found it.
Okay, if indeed it sounds like there are any number of possibilities,
then maybe I will. Any chance it's simply a bad transformer and
replacing it is $10?
I realize I'm not very knowledgable, but that's why I'm here. And it's
saved me a bunch in the past, as I"ve replaced my own contactor a few
times, my blower motor once, and the first time the "professional"
replaced the contactor he even hooked it up wrong. I'm not saying
that's the norm, of course, and that there isn't a time and place for
calling in a pro (and perhaps this is that time), but as long as I'm
safe about it, I figured many of these things are do-able oneself.
You have to think like a doctor, take the Hippocratic oath to do no harm,
then proceed. Check the output terminals or wires of the transformer for 24
volts. If you have it, you've probably got an open circuit in the low
voltage wires. If you don't have it, check the line voltage input, probably
240 volt. If you have line voltage, but no low voltage, change the
transformer. It's probably a 40VA unit. Also, be sure the low voltage wires
are at least 20 ga, preferably 18 gauge, and not 24 ga. telephone wire.
Thanks much. Will check the 24 volt. In the meantime, any thoughts on
the contactor issue? That when I held it in, after about a minute and
a half the condensor shut off? Would that indicate a contactor
problem, or anything else?
Okay at the risk of being seen as a dolt, I figured it out. What with
the prior 24 volt intermittent problems, it took my mind right to
It was the simple overflow cutoff, or whatever it's called, wherein
the condensate in the air handler, if it backs up too much it trips a
shut-off in some pvc that comes out of the tray. Shuts the power off.
When I forced the system on by closing the contactor, it worked (I'm
trying to recall here) until the system once again recognized the
overflow event and sent a signal to shut it off again?
Anyway, NEXT time: #1) check overflow valve - which, btw, I first was
exposed to several years ago.Turns out it was the contactor then, but
the kind a/c guy hooked it up correctly and explained it to me then.
Just forgot about it. Arghh...
Thanks so much, all! Still learned a lot more. AND, why is it no one
in all the walk-through's and trouble-shootings I looked at on the
web, that no one mentioned this? It should be step #1, even if one
doesn't have it, in case they do.
That is one of the problems in trying to diagnose an issue without being
there. There are all manner of possible safety devices that could cause the
system to not work. When you hold in the contactor, the condenser should
run. I'm not in that business, but my guess would be that some internal
cutout may have shut it down due to high pressure since the blower was not
If you're electrically minded, you may very possibly have
the skills to fix it, yourself. Been a while since I bought
a transformer, but it was over ten clams. You may very
possibly have the skills to check and see if it's a bad
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.