I have an older janitrol heat pump 240 volt. I know my transformer is bad.
However it's an older one with one 1 black wire built in. The rest of the wires
connect to it with spade clips. The one black wire plugs into power supply.
Another red wire comes from power source and plugs into transformer. On the
other side I got a ground wire plugged in, another wire plugged into a relay of
some sort, and 2 more wires plugged into the t-stat wires. New t-stats have 4
wires coming off one side. I'm assuming I use those 2 for power coming in. Cap
off other 2. On other side I have 2 wires coming off at 24 volts but I need 3.
Any idea or help would be great.
On Fri, 08 Jan 2016 23:44:01 +0000, Brokedown Palace
The compressor runs at 240. That doesn't mean the control circuit
does. It's probably 120.
If you expect to find a transformer with the same wires and spade
lugs, you might find one at a furnace supply store, in person or on
the web, if you provide the furnace make and modle.
Otherwise you'll be wasting your time to look for wire connections
that look like you have now. The wire connections are not what
matter. It's the primary voltage, the secondary voltage, and the
output amperage available that matter.
So are you saying that the secondary of the transformer is putting out
24 volts? If so, on what basis do you say at the top that you know
your transformer is bad?
Are you saying there is a center tap on the secondary?
Do you have a voltmeter? Have you used one before? Do you know how
electric circuits work? If you've never used one before you should
do some reading about electrical circuits, voltage, resistance,
amperage, AC, DC. If you're not willing to do this, consider calling
After you do this, you should measure the voltage at the primary of
the transformer, the side with only two wires. Be sure to put your
meter at 250 VAC or higher to start off. Then you should measure the
voltage between each pair of two connections on the secondary of the
transformer, the side with 3 wires. That is, if the wires were
labeled A, B, and C, measure and write down the voltage between A and
B, B and C, and A and B. If you measure right at the transformer or
at the end of wires coming straight from the transformer, the voltages
will be AC. And though you should start with the meter set at
200vac or so, when you see that the voltage is only 24 or less, you
can change the range of the meter to anything 25 volts AC or higher.
If it has 24 volt output, I'd be very surprised if the center tap is
Once you've made your measurements, turn off the power before you
touch anything. There are probably two breakers, one double one for
the 240 and another one for the 120. Turn them both off. And the
wall switch too if there is one.
But if the transofmer is actually no good, unless the rating or a part
number is stamped on the transformer, it will be hard to know the
amperage needed. I'd say that any transformer the same size or bigger
is likely to work fine. All they have to do is power the control
box, the thermostat, and the contactor at the compressor. In my
case, the HVAC store where I was didn't have the very same size
transformer so I bought a bigger one and mouted it elsewhere in the
cabinet, connecting the 5 wires with longer wires than were used
before. FWIW, the first transformer failed 6 weeks after I moved
in, when I had 4 guest from out of town The second one was still
working 32 years later when I replaced the whole control unit.
It might help to provide the model number of the unit. And, to do a web search
before posting to locate any relevant documents (so those folks who might be
inclined to help wouldn't be discouraged by having to resort to Ouija board...)
How about some idea as to the likely *function* the xfmr is performing?
Start with an estimate of its physical *size* (from which an estimate
of it's power handling capacity can follow!)
A photo along with a sketch of any wiring connections you've observed
traced would also be a big help ("picture... thousand words... etc.")
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