I have dual-zone York central air, two independent, but identical systems, 220V, with a dual pole contactor. While changing my blower fan on the outside condenser unit, I noticed that one unit’s compressor was wired different than the other! There are 5 wires coming from the compressor, all black, and unmarked. The only distinguishing difference is the wire gauges.

Unit 1:
Two heavy wires that connect to the switched side of the contactor, one wire per pole.
Once medium gauge wire connecting to the capacitor (other side of the cap connected to one pole of the switched contactor side).
Two lighter gauge wires, one each going to the UNSWITCED HOT side of the contactor. So these wires always are energized, even if the contactor is off, but the compressor does not run if the conntactor is off.

Unit 2:
Same as unit one, except both of the light gage wires go to SAME pole of the conntactor, one on the switched side, the other on the hot! In other words, these two wires “short together” when the connector actives, unlike Unit #1, (which has these two wires on opposite and are always hot poles).

Unit 2 does not seem as efficient, and my instincts tell me that Unit 1 has the correct wiring.

Some questions:

Which Unit is wired right?? My guess is #1

What do the lighter gauge wires do, as both systems do work, despite the wiring differences? Shouldn't only 3 wires be needed to run a 220V compressor?

Assuming Unit #1 is wired correctly, does it matter which of the light gauge wires go on which pole? How do I know which is which if I have to rewire unit #2, since they are not marked and of the same color and gauge…Since its AC current, I believe it doesn’t matter, but want to confirm.

Much thanks in advance.

Most compressors have a heating element that is on all the time. It is to protect the compressor from starting up when it is cool enough for there to be liquid Freon in the compressor.

Likely you are right, #1 is correct, and you should fix #2 the same way. If you are still having some cool morning, you might check the compressors when they haven't run for a while and find #1 warmer than #2.

You can defeat the heater over the winter by throuwing the breaker, but must hve it on a day or two in the spring before using the unit.

Labman, thanks for the quick reply! That makes sense, as the extra wires didn't seem to effect the system operation. How much power do these compressor heaters typically draw? I live in Texas, so maybe I should just disconnect both heaters for the summer to save a little electricity, and improve the system efficiency (why heat the compressor more than needed)? About how “cold” does it have to be outside before the compressor heater is needed?

BTW, this is a 15 year old system (but well maintained by myself), and I assume it’s been wired like this since day-one, so it looks like the heater disconnect didn't cause any obvious damage. I checked temp differential on this unit last night: 22 deg difference in air temp (input duct vs output), which I think is pretty good.

Thanks again, you know your stuff!!

I knew the answer to your first question, but not the new ones. Since your second compressor survived all these years without the heater being active, apparently it is not too important in your part of Texas. You could check the resistance of the circuit and calculate the amount of power used. Even a small load adds up 24/7.

Labman:

I thought you would like to know what the power consumed by my compressor heaters is, to add to your vast knowledge base!! The resistance is 600 ohms, so that’s 100 watts EXACTLY to a few decimal places at 245V (245x245/600)….. Wow, 200W being consumed 24/7, so the two compressors use an extra $15 total per month, even if the AC isn’t running at all. That’s $180 per year, and $2700 dollars over the 15 year life of the compressors so far.

OK, it was really less, since only one heater was working, and electricity was a lot cheaper before deregulation, but you get my point….What do you think of the idea of running the heater off 120V, so it only draws 25W? I could always run an extra neutral wire if needed.

It might be a good compromice for in Texas. Likely they sell the same design in Minasota too.