Condenser power draw question

[supratreo]

hi, have a question for you guys more knowledgeable than I.
i installed a energy monitor on my main panel about 2 years ago and since then i've noticed that 1 of my 2 condensing units is constantly drawing current. its only .3A on each leg but its 24/7/365.
i used my amp clamp to see where it might be going but i don't see anything drawing power. fan motor is completely removed as i was cleaning the unit and compressor is not drawing anything. i checked the contactor and its open but i'm getting ~1V on the top. i'm thinking the contactor is bad but i'm trying to figure out how i would be getting any voltage if the contacts are open.
i'm about to throw a contactor at it but i want to make sure thats the problem and WHY its doing what its doing.
only other components in there are start and run caps for the compressor, a start cap for the fan motor and a relay box.

thank you

 

[BillK]

Probably the heater. I dont know if they are thermostatically controlled or not. Are both units the same ? Model numbers ?

 

[fitter30]

Crank case heater. Take a pick of the wiring diagram. Probably wired with a 1 pole contactor. Where the leads for the heater is across the contactor contact when contact is open heater is on, closed it is off compressor is running. Heater keeps the oil warm and refrigerant out of the oil.

 

[PoorUB]

A lot of the compressors use the motor windings as a heater. If you look at the wiring diagram there is power across the capacitor and motor windings when the unit is off.

 

[supratreo]

thank you guys, i'll check that out and get you the diagram. its a Trane xp13 but i'll get the exact model.
i have another unit next it to, just smaller, that never has a current draw thats why i thought this was abnormal.

 

[Dagny]

I would like to see those diagrams

 

[wyliesdiesels]

thank you guys, i'll check that out and get you the diagram. its a Trane xp13 but i'll get the exact model.
i have another unit next it to, just smaller, that never has a current draw thats why i thought this was abnormal.

electrical diagrams would confirm whether theres a heater cycling

 

[supratreo]

sorry for the delay, heres the diagram. lmk if its hard to make out, i will try to find a copy online.

 

[PoorUB]

The diagram shows a "sump heater" that is one unless the compressor discharge line is warm. So it is on unless the compressor is running.

 

[wyliesdiesels]

yup looks like theres a heater

 

[supratreo]

thank you for the replies. i'll slap the unit back together. started getting hot here all of a sudden and should be in the 90s by mid week.

 

[wyliesdiesels]

thank you for the replies. i'll slap the unit back together. started getting hot here all of a sudden and should be in the 90s by mid week.

yup i miss winter already. im an hour south of you...

 

[American Locomotive]

0.3a @ 240v is 72 watts. 72 watts 24/365 is 630 kWh/year. Nearly $190/year to keep my compressor warm. Over the 15 years that system has been installed, it has cost the homeowner(s) a collective $2850.

Talk about lazy engineering just leaving it on nearly all the time. I'd probably add a thermostat set to 65°F or so on that crankcase heater, but that's just me.

 

[supratreo]

yup i miss winter already. im an hour south of you...

so do i until its 40 degrees and dark at 4:30 lol.

0.3a @ 240v is 72 watts. 72 watts 24/365 is 630 kWh/year. Nearly $190/year to keep my compressor warm. Over the 15 years that system has been installed, it has cost the homeowner(s) a collective $2850.

Talk about lazy engineering just leaving it on nearly all the time. I'd probably add a thermostat set to 65°F or so on that crankcase heater, but that's just me.

thats a great idea. would there be any downside to it? i had the breaker off all winter thinking it would get around to checking on it but here i am mid april finally doing it. i could pull the breaker every winter but an automated system like a t-stat would be so much better.

 

[BillK]

It looks like the sump heater is wired through a thermostatic switch. It is marked TDL and is just to the right of the heater in your wiring diagram. Good bet it has failed in the closed position. Now whether is is replacable or part of the compressor is another story.

 

[BillK]

trane crankcase heater thermostat - Google Search

 

[supratreo]

i did see that switch installed on one of the lines but didn't think to test it. by what others were saying i assumed it was normally closed and open when the line gets hot.

actually now looking at it, its supposed to be NC.

 

[BillK]

i did see that switch installed on one of the lines but didn't think to test it. by what others were saying I assumed it was normally closed and open when the line gets hot.

actually now looking at it, its supposed to be NC.

Should be easy enough to test with an ohm meter and a heat gun. I didnt look at the specs to see what temp it is supposed to open at. Make sure the one you are looking at isnt the "high temp" switch. Should be able to trace the wires to the sump heater.

 

[supratreo]

right but what i'm saying is that if its supposed to be NC then its doing its job.

 

[BillK]

right but what I'm saying is that if its supposed to be NC then its doing its job.

Only if it is colder than the temperature that it is supposed to open at. You said you had two units and the second one was not pulling any current. Is your other unit exactly the same ? If so check it and see if it is open or closed.

If nothing else look up the part number for the switch and see what the specifications are.

 

[supratreo]

no, forgot to mention but the other unit does not have a heater.

 

[PoorUB]

It looks like the sump heater is wired through a thermostatic switch. It is marked TDL and is just to the right of the heater in your wiring diagram. Good bet it has failed in the closed position. Now whether is is replacable or part of the compressor is another story.

And if you look closer the thermostat is on the dischage line of the compressor. If the discharge line is hot, and it will be any time the compressor is running, the heater shuts off.

 

[PoorUB]

no, forgot to mention but the other unit does not have a heater.

No small current draw on the other unit? I mentioned earlier they often run a bit of current through the capacitor and the motor windings when the unit is off. It acts like a crank case heater.

 

[supratreo]

no, the other unit is a little different and does not have a heater and has 0 draw when off.