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Phil, Mechanical Engineer
Category: HVAC
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Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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We have two Trane XR90 units in our business and one is not

Customer Question

Hi - We have two Trane XR90 units in our business and one is not powering on. I have tested the circuit board and transformer by swapping from the working unit to the non-working with no luck. What else could cause this? All breakers are working and power is coming into the outlet that the unit is connected to.
Submitted: 3 months ago.
Category: HVAC
Expert:  airheatman replied 3 months ago.

Do you have a meter where we can do some step by step troubleshooting?Also give me full model from label inside unit

Customer: replied 3 months ago.
The model # is TUX1D100A9601AB. I have a standard multi-meter.
Expert:  airheatman replied 3 months ago.

Lest go one step at a time. With door switch held in check between Line-H black and white LINE -N for 120 volts.Then from XFMR-H black and XFMR-N white and make sure we have 120 volts.

Customer: replied 3 months ago.
Ok, dumb question but what setting should I have my multi-meter set to?
Expert:  airheatman replied 3 months ago.

AC volts. Lowes setting above 120 (Probably will be 200)

Customer: replied 3 months ago.
Ok I'm not getting any reading on either. All zeroes, just changes to negative zeroes when connected.
Expert:  airheatman replied 3 months ago.

Try meter in a known powerlocation like a receptacle to make sure we have it set right and meter is working

Customer: replied 3 months ago.
Just tested an outlet. Reading 122 so seems to be working.
Customer: replied 3 months ago.
Should I be testing the pins with the wires connected or disconnected? Sorry, not an electrical whiz...
Expert:  airheatman replied 3 months ago.

Wires connected

Customer: replied 3 months ago.
ok looks like 120 on both
Customer: replied 3 months ago.
ok maybe not
Expert:  airheatman replied 3 months ago.

If 120 on both Next lets check for 24v from transformer back to board.

If not120 on both let me know

Customer: replied 3 months ago.
not 120 unless I'm just not making a good connection. neither gives a reading above 12. the receptacle it is plugged into is 120.
Expert:  airheatman replied 3 months ago.

Lets check at the disconnect supplying power to unit. (Both in and out)

Customer: replied 3 months ago.
sorry not sure what you mean by disconnect
Expert:  airheatman replied 3 months ago.

Main power coming in.Usually a disconnect or switch outside on unit

Customer: replied 3 months ago.
the unit is in a drop ceiling and is connected to a receptacle in the ceiling with an on/off switch. I checked that receptacle and it reads 120.
Customer: replied 3 months ago.
i you mean a switch on the unit itself I will have to see if I can find it
Expert:  airheatman replied 3 months ago.

Yes also check the actual circuit breaker in main panel that provides power to furnace

Customer: replied 3 months ago.
The power to the unit runs from the receptacle to a condensate pump which is hardwired into the unit. The circuit breaker has been tested and is good.
Customer: replied 3 months ago.
never mind. the power I am looking at is the power to the pump.
Customer: replied 3 months ago.
apparently when you power off the pump the unit turns off for safety.
Expert:  airheatman replied 3 months ago.

OK locate the wires where they come into the unit.If they are connected with a wire nut, check there. Now one note here. While doing these tests, you will have to have door switch held in to have power where I told you to check, (L1 and Neutrals). If you did not have switch held in, hold in and re check.

Customer: replied 3 months ago.
I do not see a disconnect. When tracing the wiring it looks as if it runs directly from the circuit breaker panel.
Expert:  airheatman replied 3 months ago.

Did you have door switch in earlier?Now one note here. While doing these tests, you will have to have door switch held in to have power where I told you to check, (L1 and Neutrals). If you did not have switch held in, hold in and re check

Customer: replied 3 months ago.
the door switch was taped down
Expert:  airheatman replied 3 months ago.

OK find where the wires enter the furnace and check here. If we do not have 120v at the board we are loosing it somewhere between board and circuit breaker.

Customer: replied 3 months ago.
Ok, there is actually an electrical box that runs from the same power as the receptacle that the wiring come in from. It looks like the wiring runs directly to the board from the metal box.
Expert:  airheatman replied 3 months ago.

Can you upload a picture?

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