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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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My Trane A/C unit has stopped running. Temp inside is 81. I

Customer Question

my Trane A/C unit has stopped running. Temp inside is 81. I have the thermostat set at 74, but it says "wait" instead of kicking on the A/C unit the way it normally does.
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: I think it's probably a larger HVAC issue. I replaced the batteries in the thermostat recently and I have no reason to believe the thermostat is not working. The thermostat eventually clicks as if it's turning the system on, the message changes from "wait" to "Cool On", but the unit does not start working.
JA: Do you plan on doing the work yourself?
Customer: I would like to if it's something I can do.
Submitted: 9 months ago.
Category: HVAC
Expert:  Phil replied 9 months ago.

Hello, the odds that it is a larger problem than just the thermostat are in the 98% range.

Expert:  Phil replied 9 months ago.

Tell me a lot about your electronics skill sets so that I can coach you most appropriately, it will be a2 to 4 hour long session if you have the skills. If you do not have skills in that range tell me which direction you are from the center of the nearest city and I will see if I can find a well rated service outfit in your area.

Customer: replied 9 months ago.
I don't have official training in electronics, but am pretty good at DIY projects with good instructions. For example, I've installed stereos into my car, install light fixtures, bathroom and kitchen faucets and ceiling fans on my own and am very good with computers.
Expert:  Phil replied 9 months ago.

Thanks, ***** ***** case send me a close up. well lit, and exceedingly well focused picture of the wiring diagram glued to the inside of the blower access door on your furnace. and a photo of the printed circuit card mounted on the blower showing the *thermostat* wire connections. Use the paper clip icon at the right end of your tool bar for that, or the attach files link to the left of your send button.

We can go from there, you will need a multi meter.

Customer: replied 9 months ago.
I've attached the pictures you requested.
Expert:  Phil replied 9 months ago.

Thanks, ***** ***** need a photo of the wiring *diagram (that's a sheet of paper) glued to the inside of the blower access panel.

For now fit a jumper wire between R and Y... if the outside unit runs the problem is with the thermostat or its wiring.

If the outside unit does not run set the thermostat to cooling and down to 60F and measure the voltage between Y and B/C

If you get24v read then the problem is with the outside unit.

Customer: replied 9 months ago.
OK. I attached two files and the file named IMG_9748 is a picture of the wiring diagram that was glued to the inside of the blower access panel. If this is not what you need, I'll need a further description to look for the diagram that you need. this was the only diagram on the inside cover of the blower unit.Regarding the jumper wire instructions. Could you describe in more detail where I'll find the R and Y connectors you mentioned? Is this on the circuit board of the blower unit or is it on the circuit board of the thermostat?
Expert:  Phil replied 9 months ago.

Those letters R, Y and C are among the terminal numbers on the printed circuit board that you sent a picture of where the thermostat wires attach.

The two wires that control the outside unit are attached to Y and C

Customer: replied 9 months ago.
By the way. I have an identical Trane touch-pad thermostat for my downstairs unit which is operating correctly. I removed the face of both thermostats and swapped them. The downstairs A/C unit continues to work after I install the thermostat that was originally upstairs. The upstairs A/C unit continues to NOT work even after I install the thermostat that was originally downstairs. I think that likely confirms that the thermostat is not the problem. Would you agree?
Expert:  Phil replied 9 months ago.

Yes I agree, as I said at the opening the odds that the problem is elsewhere, not in the thermostat, are in the 98% range... had you seen that?

Expert:  Phil replied 9 months ago.

Have you checked for voltage between Y and C as mentioned in my 11:01 remark?

Diagnosis involves doing those tests

Customer: replied 9 months ago.
I'm attaching a photo of how I connected my multi tester to Y and B/C and a second picture showing the reading I got on the multi-tester. I'm not experienced with using the multi-tester a great deal, so I wasn't 100% about which setting to use. I adjusted the dial and took a reading on each setting. This was the only setting on which I received a reading that was not 0 or pegging the meter to the right. I'm not sure if I did this correctly.
Expert:  Phil replied 9 months ago.

Thanks for the pictures, you have your meter set on OHMs not volts, if there was voltage there you can damage the meter by doing that. This is tricky business, the community college training is 2 years, 20 units a semester, then 4 years working under a journeyman...

I am able to offer you a 6 hour training course that will enable you to do those checks correctly without damaging your meter, its a bit arduous and will require some study on your end, or if you want to tell me which direction you are from the center of the nearest city I can locate a well rated service outfit if there is one in the area.

Customer: replied 9 months ago.
I set my thermostat at its lowest setting (65 degrees) and used each of the voltage settings on my meter first to attempt to get a voltage reading. The meter did not move while using any of the voltage settings. Does that tell you anything? You mentioned above that if I had a reading of 24v the problem is with the outside unit. I'm not sure what it means when you get a reading of 0.Since we're pretty sure it's not the thermostat, and I seem to be getting a 0 voltage reading, is there anything else I can do to troubleshoot? It will not be feasible for me to take a 6 hour training course.
Expert:  Phil replied 9 months ago.

If you are using your meter correctly. (triple check it in a wall receptacle) a zero volt reading between C and Y indicates that the thermostat is not working correctly... you can double check that by fitting a jumper wire from R on the terminal strip to Y on the terminal strip.... if the outside unit comes right away or after 5 minutes, then the thermostat is the problem