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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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My weather master thermostat just went blank, we just got

Customer Question

Hi my weather master thermostat just went blank
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: we just got back from vacation so not sure
JA: Do you plan on doing the work yourself?
Customer: depends
JA: Anything else we should know to help you best?
Customer: how to diagnose the issue would be helpful - what does it mean when the thermostat just goes blank? can I open it up, is there a battery or is it tied directly to the AC unit
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the HVAC Technician about your situation and then connect you two.
Submitted: 4 months ago.
Category: HVAC
Expert:  Phil replied 4 months ago.

Hello, you can pry the thermostat from its sub base that is screwed to the wall using a kitchen knife if you are gentle.

then if you see an R terminal and a C terminal use a volt meter to check for 24vac between those two, if you get 24v, replace the batteries again, clean the terminals while you have the batteries out... then if the screen is still dark, the thermostat is most likely bad, 98% chance.

IF you have no voltage between R and C, the problem is inside the furnace, a bad transformer, I will step you through a diagnosis if you have some tech skills and want to take the time.

Customer: replied 4 months ago.
No voltage going to thermostat but there is to the AC unit.
Expert:  Phil replied 4 months ago.

Thanks, there is a wiring diagram inside the furnace blower service door, send me a close up photo of the diagram, very well lit, and exceedingly well focused.... I will mark it up with trouble shooting instructions and coach you from there.

Include a photo of the printed circuit card that shows the thermostat wire connections to it.

Use the paper clip icon at the right end of the tool bar or the attach files link to the left of your send button to get me the pictures.

We can go from there.

Customer: replied 4 months ago.
There wasn't a diagram but attached what looks like specs for furnace. Will check what is on the AC unit.
Customer: replied 4 months ago.
Attached is an image from the AC unit. Hope this helps.
Expert:  Phil replied 4 months ago.

Thanks, ***** ***** diagram is great. I am marking it up with trouble shooting instructions now.

Expert:  Phil replied 4 months ago.

check for 230v power to the unit, that is *across* line 1 and line 1

Next do steps 1,2 and 3 below, let me know what you can discover

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