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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Regan, when I went to turn on the A/C last night, the Honeywell thermostat's scree

Customer Question

Hi Regan, when I went to turn on the A/C last night, the Honeywell thermostat's screen was off (no power). I went ahead and replaced the batteries, which then turned on the display. However, the A/C will not respond to the thermostat.
Submitted: 2 years ago.
Category: HVAC
Expert:  Phil replied 2 years ago.
Welcome! We keep going until you have all of the information you need.[b/]. Extensive training & coaching also available.
Set the thermostat fan control to FAN ON... if the fan does not come on remove the cover of the blower compartment where the thermostat wires attach to the printed circuit card.
If there is a door switch on that cover, hold it in by hand and tell me if you see any lights flashing on the printed circuit board or not.
Next fit a jumper wire between R and G terminal on the thermostat wire connection strip and tell me if the fan comes on.
If not use a multi meter set on 120 volts and measure the voltage between R and the body of the gas valve. Tell me what voltage read you get.
If you need more exact instructions, take a close up, very well lit and focused photo of the wiring diagram glued to the inside of the blower service panel and attach it here using the 'attach files' link at the lower left of your reply box.
We can go from there.
Customer: replied 2 years ago.
Hi Phil,I tried the following:
- Turn fan to ON on thermostat = Nothing happened
- Fit wire between R and G = Nothing happenedAs an additional note, not even the fan on the A/C is turning on (not just a compressor issue). Attached is a picture of the thermostat and the wiring behind it for you to see.Look forward to hearing next steps from you.
Customer: replied 2 years ago.
PS: I don't own a multi meter, so I wasn't able to perform that test. Anyway, if you believe that its indispensable to resolve the issue, I'll go buy one.
Expert:  Phil replied 2 years ago.
Hello again, you will need a multi meter, a $30 one is idea, you might get by with a $15 one but its not safe on the outside unit, only a $30 is reasonably safe on the outside unit.
copy /paste that to your web browser
I think you have a 24volt power failure, bad transformer or 3 amp fuse on the printed circuit card.
we need to locate the cause for that.
Please attach a well focused close up photo of the wiring diagram glued to the inside of the blower service panel.
We can go from there.
Customer: replied 2 years ago.
I tried the local hardware store which didn't have a multi meter, so no luck there. I also wanted to note that this only started happening last night after the thermostat ran out of battery. Before that, it was working perfectly fine. Last night I changed the batteries when I went to turn it on and noticed the thermostat was off. After I changed them, the air conditioner wouldn't respond to the thermostat.Could you provide more info as to what is the blower service panel? I am not sure what I'm looking for and don't really see any panels on the A/C unit.
Expert:  Phil replied 2 years ago.
I need the brand and model number of the furnace or air handler that thermostat wires attach to, and about how old it is, and a photo of the unit take from about 8 feet away.
Customer: replied 2 years ago.
Brand and model are on the attached pictures. Also included the photo of the unit which should be around 8 years old.
Expert:  Phil replied 2 years ago.
That is a sophisticated ground water source heat pump. You should not be working on it unless trained in that technology, and you do need a multi meter.
Meantime you can remove both of the panels shown and take photos of the inside... and a close up of the printed circuit board that has the thermostat wires attached.
Look on the back side of each panel for the units wiring diagram. We can go from there.
Obey all of the warning labels you see on the outside and inside of the unit.
We can go from there. You still need to get a multi meter, these are very common items, tell me which direction you are from the center of the nearest large town or city so I can help you find one.

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