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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Honeywell RTH 8500D. I usually shut it down (off)

Customer Question

I have a Honeywell RTH 8500D. I usually shut it down (off) for the summer. In past years the thermostat would still show the time and temperature, humidity etc. Now it is blank. I get to DC voltage reading from any of the wire connections. This thermo controls a Coleman Echelon 9.C series gas furnace
Submitted: 2 years ago.
Category: HVAC
Expert:  airheatman replied 2 years ago.
Hello. My name is ***** ***** I'll do my best to help. Let's get started and see what we can do.We should be getting 24volts AC (NOT DC) between R and C. Check that and let me know.
Customer: replied 2 years ago.
Voltage is fine
Customer: replied 2 years ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from yo. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  airheatman replied 2 years ago.
Have you replaced the AAA batteries also?
Customer: replied 2 years ago.
This unit doesn't use AAA is a Lithium Battery and there is no reference in the owner's manual for battery replacement.
No further discussion, thank you.
Expert:  airheatman replied 2 years ago.
Here is the manual I have. The triple A batteries are referenced on page 59:
Batteries shown here: