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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 Chromotherm III. My AC was working with no problems.

Customer Question

I have a Chromotherm III. My AC was working with no problems. The EM.HT LED started flashing and the AC quit. A flashing LED is not mentioned in the manual, I have not been able to find it mentioned with a Google search, and my local HVAC contractor has never seen this happen and doesn't know what it means. What's going on?
Submitted: 2 years ago.
Category: HVAC
Expert:  Brian HVAC Guy replied 2 years ago.
Hi I'm Brian and I'm here to help! On some heat pump/thermostat combinations the emergency heat light will light if there is a problem with the heat pump. A signal is sent from the outdoor unit to the thermostat typically on the L or F terminal of the thermostat. I have never seen one flash though. If you can provide me the exact model number of your Chronotherm III thermostat and the make and model number of your heat pump outdoor unit, I may be able to shed some light on this for you (no pun intended :) ) Thanks, -Brian
Customer: replied 2 years ago.
I don't see a model name or number, just that it's a Chronotherm III for heat pump systems. I did find a number ink-stamped on the inside of the case (T8611M70081 9648). Is that it? The heat pump is a Water Furnace ATH057D110CLS #NA0038.Tom
Expert:  Brian HVAC Guy replied 2 years ago.
Hello again Tom! Thanks for the additional info. Yes, that is the model number of your Honeywell thermostat.
Your Water Furnace heat pump does indeed have a malfunction output (terminal L or L1 on the furnace's low voltage terminal strip) and if it is wired to the L terminal on your Honeywell thermostat it will light the EM. Heat led when there is a fault detected. I also don't see anywhere in the Water Furnace manual for your particular model that relates to the L terminal output flashing. On later models with a communicating type of thermostat, a flashing trouble led on the thermostat relates to a communication problem or an ECM blower fault.
I will opt-out and perhaps one of our other experts here have seen this condition. Water Furnace does have a tech department that may be able to determine what's going on with your unit. The number is:(###) ###-####
I wish I could have helped more!
Thanks, -Brian

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