Original message
| WaltA
 |  "Heat Pumps: Aux Heat vs. Emgergency Heat"
, posted Mon 15 Dec 17:53  
I am trying to change my old mercury-tube thermostat to a nice new electronic thermostat.
I have a York heat pump, which has only one backup heat source, and that one backup heat source is used for both aux heat and for emergency heat.
I got the installation manuals for both thermostats, and matched up each function, and planned to move each wire from the same function screw terminal on the old thermostat, to the same function screw terminal on the new thermostat.
Well, "cool" mode works and "heat" mode works, but "em heat" mode doesn't work. And that brings me to here asking for help.
Amongst other screw terminals, my old thermostat has a screw terminal for "aux heat" and a screw terminal for "em heat". And my new thermostat has a screw terminal for "aux heat" and a screw terminal for "em heat".
Well, when "em heat" didn't work, I got out my old volt/ohm meter, and check a bit on how the new and the old thermostats really work.
What I found is that on my old thermostat, the "aux heat" screw terminal would go 'on' and 'off', as there was need for either aux heat when in "heat" mode, or there was a need for emergency heat when in "em heat" mode. The "em heat" screw terminal would go 'on' and stay 'on' constantly whenever I am "em heat" mode, and be 'off' in all other modes.
With the new thermostat, the "aux heat" screw terminal would go 'on' and 'off' ONLY when there is a need for aux heat when in "heat" mode. The "em heat" screw terminal would go 'on' and 'off' ONLY when there is a need for emergency heat when in "em heat" mode.
Sorry for being a bit long winded here. It seems that for my old thermostat, the "em heat" screw terminal is really for nothing more than turning the "em heat" LED 'on' and 'off' (and possibly error indication?). The "aux heat" screw terminal is really for the backup heat source, and will exclusively turn it 'on' and 'off' be it for aux heat or for em heat.
So, my question is, should I jumper the "aux heat" screw terminal to the "em heat" screw terminal on my new thermostat, so the either could turn on my backup heat??? Basically, trying to get it to work like on my old thermostat.
I guess I could possibly connect up the wire which use to go to the "em heat" screw terminal on my old thermostat, to the new thermostat's "L" screw terminal. From the installation manual, that looks more like the right place for turning on the LED 'on' and 'off'.
Any thoughts or comments???
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Replies:
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| xenos
Webmaster 
| "Re(1):Heat Pumps: Aux Heat vs. Emgergency Hea" , posted Mon 15 Dec 18:33
On a standard heat pump thermostat you need to jump E ( emergency heat) to W2 ( aux heat) on the thermostat.
Xenos.
The best way to escape a problem is to solve it.
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