How to switch my central unit thermostat from cool to heat?

Question

Okay, we installed a thermostat last winter & it heated the house fine. When the summer came, the AC would not blow cold air, it just blew hot air. I called my friends husband & he said the thermostat only works for heat or AC, either one at a time & that he had to "switch" it from heat to AC. After he came over & spend 5 mins. "switching" it over the AC worked perfectly but the heat wouldn't blow hot air, just cool air.. which was fine b/c it was summer time. Now we are back in the winter weather & I dont know how to "switch" from AC to heat. So my friend isn't married to the guy that came over & "fixed" it last time & Im not sure what to do!?! It is a Honeywell Non-programmable thermostat RTH5100B & I guess it only supports either heat or air, one at a time. I did notice that the guy that "fixed" it last time took the face off the thermostat. Does anyone know how I might can try to switch this from cool air to heat? Its going to be a very cold night tonight & it would be nice to be able to be warm in the morning! Thx!!

Answer 1

I answered this on your duplicate question.

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Answer 2

Set System Setting
Press the System button to select Heat, Off or Cool:
Heat—Thermostat controls the heating system.
Off—Both the heating and cooling systems are off.
Cool—Thermostat controls the cooling system.

Source(s):

http://www.instructionsmanuals.com/u2/pdf/termostato/Honeywell-RTH5100B-en.pdf

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