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Old 11-12-14, 03:11 AM   #6
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Originally Posted by jeff5may View Post
With the evaporator fan not running, while the unit was defrosting, how would the unit know when the hx was frost free? Without another sensor, defrost wouldn't automatically terminate.
I have a temperature sensor attached between the fins of the evaporator close to the intake and one at exhaust pipe end. When HP stops, The temperature start to rise at both. If there is frost at intake, the intake sensor stop to rise at 0C (freezing point) and remains there until all ice melts down. Meanwhile the exhaust sensor's temperature continue to climb to a few degrees higher than ambient temp. As long as the heatpump is cycling (even if outdoor temperature is below freezing), with these two sensors one can clearly identify frost buildup and meltdown.

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