Very Cold Vent Air (56 degrees) during Defrost Even though Heat Strips are On

by Alan
(NC)

I have a new Trane XL-15 3.5 ton heat pump. It works fine except during defrost.

When conditions are: 65 degrees inside; 30 degrees outsid; during 8 minute defrost cycle, vent air is 56 degrees! 10KW Heat strips are on because I monitored at air handler and meter said 40 amps during entire 8 minutes.

Likewise when conditions are 69 inside; 41 outside, vent air is 63 degrees - better but seems cold. Heat strips were on for this too.

Any thoughts?

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Oct 24, 2014
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Added 5KW strip
by: Anonymous

I made original post. Thanks for your comment. I went to 15KW total in heat strips and the temp remains about the same 65 inside when defrost is activated.

Besides activating all 15KW when in defrost, contractor wired an outdoor sensor for 10KW strip to augment heat pump when necessary unless outside temp is below 15 degrees.....then 15KW is activated.

Oct 24, 2014
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Cold Air
by: Ex-HVAC Instructor

Those temps do seem a little cold, however, 10kW strips will produce 34,100 BTUs while the heat pump is producing at least 42,000 BTUs of cooling, maybe more. Probably need to go to 15kW on the strips.

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