Most units (not all) have a board that will only allow so long of a defrost
whether it's done or not. Not saying that it ISN'T getting stuck in defrost,
but not likely. Could be the reversing valve not "opening back up" all the
way when coming out of defrost. Have you looked at the outdoor unit when
it's blowing cold air" If it is getting "stuck" in defrost, the fan won't be
running.

BTW, what kind of outdoor temps are you talking about when it does this?

wrote in message
.. .
In article , Bob wrote:
The supply temperature of an air to air heat pump will feel cold because
it's lower than your body temperature. He has no back up heat, so the air
never feels warm. In a typical tract home where the builder hired the low
bid HVAC contractor, the duct work may be too small, so the velocity of
air
coming out feels even colder because of a wind chill effect on the body.



OP here.

Thanks.

However, in this case, it will blow as cold as when in AC mode for
very extended periods ( much longer than defrost cycles ).

So cold for so long that the whole house gets gradually colder instead
of gradually warmer.

I'm really curious if the defrost circuit is bad or if the
thermostat is insane.

When the heat pump desides to start blowing cold, the voltage
at the reversing valve lead at the thermostat goes from
26.6V to 0.0V.

Is this voltage change due to a "command" from the defrost control
circuit?

Can the defrost control circuit even drive that voltage level?

If not, It would seem that the cold is due to the thermostat
loosing its mind.


Again, thanks for any help.