~~~AAA~~~ wrote:
The old stat was 22 years old and each and every time that the heat
would automatically go on, the blue auxiliary light would light up.
Should the auxiliary heat always be on during calls for heat? Also,
the room temperature and set temperature were not in sink, being off
about 5 degrees.

Aux heat should only be on when the heat pump can't keep the temperature
at the set point. If it was really cold outside (say below 20 degrees
F) it might be normal for aux heat to be on virtually all the time.
OTOH the temperature error is certainly a good reason to change the
'stat. Your new 'stat is a very good piece of equipment.

AKA is the same as emergency heat? I thought they were separate
issues. My new TH8320U has Heat on, Aux Heat on, and then a separate
Emergency heat indicator. Am I not understanding this correctly?

On an all-electric (no gas, no oil....) system there is only one source
of supplemental (aux or emerg) heat - resistive heat strips.
"Auxiliary" heat means the strips are on in addition to the heat pump,
"Emergency" heat means the strips are on but the heat pump is off.
Uusally the selection of aux vs. emerg mode is made at the thermostat.
Emergency heat will also be selected by the heat pump when it is in
defrost mode.

If aux heat is inefficient above 20 degrees should I simply set the
aux heat lockout at 20 degrees and above so that only the compressor
would operate?

Not necessarily. Since your systems is "all electric" in most US
climates you are better off letting the heat pump run regardless of the
outdoor temperature. You will almost alwasy get cheaper BTU's from the
heat pump than from resistive heating. At lower temperatures the Aux
heat will be on most, if not all of the time.

http://oee.nrcan.gc.ca/publications/...dequipment.cfm

Maybe an intermittently stuck fan relay? If so I guess I should get a
professional to look at this and fix if necessary.

That would be my recommendation.

Re the heat pump, I do get the Heat On indicator and warm air comes
into the room, and sometimes it will switch to saying Aux Heat On,
also with warm air. Since Heat On brings heated air, does that mean
that the compressor is in fact working?

That would be the logical conclusion. If you have access to the outdoor
condensor you can check to see if the compressor is running; you should
also get colder-than-ambient air out of the exhaust side of the
condenser.

If the room temp is indicated at 70 and the set temp is 72 I will see
the Heat On indication and warm air. If I move the set temp higher
even a few degrees, the Aux Heat On indicates. Normal?

Perfectly normal. The thermostat thinks that the heat pump can't keep
up with the set point demand, so it turns on the heat strips (aux mode).
Most thermostats turn on aux heat when there is a 2 degree (F)
difference between the current temperature and the set point
temperature.

Last Q: Is it better or not to utilize the temp lockouts for
compressor and aux since I added the outside temp accessory to this
new stat?

I wouldn't use the lockouts unless you are sure you know the temperature
at which your heat pump costs more to run than it produces in heat
energy - which is going to be well below 20 degrees, perhaps as low as
zero or below. You might be able to divine this information from the
manufacturer of the system - assuming that the system was 'matched'
(outdoor condensor, inside coil and expansion valve) when it was
installed, or from a very experienced service tech in your area. Here
in my part of Florida it never gets cold enough to lock out the heat
pump.