The title was just marketing. I'm interested in differences.

Up to now, I have mostly been checking heat pump
performances by putting them in cooling mode, verifying
that they cool well, before moving them to heat mode.

For folks that actually see a lot of heat pumps, are there
some things about running them in A/C mode that are
different than your typical A/C-only unit?

#1 What is a fairly typical return air grill versus
supply register temp difference in HEAT mode?
In A/C mode, with newer (better airlfow) installations,
14 degrees is typically what I see.

#2 Does gauge behavior vary with heat pumps?
In cooling, I was seeing my suction side go WAY down before
creeping back to normal. I was thinking maybe
the check valves take a bit of time to close off
or something, or should gauge behavior be identical?
And fluttering, my suction gauge fluttered about five-plus psi
for about five seconds before dropping. I have never seen
that in A/C-only units.

#3 In cooler, maybe 45 degree weather, does the
TXV for heating almost immediately frost or could that
point to a problem?

#4 Not quite on topic, but do the test terminals on
defrost boards have some DEFINITE way of working?
I rarely find manuals with units, and am always leery
(more scared) about jumpering test terminals. Do you
always jump test to common or force defrost to common
or force defrost to test? Are test terminals typically
tolerant of being jumpered to ground or 24V, regardless
of what they are SUPPOSED to be jumpered to?

#5 From the very vague instructional articles I've read,
check valves seem to be mysteriously built into TXV's
and the like. But I'm thinking they are actually very separate
piping coming off both ends of the TXV. Am I wrong or
am I right?

Any other bits of enlightenment are welcome. When I
am actually working with a troubled unit, I tend to forget
every bit of basic theory about them. Stuff I read on here
tends to stick better.

Really, I want generalities, if they can be relied upon.
If there are none, then that would be useful too. I mean,
should I be looking into truck driving if I meet up with too
many heat pumps? The bad ones are kicking my head.