Thanks for the advice to look at the simple stuff; I would like an easy
answer to this. The indoor coil has a fccv, not a txv, but the heat
pump does have a txv, don't all heat pumps have one? I did not check
any pressures in heating mode.
The indoor coil is clean as new; the outdoor coil looks good but could
stand to be washed. I did not think much of it because of the
extremely low high side pressure in cooling. Also, the only returns in
the house are high air returns.
Bubba, The details of how I determined airflow were; I used a
"magnehelic" to measure static pressure from below the coil to a
reference point at the filter. The needle actually bounced between 0.4
to 0.5 depending on how the sensing ends were placed in the air stream.
I am aware of the difference in using the different motor speeds taps
in heating and cooling and moved the taps to see the effect on my
readings. The Trane "service facts" sheet has a nice table listing
the airflow at the different motor speeds at a given static pressure.
To double check I measured the temperature rise in heating with the
The Output BTU is specified at 63000 Btu/hr, I did not measure this,
and my temp rise was 47 deg (measured return air boot to plenum delta
T) I then used CFM=BTU/hr divided by temp rise times 1.085.
63000/(47x1.085)= 1235 CFM
The unit is rated at 2.5 ton (the 30 in the part number TWR030C)
What can cause a low High side pressure and a high low side pressure in
cooling mode, in a heat pump, and cause very low btu/hr output in
What things would check, in what order, and how?