Heat pump

Hi all,

Checked a heat pump today. AAON, 8 ton. Model-CA 1003 CA-08-2:OBAOOAO, Serial-200407-CCCF04076 with an air handler Model-H2-C1-2-16-3C2:OOOACAOOOX, Serial-200407-CBEC01183.

The problem as told to me is freezing up during heating mode.

2-27 I first looked at it. 28 degree ambient. 28lbs lo, 42.4 degrees suction temp, 37 degrees comp. SH. 213lbs discharge, 111 degrees dis. temp.

I thought the suction was low and discharge ok. Called AAON and was told that yes the suction was low. Gave them line set length and was told approximately 25 lbs total system charge.

Went back today and recovered 16 lbs R-22. Added 6lbs for a total of 22lbs.

Started up system and kept it on 10 minutes. 43 degrees ambient. 42lbs suction, 74 degrees line temp. Comp SH 55 degrees. Liquid line 265lbs 109 degrees, SC 13 degrees. Discharge line temp, 133 degrees. Press and temp at TXV bulb, 45lbs, 24 degrees, TXV SH 2 degrees.

Sorry I don't have delta T across coils. Supply duct outlets are hot, system will not stay on longer than 5 minutes normally.

I have used the test term. on defrost board to test defrost, works fine. Set on 30 minute defrost timer.

Line size, 1 1/8 suction, 5/8 liquid. 36 linear feet, 11 elbows(LR).

The sales rep. for Aaon told me that the system was supposed to be 2 4 tons instead of the single 8 ton. I am thinking that the system is oversized, does not stay on long enough to defrost.

Any suggestions? Do my pressures look ok for the ambient? I will give a report to the boss tomorrow and see if the rep will spend more money on air flow and sizing.

Thanks
Don in MO