I was doing a final charge check on a carrier 38yxa036320 date code 4402, fv4anf003 date code 4402 with a thermidistat today and I noticed something odd.
the OD fan was cycling momentarily only during heat mode. it didn't seem to be going into defrost since ODT was between 50 and 55 f and space temp was in low 60's during this ( no ice on coil but there was light ice accumilation at the defrost klixon during the loss of fan ) . I couldn't successfuly check the charge in heating so I switched over to cooling quickly and everything seemed ok. fan stayed running the whole time in cooling. switched it back over to heat and the same thing again. during lunch I went to totaline and got a new def. board thinking it was a bad relay or something, no luck. OD fan motor was stone cold so the motor wasn't tripping out on thermal. wire wiggle test didn't help either. tried it with and without quietshift ( at that point I was guessing/ trying almost anything ) I didn't have a lot of time to fully diagnose this out since I was there to do a trimout and a final performance check was supposed to be a small portion of my work there. this was a remodel job in which we relocated the equipment and reducted 95% of this system. I have no prior performance history on this system since the HO's just bought this house and had it gutted/ added on to. I know this is going to come up later so I want to have an idea of what to look for. anyone out there had this happen before? does this unit have some sort of motormaster control built into the defr. board? I have never seen a heatpump do this.