I had a new Rheem system put in last May '08:
Heat Pump: RPNL030JAZ
Thermostat: (-)HC-TST411MDMS (The modulating model)
My understanding is that in heat mode the heat pump should not come on once the outside temp goes below some programmed value. I think I remember the installers say that that value was 35 or 38 degrees. That has worked fine but once the outside temperature warms back up the heat pump is not coming back on.
I called my installers and they came out and looked things over. The guy said the furnace filter was clogged and that was triggering a pressure switch to keep the heat pump off. So I made sure the filter was clean all the time but the problem returned. I could reset the system by turning off the breakers for a few minutes when it happened but it was happening every time and the filter was clean.
So I had them come out again and this time another guy said he "changed the path of 24v common from through defrost board to thermostat." Well, the heat pump is working now but it is coming on well below 35 degrees and I noticed that ice is building up inside the unit.
I worried that with the heat pump not starting and stopping at the proper temperature I'm not getting optimal efficiency, and I'm worried that the ice will damage the unit. I'm about to lose confidence in my installers & I'd like some other opinions on what should be done.