I recently moved into a new home (constructed 1989). It has a lot of finished square footage at 3800 sq. ft., including a finished basement. HVAC are Tranes:
-3 ton heat pump with propane auxilliary for the basement and main level (air handler replaced in 2004; outside unit original)
-2 ton heat pump with electric auxilliary for the upstairs (air handler and outside unit both original)
Both systems were recently checked by a HVAC tech who reported that refridgerant levels, pressure differentials and cooling all appear nominal or better. The coil in the upstairs air handler was clogged with buildup, which the tech cleaned out. For the upstairs unit I also had him install a float switch and p-trap in the primary drain as there was just an s-trap there before.
Each system had its own original Trane thermostat which I just replaced with Honeywell RTH7500 units. I followed the instructions carefully and double-checked the wiring. The downstairs unit appears to function normally. But the upstairs air handler (installed in attic) now has an audible hum after installing the tstat, where there was no hum before (or at least I couldn't hear it). It doesn't seem to have affected the unit's operation as the fan kicks on as expected and it cools like it did before. There are 60 and 30 amp breakers on the side of the air handler. Turning off the 60 amp breaker makes the hum stop.
I checked the wiring again and it all looks correct according to the manual. Here's how I did it:
Tstat terminal <-- Unit wires
C <-- B
G <-- G
Y <-- Y
O/B <-- O
Rc <-- jumped to R
R <-- R
Aux <-- W
E <-- X2
L <-- not used
<-- T (tstat has no receptacle for thermistor wire)
The downstairs unit is wired the same way. The tstat is used to differentiate what sort of system and auxilliary you have, which I did and double-checked. I set up the upstairs unit for the following:
System type: heat pump
Heat pump changeover valve: cooling (O wire connected to O/B)
Emergency heat cycle: electric furnace
Any idea what could be causing the hum?
Second question: The house is generally quite humid. Since the tech told me everything checks out regarding both units' operation, could the humidity simply be a result of this being an older house? I can think of several contributing factors:
-the windows are original (wood)
-some of the exterior doors don't seal very well
-the blown insulation in the attic is covering up the soffet vents (I need to rake the stuff back to uncover them)
-I live in a humid climate (northern Virginia)
The house I came from is in the same general area but was a recent construction. I never measured the indoor humidity there but it was comfortably dry. In the house I'm in now it's upwards of 70-75% according to the humidistat on the little dehumidifier I bought from the hardware store.
Are there any simple steps I can take to improving my system's dehumidification, or do I just need to deal with it until I can afford to replace windows and doors? Should I consider retrofitting dehumidifiers to the air handlers themselves (big expense)?
Thanks for the space!