I recently got a new Carrier HVAC system. Mine is a oil fired forced hot air with A/C for the first floor and a heat pump for the second floor. The first floor blower runs continuously on low speed. When heating or air conditioning is called for, the blower ramps up to full speed. The heatpump upstairs does not work the same way. For it, the fan is either on or it’s off. I recently had a guy out (not the original installer) to see if the upstairs heat pump could be made to function the way the downstairs unit does. He said no, that the downstairs unit was not working properly. The installer says it’s correct. Who’s right? I like having the blower on low continuously; it really evens out the heat and A/C. Is there a way to make the heat pump work similarly?
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Well, the first requirement would be that the upstairs unit be equipped with a dual-speed (or multi-speed) fan, and that the speeds be electrically controllable by some means other than dinking with the innards of an electronic gizmo. Given that, it's a simple matter of designing the right arrangement of control relays.
That may be built into the design of the downstairs unit (and not on the upstairs). Using a variable speed fan has been getting more residential use lately. But, it is not universal. I'm guessing that the fan controller is unique to the unit, and not an add-on part. Which would explain both the installer and the tech's opinions.
Ok, googled, it looks like the variable speed fan is only on the a/c & furnace combo units, which would explain it.
You could check out the hvac mechanic's forum, but they can be right rude to folks not in the "biz".
Probably the downstairs fan runs continuously because you have "Fan" set to "On" on the thermostat.