Another teachable moment. HVAC

When I was a rookie I asked: How do you know if its an ac unit or a heat pump and you all said, look inside for a reversing valve.

So now my question is: when you are on the roof and you look inside the unit and see the reversing valve, how do you know if its just a single package heat pump or one with a air handling unit someplace inside the house?

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If it’s a split system there will be refrigerant lines from the outside unit going into the building.

I typically just look at the thermostat to see if it has the third option for auxiliary or emergency heat and confirm by decoding the model number on the outside unit. All the common carriers encode the type an air conditioner or heat pump in their coding system. Google American Standard Model Nomenclature as an example. The third digit is 6 for heat pump and 7 for air conditioner only.


Thanks Randy

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Perhaps the terms are used wrong here, but a package unit is a self-contained HVAC system that doesn’t connect to an interior AHU or separate coil.

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This has always been my methodology as well. Every once in a while I’ll find a HP that is only setup as A/C with the thermostat (so no heat from the HP). All these new Nest, etc. thermostats entice homeowner’s to screw around with the wiring and, of course, if it blows hot and cold they think it’s done right.