Dear Dave,
We have a Coleman-Mach ducted A/C and heater. When we turn on the heat we get warm air out of the ceiling ducts, but the lower ducts in the wall blow out cold air. The dealer says nothing is wrong. Unless I am mistaken, I would think the warm air should come from all the ducts. The heater does the same thing whether we are running on electric or propane. —Richard, 2022 Cruiser Twilight 2690
Dear Richard,
This is a common misconception by RV owners that have a roof air conditioner that also has a heat strip or heat pump option. A heat strip is just a tape that is mounted inside the housing of the roof unit and, just like the filament of a light bulb, creates resistance and heat. Then the fan portion of the air conditioner can distribute heat.
Heat pump
A heat pump option actually takes outside btu’s, as the air conditioner basically runs backwards and is effective down to about 50 degrees. The air conditioner fan also distributes the heat either through the direct vent or the ducting in the ceiling. The confusion comes when Coleman labels the heat pump option as “Elec Heat” on the thermostat. So, owners think their floor heater will also run on 120-volt electricity.
When the thermostat is on the “Elec Heat” function, the roof air conditioner forces air through the ductwork in the ceiling and distributes heat there. The Coleman roof air conditioner is not connected to the floor heater and subsequent ductwork to the vents. They are two separate systems, with the floor heater running on Liquid Propane (LP) and distributing heat either through corrugated ducting routed through the lower cabinets and sofa to vents, or plenums under the floor with typical residential vents in the floor.
I would believe you had the fan button placed to the “On” mode, which means it typically will run all the time, circulating air. So, you are just feeling ambient air that it pulls in from the cold air return of the heater.
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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All the heat pumps on AC units I’ve had will very effectively heat down to 40F. Even at 35F they produce luke warm air. Having heat pumps has been a mandatory feature in my RVs for over 20 years.