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Ask Dave: Why won’t air blow through RV’s AC ceiling ducts?

Dear Dave, 
I had a loose wire in my rear air conditioner and had to remove the duct from the AC downdraft to check the wiring. When I replaced the duct, it now blows directly down and not through the ducting. Do you have a picture of the ducting from the AC to the vent discharge so I can see what was replaced wrong? —David, 2000 Fleetwood Bounder

Dear David,
Typically, Fleetwood used Dometic roof air conditioners on the Bounder model. Those came with a loose plenum that had to be cut to size and positioned in the ducting to divert air flow. Here is a shot of the plenum installed in a Coleman mode we are working on. It should be similar in your Dometic.

How the air conditioner works

The front portion of the air conditioner is the air return that is being drawn in by the fan and is pulled through the evaporator coil. After it goes through the coil and is cooled down 16 degrees from ambient inside temperature, the fan pushes it down the short plenum.

In the case of a ducted air system, the shroud that is screwed to the ceiling is solid with a metal plate so the air hits the surface and is diverted to the sides where the ductwork starts.

 

This photo is the back side of the cold air duct looking at the plenum. Some models have vents on the side of the shroud, as well, to allow some cold air to come out right over the bed.

My guess would be the divider plenum has fallen or pulled away from the edges and is pulling air in through the interior air return, over the evaporator coil, and then right back down through the air return as the plenum is probably blocking the airflow to the ducts. Otherwise, something is blocking your ducts.

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

Read more from Dave here

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