RV’s roof air conditioner is not cooling sufficiently. What can I do?

By Dave Solberg
Dear Dave, 
Our rear heat pump, an Airxcel, is not cooling very well. Air going in is 79 degrees; output is 72. Cleaned all filters and also coils on the unit; no help. Also, what should the temperature spread be between air input and output? Ideas? Thanks. —Don, 2017 Holiday Rambler Endeavor 37PE

Dear Don,
First, thanks for the data, as I usually just get “My A/C is not cooling.” The Coleman (part of Airxcel) should be able to “condition” the air 18-20 degrees, so, as you indicated, your A/C is not cooling sufficiently.

How the air conditioner works

The 79-degree interior air is pulled up by the fan and first passes through a filter in the air return grate, which I believe you have cleaned. It then passes through the evaporator coil where the compressed coolant flows through the evaporator coils and flashes, which draws out heat and moisture. The conditioned air is then sent down to the cold air chamber and through the ducted ceiling in your unit. If the evaporator fins are dirty, it will limit the airflow and affect cooling efficiency. You should be able to remove the air return grate and filter to see up inside and visually inspect the coils.

If they are dirty, you can use a shop vac to clean them from the inside. However, it might be best to remove the outside shroud and the evaporator cage and spray on a cleaner that dissolves and doesn’t create much of a mess. You can find one on Amazon here.

Next, check the condenser coil at the back of the unit. It draws outside air through the coils, which cools down the hot coolant returning to the compressor.

Next, check the voltage

If all this is good, check your voltage going to the air conditioner, as low voltage would cause the fan motor to run slower and the compressor to work harder with higher amp draw. If the voltage is at least 115 volts, check the amp draw. A high amp draw would indicate the compressor is getting weak and not compressing the coolant properly and is going bad. There really is no fix to that scenario other than replacement.

One last thing to check would be the air chamber and ductwork. I have found several units that had a baffle come loose inside and the air would circulate in the chamber rather than getting pulled through the evaporator.

Coleman ships the unit without a baffle so it can be used in a direct air application or customized for ceiling ductwork. They also include a generic baffle that the RV manufacturer cuts to size and installs. This baffle is designed to direct the conditioned air to the direction of the ductwork. I have seen some that had just a short piece of duct tape and air was escaping all around the edges, and even some that the baffle was completely unattached. You can fix this by using HVAC tape all around the edges or install a customized baffle called RV Airflow Systems™. It provides a smooth, curved surface for the airflow and increases efficiency. You can find one for your Coleman on Amazon here.

 You might also enjoy this from Dave 

What maintenance does my RV roof air conditioner require?

Dear Dave, 
What is involved with maintaining my RV’s roof air conditioning unit? Thank you! —Randy

Read Dave’s answer.

MORE FROM DAVE ON RV AIR CONDITIONERS

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• Can we test RV roof air conditioner with 110-volt outlet?

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

Read more from Dave here. 

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