Had a NEW electric furnace and heat pump installed a month ago. Installer suggested I should increase the size of my return air ducts. The house is a 1950’s bungalow, 1000 sq. ft. plus a basement.

I removed the grates off the returns and measured the openings going to the ducts. There were only 3 return openings measuring a combined total of 108 sq. in.

Everything worked fine until a couple of days ago. The A/C stopped cooling and when I looked the line going into the coil was covered in thick frost. Not the insulated line. The non-insulated one. I called the service people and they wanted to know if I had increased the return duct size. I had not. This they claim could be causing the problem.

Worked all day Sat. installing another return grate and ducting to add another 52 sq. in. bringing the total to 160 sq. in. Still getting frost to the extent I have to shut the A/C off every few hours.

The duct size going into the bottom of the furnace is 210 sq. in. Do I have to further increase my return ducts by another 50 sq. in to match this or am I completely off base. I am no HVAC pro by a long shot.

To give the A/C additional return air I opened the cleaning port in the return duct and left the filter door off. Still getting frost.

I think I have more than a return air problem. Any comments or suggestions welcome. Should I increase the return ducts some more or is it likely I have another problem. The service guy is coming back this week but I don’t think I can accept if he claims this is all due to duct sizing.

Thanks in advance.