Advice on Air/Heating Duct system.

[LeftofSanity]

Hi all.


I have a 1989 Craftsman 28x48 doublewide. When we bought the house, the furnace (gas) was 3 years old. The air unit is self contained, very older looking unit. Looks worn.

I know a guy who does HVAC, and have had some breakdowns with the AC unit over the 5 years I have been here. I have had the compressor replaced twice, the condenser replaced once, the fan motor replaced once and the fan blade replaced once. Basically everything has been replaced, (although the compressors and condenser were re-manufactured/used.) Last time my guy was here he said it was probably time to replace the whole unit.

The cooling wasnt great. After reading here, I may need to check on the crossover. But my unit seemed to run 24x7 to keep it cool. I figured it just kept burning parts out from overuse. I know I have some air leaks to fix, (can feels drafts from some outlets, door jambs etc.)

The furnace doesnt run 24x7 but it does run alot. Was warm while it was running, but 10 mins after it stopped, it was cold.

Would a new AC unit make a big difference?

[DaveyB]

The first clue is that the furnace is only 3 years old, and does heat, but it's cold within 10 minutes of it shutting off. While I'm no HVAC expert, that is a very short time, and would cause the unit to cycle needlessly which increases the running costs and the wear on the unit.

I think you need to look at your insulation first, along with traditional heat exchange points: single thickness windows, gaps around doors, ceiling and floor vent surrounds. You may be able to increase the efficiency of the units, as well as reduce maintenance costs, by decreasing the number of square miles of surrounding countryside you are heating or cooling! (tongue in cheek!)

As you get into summer, try hanging a blanket over each window and door as a curtain and see if the home stays cooler for longer that way. Remove each blanket in turn and feel from the outside for cold air escaping - just wetting your hand will provide a fairly accurate sensor for this. Feel around the edges of the window or door, and feel the temperature of the glass, you will quickly find those points that are below the ambient temperature and so you can begin to decide on a game plan.

Once the leaks are resolved, review your insulation - is it thick enough, and is it doing the job? On a hot day, does the ceiling get hot from heat transfer from the outside? As a comparison, I live in AZ, in a 1996 unit. At over 100 degrees outside, my ceiling is still cool to the touch, and with the AC turned off and the windows closed, the inside temperature is still 20 degrees below the outside temperature at midday. (Obviously it goes up after that, just as a rough guide is all).

From your description, I honestly think your problem lies with maintaining the temperature, not reaching it. Granted, a 22 year old AC unit is not as efficient as a more modern unit, but by increasing the efficiency of the home to maintain a stable temperature for longer, you can increase the efficiency of the unit and drastically reduce your bills and maintenance costs. that way you can begin saving for a more efficient AC unit which will reduce those bills even further.

Hope that is of some help to you!

DaveyB