reverse cycle ac units that keep on running

Not that I know of, same problem here. Maybe we can learn something new, I just assumed that was the way is had to be... I just turn off the units when I get annoyed by the air blowing...silly me maybe?
Greg

hey guys

My 1998 vintage SMX controllers reduce fan speed as the temp comes down (are you cooling or heating). Never completely turns off once it reaches the lowest speed, though, to keep the air circulating past the remote thermostat for a proper temp readings

AC units

Yes most of the fan units can be adjusted down so they blow less. I had mine done last year. According to my AC rep he said the fans must always blow to prevent the units from icing so they never turn off.

Makes sense, I will have to pay attention to the fan force to see if it cycle down while the compressor is not running.
Cheers,
Greg

Yes, if you get the owners manual for your control you can control the percentage of speed the lowest setting runs at. But they do need to constantly run as said above.

I have seen the fan wired into the compressor so that the fan turns off with the compressor.
This is good when using the reverse air for heat so that the fan does not blow cool, or non-heated air, when the compressor turns off.

I personally, never got around to doing this and when using the reverse cycle heat it can be annoying that the fan is always blowing.

I've encountered this on a few boats, but on most I've never noticed. Something seems wrong with this logic however. Why would the unit be icing if once the compressor turns off?

I have the SMX II which should be the same. It allows you to program fan behavior and speed. The fan can be off or run slow when the compressor is off.

In our instalation, the thermostats sit right next to the condenser coils. We find that if we don't keep the fans running slightly, the system has a hard time judging the actual room temp. Versus the temp of the big metal object it is attached to. Come to think of it, this might be a good spring project for me... Move the thermostats!

My unit allows me to switch the fan from continuous to intermittent. Don't have the book w/ me, but check the web- site. I use the intermittent with heat, and continuous with AC.

While switching to intermittent fan occasionally works without relocating the temp sensor, you will usually end up with wider temperature swings between on/off cycles. With the sensor in front of the coils when the fan shuts down the coils residual will fool it into thinking the room is still below setpoint when it isn't. Until the coils reach room temp, which can be a while if the return ducting is long, it will not restart.

We always move the sensors somewhere near the center of the room or where people will be the most often. Try and keep it away from the airflow coming out of a discharge and not in a cabinet with heat generating equipment like fridges or stereo and make sure it's not exposed to direct sunlight coming in through a window. I usually tuck them underneath a countertop overhang when possible.

Once the compressor shuts down, the coils are still very cold and can freeze because the airflow would stop instantly and the fan isn't blowing warm air over them to get the excess residual low temperature out of the coils once the unit shuts off. Kind of like when you use hot water at a faucet, and then turn it back on 10 minutes later, it's still pretty hot at the tap because it takes a looooooong time for the pipe to cool off just relying on surface to air heat exchange.

We're talking about heating here. See page 12 for programming fan operation.
I like this function for heating, but for cooling it is nice (the icing issue aside, which is a real issue) to have the fan operating regardless.

http://www.dometic.com/FileOrganize...ir Conditioning/L-2218-Smx2smxiroperation.pdf

I was answering Nycap's question regarding the unit freezing in his post above......I realize it is heating. I have seen the compressor unit form a block of ice on it, while heating,....but that's not a fan related issue but a freon issue.

Jimmy

Have a good season!