View Full Version : Long defrost cycle during cold windy conditions
01-30-2007, 02:40 PM
I have a lennox heatpump/electric blower system and have noticed a couple of times this winter that if the outside temps drop to about 20 and its very windy ouside that the unit will stay in defrost mode sometimes for 20-30 minutes even though there is no ice on the unit. It did this again last night. It got down to about 17degrees but the windchill was close to 0. I thought maybe the defrost contact was stuck but noticed if it is not windy that the defrost cycle is the normal 1-3 minutes. Has anyone ever seen this problem before? I mentioned it to our service tech and he said the wind was probably confusing the sensors.
01-30-2007, 03:13 PM
A couple of my guys said the same thing, especially when it gets that cold with the wind chill.
01-30-2007, 03:16 PM
You might check to see the sensor is making good contact with the end bend.
01-30-2007, 06:13 PM
On a cold windy night, could take some time to get a big coil up to 70°. But every board I've heard of times out after 10-12 minutes. So if you are really running longer than that, you may have a bad board.
01-30-2007, 07:40 PM
You may have issue with defrost control board. I thought that wind chill doesn't affect a thermostat's ability to read temps. but I could be wrong.
The board should time itself out well before 20-30 minutes and end the defrost regardless of the stat's open or closed state.
02-02-2007, 02:51 PM
If there's no wind, then perhaps radiant heat from the sun could create a "blanket" of warmer air around the unit and its thermostats. Otherwise, wind has nothing to do with temperature.
In some cases, a heat pump will have an "on demand" defrost cycle, but I believe most Lennox systems will have a simple timer that calls for a defrost cycle. On older-ish models, the frequency of the cycles is adjustable by a jumper on the defrost board (30, 60, or 90 minutes) However, regardless of the frequency, the defrost cycle lasts 12-15 minutes. If your's only lasts a few minutes, it must be an "on-demand" type and the defrost thermostat is poorly located or wonky.
My 2 cents.
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