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-   -   Defrost mode on heat pump. (http://www.diychatroom.com/f17/defrost-mode-heat-pump-121013/)

roku 10-23-2011 11:20 AM

Defrost mode on heat pump.
 
My heat pump is set to defrost cycle at 90 minute intervals. I recently noticed that the defrost came on when the temperature was 59. This does not seem right at that temperature. At what temperature should the system be in for a call for defrost mode. What would cause this?

hvactech126 10-23-2011 11:28 AM

do to your control being a timed defrost control board it will defrost at 90 min run time no matter what the outdoor temp is.

roku 10-23-2011 11:38 AM

If this is the case. I'd like to manually control when the auxiliary heat strips come on in defrost mode. It seems ridiculous to have them come at say 50 or even 40. I know I can disconnect the wire that engages the heat strips while in defrost mode. Is there a switch I can use so I would not have to physically disconnect said wire?

hvactech126 10-23-2011 11:54 AM

yes, a switch could be used at the air handler that would break the circuit for the strips from the heat pump, but while the unit is in defrost it will be putting cold air in the home then.

roku 10-23-2011 12:05 PM

I fully understand that. But I am thinking more on cost savings at those temps as compared to dealing with cool air during the defrost mode. I can tinker with it to see what temp I can withstand without the auxiliary heat strips coming on. What type of switch can I use to make this happen?

hvactech126 10-23-2011 12:17 PM

honestly just about any switch will work. spst.... a light switch would work or something from a auto parts store would work as well. It's not going to pull more than 1 amp through the switch. All you are doing is opening and closing a circuit.

roku 10-23-2011 12:23 PM

Would I not need a switch specific for that of a thermostat wire? Not sure but I think it is 24vac for the wire.

hvactech126 10-23-2011 12:24 PM

yes, 24vac.... so anything rated for that or higher voltage will work

roku 10-23-2011 12:28 PM

Do they sell a 24vac switch in auto parts stores? Having trouble finding one online.

hvactech126 10-23-2011 12:38 PM

not specifically for 24VAC... if you are not sure then go to the hardware store and buy a 2 X 4 metal box, light switch, and cover.

Marty S. 10-23-2011 12:52 PM

There should be a defrost sensor on your heat pump that starts the timer when the line temp is 28-30 degrees. When the line temp stays above that then the timer is not activated but the board will initiate a defrost after 6 hours of run time no matter what the temp for oil return to the compressor. Low on charge, dirty coils,a weak capacitor or a dragging motor can all cause frost to form too soon resulting in excessive defrost cycles. If there wasn't frost then it could have just been the oil return cycle time.

hvactech126 10-23-2011 12:58 PM

Quote:

Originally Posted by Marty S. (Post 754849)
There should be a defrost sensor on your heat pump that starts the timer when the line temp is 28-30 degrees. When the line temp stays above that then the timer is not activated but the board will initiate a defrost after 6 hours of run time no matter what the temp for oil return to the compressor. Low on charge, dirty coils,a weak capacitor or a dragging motor can all cause frost to form too soon resulting in excessive defrost cycles. If there wasn't frost then it could have just been the oil return cycle time.


they do not all have that sensor

roku 10-23-2011 01:01 PM

So are you saying that I can use a basic single pole switch for this? If so, is this how to wire it? Wire from airhandler hooked to top of switch and wire to heat pump condenser hooked up at the bottom of switch.

hvactech126 10-23-2011 01:15 PM

yes, basic single pole switch. From W2 of defrost control to switch. From switch to heat element terminal in air handler.

roku 10-23-2011 02:05 PM

"From W2 of defrost control to switch" Is this wired to the top of switch?

"From switch to heat element terminal in air handler" Is this wired to the bottom of switch?

Would the wire from the defrost control board be considered the power source?


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