Selecting 30, 60, 90 defrost timer.

[georgelass]

Is the recommended setting in the install manual or what?
I'm not understanding why there should be options since
the temp sensor doesn't have an option (and there is no
humidity sensor).

I'm not having any particular issues at work. I'm merely
reading up on heat pumps and I thought maybe an explanation
of the need for these various timer options would provide
insight into an icing problem were I to encounter one.

Thank you. (Expect another heat pump question in the
next few days. I'm still reading.)

[Rob_in_WV]

Units located in shady areas will require more frequent defrost intervals. By setting the board timer from 90 to 60 it means that after defrost stat closes it won't have to run for an extended amount of time before a defrost.

[SgtBone]

I suppose it would depend on where you live. Units in Fl may only need 90 while units in the north need 30 min intervals.

[Snapperhead]

On my Own unit , I can set it 60 minutes during mild winters , but if it snows alot , or freezing rain , I will set to 30 min , otherwise it will frost up pretty good if I dont

[georgelass]

So if you set it for 30 minutes in mild winters, couldn't we assume that the
thing wouldn't go into defrost often, and were it to go into defrost, it would
be brief? What would the downside be of setting it to 30 minutes in mild
winters?

[Kon99lbi]

To best answer this question, I think its better to understand the defrost cycle on heat pumps. In a timed-temperature defrost, both timed (defrost timer motor) and temperature (temperature sensor) conditions must be met in order to initiate defrost. All the temp sensor does is close when the outdoor coil has reached a temperature below freezing. In environments with erratic temperature swings, the coil temp could vary in and out of the sensors threshold. Defrost cycle on heat pumps is inefficient because it initiates cooling and tempers the supply air by energizing the auxiliary heat. This is why another condition must be met in order to ensure the defrost cycle is needed. The timer motor does a brief trial defrost every 30, 60, or 90 minutes. In colder areas of the country, your unit might require more frequent defrost cycles, thus the timed portion of defrost is adjustable to occur more often and visa versa in warmer parts of the country. Hope this helps

[Kevin O'Neill]

It depends on how humid your climate is. In dry climates, you will not need defrost very often. In humid climates, the moisture in the air condenses on the outdoor coil during heating mode. If the outdoor coil temperature is below 32 degrees, it turns to frost. In those humid climates, there is more moisture in the air, so defrost will be needed more often.

[Snapperhead]

So if you set it for 30 minutes in mild winters, couldn't we assume that the
thing wouldn't go into defrost often, and were it to go into defrost, it would
be brief? What would the downside be of setting it to 30 minutes in mild
winters?

if you have it set at 30 , it will defrost every 30 min ( as long as its cold enough )

How long it stays in defrost is determined by the sensor on the coil. When it senses the coil is clear it will turn off defrost.

[air1]

if you have it set at 30 , it will defrost every 30 min ( as long as its cold enough )

How long it stays in defrost is determined by the sensor on the coil. When it senses the coil is clear it will turn off defrost.

It will only defrost if the defrost thermostat is closed.
90 minute setting should be used whenever possible to avoid unnecessary defrost cycles. You should only increase defrost frequency if you are experiencing problems with ice build up on the coil. After a while you should get a sense of what the optimal setting is for your area or for special circumstances like equipment located in cold damp environments.

[Kevin Weaver]

I have always chosen 60, in central Indiana. And that's 60 RUN minutes.

I have always said that if you can get a heat pump to defrost, you won't get called back, even if its not running exactly perfect.

[fliks]

Here in central texas I use 90.

[ADillon]

The correct setting will vary from application to application, area to area, and year to year (or even month to month depending on the outdoor conditions) It is usually set as high as possible and then reduced if defrost issues are encountered. Remember that a time temp board initiates on BOTH time and TEMP and so you wouldn't adjust the 'sensor' which is simply a bi-metal switch. Getting these set right has always been a little bit touchy feely but the longer the better as defrost cycles = electric heat = high bills.

[Kevin Weaver]

Thats the reason manufactures have went with DEMAND DEFROST. now the question is, what temperature do you select for termination?

I choose 80 degrees.