[GAHomeowner]

I have an older Nordyne heat pump that has been icing over real bad recently. I checked the defrost board and the defrost cycle will come on when tested but I do not hear it turning on on its own. Upon inspection the coil temperature sensor is not attached to the coil anymore. It is just dangling from its wire down inside the unit. I believe this is my problem. My question is: Where on the coil does this sensor need to be installed and does it matter how close to the original location it is?

 

[user_12345a]

The defrost sensor or thermostat should be on one of the coil u-bends. Location can matter.

See if there are any marks on the coil from having the sensor/stat clipped.


Model number would help to see if it's demand or timed defrost.

 

[GAHomeowner]

Nordyne heat pump model #: FT4BF-036KA
Defrost is demand. Board # is 920338 (I think).
My theory is if it doesn't sense the cold coil, defrost wont turn on unless its really cold out. It tends to freeze when air is in the 30s with wet weather.
I had 2 inches of ice on the outside (and inside) last weekend....



I will check the u-bends on the coil for witness marks from previous location. I hadn't even thought of that. I am not really looking forward to trying to get in there though. Not sure if I can get it through the side and reaching in from the top will be a pain....

 

[user_12345a]

Yah it won't defrost normally like that - being demand, the board checks the temperature difference between the coil and outdoor temp, defrosts if that difference is too great.

With the sensor hanging loose, it can't sense a need to defrost.

Usually, you can't get it from the side and have to remove the fan.

Does the sensor have a clip on it?

 

[GAHomeowner]

I will probably have to wait for this weekend for the repair. No time til then.
I will report back after the repair.



In the meantime I have another question. I had a tech come out and look at this unit recently and told him of my defrost problems and he showed me the defrost worked when the test pins were shorted and said I was OK. He then said he would turn the timing down on the defrost interval. From what Ive learned about my unit you cant actually turn the timing down. So I think he actually changed the terminating temperature to a lower setting as it was on 50 degrees instead of the factory 70 degrees (jumper settings are 50, 60, 70, 80). I will not be using that company again.
My question is how do you determine the correct terminating temperature? Is that just an efficiency thing or does it depend on where you live (humidity, temperature etc...)?

 

[user_12345a]

If the coil still has ice on it when it gets out of defrost mode, the termination temperature needs to be increased.

If your winters are wet/moist, sometimes there may be too much ice on the coil to eliminate everything when the sensor hits 50F. I would go for at least 60, if not 70.

 

[beenthere]

I will probably have to wait for this weekend for the repair. No time til then.
I will report back after the repair.



In the meantime I have another question. I had a tech come out and look at this unit recently and told him of my defrost problems and he showed me the defrost worked when the test pins were shorted and said I was OK. He then said he would turn the timing down on the defrost interval. From what Ive learned about my unit you cant actually turn the timing down. So I think he actually changed the terminating temperature to a lower setting as it was on 50 degrees instead of the factory 70 degrees (jumper settings are 50, 60, 70, 80). I will not be using that company again.
My question is how do you determine the correct terminating temperature? Is that just an efficiency thing or does it depend on where you live (humidity, temperature etc...)?

Yep, determined by where you live. Near a stream, lake or river, will often need a higher termination temp. Dry areas seldom need long defrost times.

If your area has high winter humidity, might need to set to 90.