universal nolan condensor fan in reverse on defrost

[stonewallred]

I have seen two universal nolan units, both high temp coolers, that are factory wired to run the condensor fans in reverse while in defrost. Neither one of them have defrost timers and both are cooler condensors, no recievers/accumulators, head controls, nothing. Of course no manufacture tags or model numbers, but I would guessimate about 20 years old. The question I have, nobody around here has been able to answer it, is why the reverse running in a non exsistant defrost mode?

[lurgi]

this feature is called "reverse air defrost", and is found on other cases as well.

it's a bona fide design feature.

[lurgi]

Dammit! never read it right! thought it was about cases.

[icemeister]

There was something familiar about this phenomenon......like I'd seen it in this forum before, so I did a search:

http://hvac-talk.com/vbb/showthread.php?threadid=58922

[stonewallred]

icemeister
thanks, didn't even occur to me to search previous threads.

[kevink1955]

Seems to be some confusion in this thread.

Are we talking about condensor fans (you know, the ones that get hot and are by the compressor) or Evaporator fans (you know the cold ones in the case)

Cannot see any reason to reverse the condensor fans on off cycle defrost, have seen multi fans be pulled backward when cycled by a head pressure switch.

[icemeister]

The original post by stonewallred asked about Universal-Nolin's reversing condenser fan motor setup. Lurgi misread the post and set off the reverse air defrost thing.

The reversing condenser fans were intended to blow crap off the condenser coil during defrost. Kinda lame in my book. :(

[VTP99]

There was something familiar about this phenomenon......like I'd seen it in this forum before, so I did a search:

http://hvac-talk.com/vbb/showthread.php?threadid=58922

icemeister,
I came across one of these yesterday :gah: :grin2:

[ararams]

This is my first post so bear with me. Reversing the condenser motor will get rid of some trash from the condenser, not all but some, keeping the unit cleaner a little longer.Imagine this being done twice a day every day. Universal Nolin was the only company I can think of that had their thinking cap on when they were building units. They wired their condensers that were fitted with copelamatic compressors so that if the high pressure or oil pressure switch opened the pumpdown solenoid will close. Do you know of any manufacture who does that these days. Their condensing with copelaweld compressors had the small domestic refrigerator timer, all you saw from looking down at the electrical compartment was the small part that you can turn to put it in defrost.

[ararams]

Another reason those unit have a timer. The defrost terminal of the timer powered the fan in reverse.

[jpsmith1cm]

True does it, too.

[itsiceman]

The reversing condenser fans were intended to blow crap off the condenser coil during defrost. Kinda lame in my book. :(The ones I see that reverse on the True units are very clean compared to ones that don't.
If they put the thing on every unit my kids will not be going to collage :nopity: :grin2:

[ararams]

I can now say I know the truth about true in 2011. Thanks guys.

[VTP99]

I have not seen this on True units. Is this something new ? What models ?
The Universal Nolen i was repairing showed it on the wiring diagram as an option. This unit is a Hershey's freezer w/2 glass doors and it was the first time i serviced it. I was told by the store owner they replaced the semi twice in the past few years. I noticed no CPR :eek2: When i go back to replace 2 condenser fan motors i will check to see if it has a MOP TXV.

[icemeister]

The True TAC series open multideck cases have reversing condenser fans.

There may be other model which have this feature, but I'm not aware of them.

[BDOLIN]

Running the fans in reverse on air cooled condensers does have some value in pushing dry dirt out. It doesn't replace a good wet cleaning but can be quite useful between them.
I put a unit into "clean" function on a cold day on the roof and the warm air coming off the bottom of the condenser felt pretty good.