Lennox defrost problems

[Daikin=Overated]

Happy New Year to you all.

I'm working on an old Lennox Refac series
LFB 8E. It's an R-22 heat pump. I can't find any manuals on the Lennox site to support this system which isn't helping.

In the recent cold spells considerable ice build up on the condensor coil has been causing the system to fail. Fresh air is ducted in and then out the other side of the condensor coil.

The condensor fan was off when I first got to site, the compressor running so it was trying to defrost I believed. At the time I checked all the basics, gas, protective devices and found that the compressor o/l had tripped. I reset this and watched the system fire away happily.

It's done the same thing again since my last visit.

I recall to the system having a low ambient presure switch labelled D2 on the control side of things, I don't remember seeing a stat nor a thermistor on the coil either so I'm wondering what's sensing the frost on the coil and in turn engaging the defrost cycle?

I'm going back there to investigate the four way valve operation, and see what else is out but of course by then the system would have defrosted.

Has anyone encountered similar, or have any experience with this system?

Many thanks.

J.

[marc5180]

Are you still having trouble with that lennox unit?:D

I ordered a TXV for circuit 2, 10 weeks ago (it was on a 12 week delivery from danfoss) so i'm expecting to be going back there to fit it any day. Not looking forward to it.

Anyway when we were having problems with the defrost side this is something i was sent. I know that our models are different but maybe this well help you;

The defrost timer is energized by the defrost thermostat located near the drier on the liquid line leaving the outdoor coil. When the defrost thermostat is closed, it will start the timer. The defrost timer will go into defrost after the specified amount of time (as determined by the timer settings on the circuit board). Once the defrost is initiated, it is terminated by the defrost thermostat, but the amount of time it can stay in defrost is limited by the timer. I believe the timer will terminate the defrost after 10 minutes even if the defrost thermostat is still closed.

[Daikin=Overated]

Marc.

Cheers for that!

I'm due back there tomorrow, and was thinking down the same line actually. I hadn't found any defrost stat, but do recall seeing a drier behind the controls area. I will further investigate, and let you know how I get on. Much appreciated.

Regards.

J.

[Daikin=Overated]

Just a quick update.
Took a load of readings away with me from site today for calculating Subcool/Superheat to confirm it was a little low on gas. Suspect blocked filter/drier too.

Lennox tech support where shockingly bad today (didn't even return my call) so i'm none the wiser on the control side and defrost functions though I did remove the PC board to inpsect relays, tracks and for any dry joints. All ok. Also found stat problems so think I have this one pretty much sussed.

Here's to getting the parts out of them!

Thanks chaps.

J.

[marc5180]

Thanks for letting us know. Keep the thread updated if you do figure it out, many people will benefit. Myself included:D