View Full Version : Defrost issue

Upper crust
12-06-2016, 10:14 PM
Evening all, just wonder if anyone can help as my fridge engineer has fallen off the planet !!
Anyway, simply put, I'm running a foster freezer, with an mcdu11/2 controller (oldies but goodies lol) so, last week I dropped the panel housing the controller and pulled out some of the wires. In the process, it pulled one of the lives and shorted, blowing the plug fuse!
After rewiring it (correctly) and restarting, all works fine, temperature, defrost etc. Two days later after putting the food back in, freezer goes into defrost (at least the controller thinks it has, correct led showing and def on the screen) but....it hasn't actually gone into defrost so continues to run, icing up evaporator and pipes, losing temperature as to be expected. Won't go into defrost manually after resetting etc. So , I allowed it to fully defrostand restart it. Works fine again for two days and bang, same again!so, unless it's coincidental, I fear maybe an intermittent fault caused to the controller when wires pulled and shorted (despite appearing fine and working afterwards) am I correct in thinking that basically the reverse gas defrost system is all mechanical and is only switched on and off by the controller? In all of your opinions is it likely to be the controller or have I missed the obvious? It's thrown me with the working fine for two/three days , including the defrost system. Thanks in advance

12-06-2016, 11:17 PM
Either be electric defrost where compressor would be turned off and heaters energised or hot gas defrost where compressor will run and hot gas solenoid valve energised.
Is working fine for 2-3 days just the time it takes to ice up?

If it was working fine before then chances are the wiring didn't go back correctly. Defrost output from controller goes to heaters or hot gas valve depending on type. On the face of it missed the obvious but coincidence has a chance of showing up when least expected. Or is that just me. :-)


Edit: To help testing, press bottom 2 buttons together for a few seconds to force a manual defrost. Might not work if interior is already too warm though.

12-06-2016, 11:25 PM
What does the temperature drop to when it's been on a few hours after the manual defrost? Seems like the LAE relay is welded shut or you have crossed a wire.