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having an issue with a cm 1850
been through 3 boards
two boards blow fuse F5A on the board next to pins 1 and 2 on J5
these pins go to MV1 grilled evaporator defrost solenoid
the issue is the solenoid is constantly open because there is constantly voltage to the solenoid
there is also constant voltage to the heat strip on the grilled evap. cover - this is a completely different harness
the unit obviously thinks it needs to defrost
three boards
three clocks
three rom chips

what is going on?

Have you ever seen this unit working properly?

Do the connections on the input side match the incoming mains voltage?

Meanwhile, am I right in saying that the fuses that blow have been F5 (the 12V supply)?

(I'm trying to relate your symptoms to the circuit diagram I have here).

It looks like there are two solid-state relays in there; have you been able to confirm that they are working OK?

Any other clues? Like, does the compressor run continuously?

No error messages? think
No I have never seen the unit work properly

Yes the voltage is correct and matches incoming mains

the fuse is F5a, which is on the main board itself, not listed in the manual, its a 1a 250v slow blow, not the f5 on the back of the electronics shelf

compressor cycles correctly, so not the crydom relay

also i have swapped the 24v solid state relay on the shelf

i'm at my wit's end

three boards
three diff firmware/ IC rom
three different clocks
same issue

the unit does not blink the time cursor on the display, as if it were in defrost
and the heater strip on the lower tray does not get warm as if it were in defrost,
just the evap coil solenoid MV1 and the evap cover heater strip

Thanks for the attempt let me know if you have any idea where to go

Originally Posted by Chet

No I have never seen the unit work properly

So we have everything to play for, then; the unit have have been "visited by others". smile

If I'm understanding what you're saying correctly, the fault must be outside of the board.

Could there be any chance that those solenoids may be wired incorrectly? "On" when they should be "off"?

And - as the unit may have been played about with - can you confirm that connections from the main board are going where they should be?
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