Norcold 621L Needs Power Bd Reset on every call for cooling

Dougrainer, Thank you for a very informative and explanatory reply. So the initial cool down is, in a sense a "secondary" protective-type measure, similar to primary safety measure of proof of flame?
Except of course that it is protecting the system from further damage.
Interesting. Thanks again.

Paul.../NH

N also called a NO CO code. What that means is this. When the refer starts a cool down, there is a steady progression DOWN in temp-- 65-64-63 and so on. IF the refer does NOT complete an initial cool down within spec, then the refer assumes there is something wrong with the cooling system. This usually means something that can RUIN a cooling unit.
1. Out of level
2. LP flame not to spec/low gas pressure
3. low 120 voltage
4. restricted convection air from the bottom up the top on the back of the coils
5. If condenser fans are installed, they are not working
6. refer door not sealed adequately.
7. A bad cooling unit
When the N happens the refer will allow you 1 chance to turn it OFF wait 10 seconds and then turn it back on. IF THE CONDITIONS THAT TRIPPED THE CODE ARE NOT FIXED, THEN THE 2ND N CODE TRIPS AND IT LOCKS THE REFER OUT AND YOU HAVE TO DO A RESET PROCEDURE.
What this means is simple, there is something wrong with the system(NOT the main board), and you need to find and fix that condition. NOT to continue doing a reset. A BAD Thermister can cause this condition and is a cheap way to take it out of the loop. Since you do not know what is causing this problem and if the thermistor does not fix it, you need to get it to a qualified Technician to find the problem. Doug

Thanks I will pass on the info to my friend and see what they find.

As an aside, my understanding of a thermisor is that the resistance decreases as the temperature of it increases. If the thermistor was bad (either open or shorted), it would tell the unit to either never cool (open) or to always cool (freeze) if shorted.

Our results are somewhere in the middle as once the unit starts, it cools sufficiently until (the thermistor reaches a certain resistance) and then shuts off the cooling. It's on the next RESTART that the unit errors out.

You folks have way more experience at this than I do, but it seems that would tell me that the thermistor is doing it's job. It successfully tells the unit when to stop cooling (we know this because the unit gets warmer inside), and we know it gets warm enough to send a "start cooling" signal, because it tries to start and we get the "n".

One thing I should add is, when the unit is first turned on, I can feel/hear a click in the power board. It is NOT the gas valve, and the igniter does not fire.

It is only after a power board reset, that I hear the same board click as above, but I also hear the gas solenoid open, then I hear the igniter, and the unit starts.

Tnx

rkentzel wrote:
Pull thermistor out find out ohms at thirty two degrees and put it in a glass of water and ice read it with a meter if you have one.

While that is a way of testing a Thermister. A BAD thermistor will still ohm out correctly. Doug

Pull thermistor out find out ohms at thirty two degrees and put it in a glass of water and ice read it with a meter if you have one.

I would try replacing the thermistor first.