I have a True Gdm-07 that stays below freezing. Do I need to replace the temp control kit?

[ectofix]

Once again, I’ll post this.  I hope it helps:

 

That cooler uses a coil-sensing thermostat.  By that, I mean that the thermostat sensing bulb is actually mounted within the evaporator (cooling) coil instead of being suspended out in the air stream (such as in a walk-in) .

 

A coil-sensing thermostat is designed for cut-out temperatures (to turn the compressor OFF) well below freezing range.  As an example – from 21°F to 18°F (depending on your dial setting).  The designed cut-in temperature (to turn the compressor ON) is around 40°F± 3°.  Again, that’s just an example.

This is a common thermostat configuration for counter-top and prep coolers.  Bear in mind that when temperature within the evaporator coil reaches…say…20°F, the actual air temperature to chill the box would be a much higher – probably around 35°F.

 

Obviously yours isn’t working properly.  Here are several possibilities:

The thermostat is faulty, or… The system’s refrigerant flow is inadequate, either due to a RESTRICTION or a LOW system charge.

 

That latter possibility may not make sense to you, so consider this:

 

If the system is low on charge or if the refrigerant isn’t feeding the evaporator coil as it should, then the coil isn’t getting fed enough refrigerant to supply the coil in its entirety.  As such, it’s likely that the coil section which envelopes the thermostat bulb is no longer performing in the cooling process.

Yet, the section of evaporator coil that IS getting adequate refrigerant – IS cooling.  Consequently, THAT section is doing all the work, chilling the air to sub-freezing temperatures, freezing your product…with that same frigid air passing back through the relatively dormant section of the evaporator coil…to THEN cool the thermostat bulb.  So at this point, the coil-sensing thermostat has been relegated to only sense the 18° AIR temperature.

 

The low refrigerant flow conditions that I’ve described will result in a thermostat satisfying ONLY at a box temperature WELL below what your desired range is, or in some instances, may not satisfy AT ALL.  So the compressor will just keep running…and running…and your lettuce freezes.

At some point when refrigerant flow becomes inadequate to even do THAT, then cooling compartment temperature will become too high.  Again, the compressor would keep running and running, but temperatures will remain higher than the desired range.

 

With that info in mind, you will need to narrow down the problem as to whether its actually a control issue or if it’s a refrigerant system issue.

Looking at my rather DATED service manual, in all True coolers other than wine coolers, the temperature controls cut out well into the sub-freezing range.  So I surmise that they’re all coil sensing type of thermostats.

Maybe someone will correct me if I’m wrong.

[calldave]

So are you saying that I just need to add refrigerant?

[ectofix]

???

 

Your profile leads me to think you’re a technician, although you say you’re not certified.  Well, some of us (me included) learned from OJT.  If you are, then keep learning.  If not, then call one.

 

Nope, I DIDN’T say to add refrigerant.  I was saying that it needs diagnosed first.  It could very well be a faulty thermostat, but you’d need to make that determination after scrutinizing the refrigeration system’s performance.

 

Use your eyes by removing the evaporator shroud to check for localized icing instead of uniformed cooling of the coil – AT the temperature you expect to see.  Localized icing will be either a low charge or indication of a restriction in the cap tube. Use your digital thermometer to sample temperature…with direct probe contact WITHIN the evaporator fins NEAR where the thermostat bulb senses.  Make sure the shroud is back in place when doing that. …And so forth.

 

If those investigations indicate that all is well, then go ahead and replace the thermostat.

 

If NOT and those observation lead you to question the refrigerant system’s functionality, then braze in some saddle valves and use your manifold gauges to observe pressures.  Go from there to determine whether it’s low on charge or restricted.

If you found the condenser coil is (or once was) an abomination of oily-fuzz-packed filth, then the POE oil in the refrigeration system might have ultimately formed a restriction in the cap tube.