Bottom zone keeps cooling no matter what temp is set. Top zone stays at room temperature. I'd post a longer explanation but this site keeps rejecting my posts as having a "bad score." Any help would be appreciated.

I have lots of new info. Hopefully someone can help. I've eliminated a lot of possible problems.

1. Here's what the unit looks like:



2. I pulled the circuit board and tested all the caps and diodes. Everything tests OK. While I had all the leads disconnected, I tested both thermistor temperature sensors (it is dual zone) by connecting to the leads on the white and red plugs at the left of the board (see below). I then blew a hair dryer on each sensor for a few seconds and verified that the nominal (room temperature) 2.5 k-ohm reading changed. They are most definitely working.

Here is a picture of the control board:





3. Here is a picture of the compressor area:



I opened all three boxes that you see in this picture. Everything seemed OK. The box that is attached to the compressor on the left has two different, round, enclosed plastic "things" attached, each with one wire attached, using a spade lug. There is then a common wire that goes to both. I saw no way to remove this or test it. Perhaps I should check the voltage being applied to each lead, but I have not yet done that.

4. I set both zones to 55 degrees. Room temp in the garage was a little below 64. After five minutes, this shows the reading:



As you can see, the lower zone had gotten too cold and, if I didn't unplug it, the temp would go to below freezing. The top zone is not cooling at all. This is how I originally reported the problem: no cooling in top zone, and bottom zone will not stop cooling.

5. I used my IR "point-n-shoot" thermometer and pointed it between the grates at the cooling coils. The top zone coils were not cold at all, whereas the bottom zone was very cold.

The next test provided a lot of information, but I can't quite figure out what to do with it.

6. I put some ice blocks in both zones to force the temperature to go below the set points. Once the temp in both zones went below the set points, the compressor turned off, although the fans cycled on and off, which I think is part of the humidity control. Thus, if I can stop the top zone from demanding cold air, the bottom zone will turn off. So, the entire problem may be due to the top zone not being operational.

7. Immediately after test #6, and with both zones off and the compressor not running, I set the top zone (the one that isn't working) down to a low temperature and set the bottom zone to a high temperature so that only the top zone was demanding cooling. I heard what sounded like the compressor turning on, but it sure wasn't making the same noise as before when the bottom zone was cooling.The noise it makes when the bottom zone is cooling is the very familiar refrigerator compressor sound. This seemed different. However, I think it was running.

It is not clear to me how this dual zone works. It sure isn't like a fridge/freezer with a single compressor because I think those usually work with a baffle that shunts air back and forth. This appears to have a separate cooling coil for the top and for the bottom zone. However, I cannot figure how it regulates each one independently.

So here are my conclusions at this point, but I sure would like some help.

1. I think the control board is operating correctly.

2. Both fans are definitely working and both blow into the compartment.

3. Both temperature sensors test OK, and the sensors and board, working together, seem to be trying to do the right thing as the temperature goes above and below the set point.

4. The unit cools the bottom zone, but the top zone cooling coils are getting absolutely no cold. None.

5. The refrigerant valve solenoid only has two wires going to it, so it clearly cannot switch cooling on and off independently for each zone. Therefore, I think it is OK.

I've ruled out a lot of things but, not knowing exactly how this unit manages to control the two zones independently, I can't quite zero in on the fix. However, here are my two best guesses, both of which I don't think can be repaired (by me):

1. If this has a separate Freon charge for each zone, then the top zone may have lost its charge.

or

2. One of those two "things" on the left side of the compressor (switches?) may have malfunctioned.

Any help would be greatly appreciated. Thanks!

P.S. If I can't fix this, perhaps one option would be to mechanically remove most of the top/bottom divider, permanently disable the top zone by wiring a 5K resistor across the sensor plug so it thinks that zone is at 30 degrees. I can then just use it as a single zone unit.

Well, I sure wish I could have gotten some help, but perhaps I can help others with this final post.

I could not figure out what was causing the upper section to not cool (possibly no Freon in that zone). However, since the lower zone that is still working is larger than the broken top zone, I decided to put the unit back in service and simply use it as a single zone cooler.

As you may remember from my first post, the original problem is that the upper zone is not cooling at all, but the bottom zone never stops cooling. But, as you also may remember, I found out that if I fooled the bad upper zone into thinking it was cold (I used a big block of ice), the lower zone worked fine because the upper zone never demanded cooling and therefore didn't keep the compressor running. So, the obvious solution was to put a resistor across the thermistor (thermostat) input on the control board and use a value for that resistor which matches the resistance that would be present when the upper section is cold.

I found a plug in my parts box that matches the plug on the circuit board (I was lucky to have that, and it saved having to solder the resistor in place). I then wired a 3.3 k-ohm resistor across that plug and plugged it into the red (upper thermistor) plug on the board. This made the unit think it was 60 degrees. I then set the upper zone for 64 degrees (the highest setting)

The lower unit worked fine.

But, of course, nothing ever is this easy. When I unplugged the unit to move it, I found out that it quit working. Why? Because after any power outage, this stupid unit has a bad habit of setting itself to a lower temperature, sometimes as low as 45 degrees. So, I put a variable resistor across those leads and changed it until I got a reading of 41 degrees on the digital display. This is three degrees above the minimum setting and several degrees lower than the lowest unwanted temperature setting I've seen after a power failure. The resistance value for this temperature is 5,050 ohms. Obviously there is no such resistor, but I have a calculator I created back in 1975 that will give you the best fit, using either 10% or 5% resistors, using two stock resistors either in series or parallel. I used two in parallel.

The lower portion of the unit is now working as it should, even after power outages.

The one final thing I am going to try to figure out is whether I can turn off the defrost for the upper section. It is a total waste of energy to have the defrost heat applied to that condenser. I wasn't able to determine which connector on the board I need to fiddle with, but I suspect it may be one of the wires in one of the two connectors next to the transformer.