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Old 08-09-15, 08:51 AM   #1
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Default Another heat pump food dryer

Decided to take a crack at this food drying thing since the garden is getting ripe... Took an old fridge and disconnected everything but the fan and the light. Then I sealed everything in the freezer with caulk so the fan would suck from the fridge better. Next I cut a hole below the crisper and mounted the evaporator and a drip pan. I drilled a bunch of holes in the crisper plate for condenser airflow and mounted the compressor and condenser on there and she was ready for a test run!

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Old 08-09-15, 08:56 AM   #2
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Old 08-09-15, 09:06 AM   #3
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So it runs about 105 deg and the evaporator is covered in frost/water. Trouble is the compressor gets really hot and kicks out (I assume there is a thermal switch). I put a mechanical timer on it and tried 1/2hr on 1/2hr off and it still gets hot, even kicked out on one of the on times. Is the charge off? I never cracked the system and it has no valves so I don't know the pressures. The suction line is cool about halfway back to the compressor. I haven't messed with these types of compressors much but I do a lot of automotive a/c and when they are properly charged the suction is cold all the way to the compressor and even half the compressor is cold...
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Old 08-09-15, 09:11 AM   #4
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Oh and the compressor draws between 280 and 320 watts
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Old 08-10-15, 09:52 PM   #5
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Anyone have any idea why the compressor would run so hot? It does dry the food nicely and is working with the 1/2 hr on 1/2 off timing but I'm afraid I'm going to hurt the compressor. Maybe I'll get some valves so I have a better idea of what's going on...
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Old 08-11-15, 08:00 AM   #6
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My guess is that you changed the configuration. The combination of airflow changes through the heat exchangers and the raised evaporator temperature is causing superheated gas to not provide enough cooling to the compressor.

I just came across a fridge unit almost just like yours. Someone dropped it by cuz it don't do sumthin. I have ti troubleshoot it anyway, and I desperately need a large dehydration unit yesterday. I'll do what I do to it, and try to make it much like yours. Stay tuned...

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Old 08-13-15, 08:30 PM   #7
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I did a quick troubleshoot of the fridge unit. It looks just like mechanic's, but much more well worn. The compressor and condenser assembly isn't exactly the same: the condenser is the cinnamon roll style, which are known to rot and leak. It seems to operate, though.



The evaporator looks the same, and made some gurgling sounds when plugged in for a minute. However, the freezer circulation fan does not spin. That seems to be the root cause of how it tore up.


Since the compressor sounds ok and tries to circulate refrigerant, I will stick some access valves on the service pipes so I can read pressures. If the freezer fan is bad, I have more little fans laying around.

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Old 08-13-15, 09:02 PM   #8
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this is really most strange!

I looked at your code see that you have posted a heap of images, but I can't see a single one of them.


Anybody else having thos problem??

-AC
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Old 08-15-15, 12:14 PM   #9
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I've got to agree with Jeff, Mechanic. That configuration is going to produce a lot of superheat. The system either needs more refrigerant and/or a less restrictive metering device. That is a lot of current draw for a fridge that probably pulled half that as a when it was a refrigerator!

I've never built a dehydrator or crisper, but if you don't want to cut the lines, perhaps a dehumidifier ducted to the cabinet? Pull air from the top of the cabinet into the dehumidifier, then duct the exhaust into the bottom where you cut the hole?

Otherwise, you could perhaps throw in a piercing valve, and add a small amount of refrigerant (if you have it) until the superheat values come down. Might be worth a try.

Btw, I didn't see the pics either, Jeff
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Old 08-15-15, 06:43 PM   #10
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I edited my previous post with preliminary pics of the old fridge. No idea of the model number or brand, however, the kenmore, whirlpool, ge and others are 99.9% the same under the emblems. The model and field replacement part poster is on the top back of the unit, but this one is old and has obviously been bleached, then faded. I made out an R12 on the barely legible print. How old might this one be? At least it's not olive or some other color of baby poo...

I pried the freezer floor out and opened up the evaporator cover today. The foam was water logged, and immediately broke into a big piece and a few small pieces. Checking for juice, I found that this model, as most ancient units and lots of newer ones do, had a constant supply of power to the thermostat (red wire). From there, the thermostat directly switches power to everything except the interior light (orange wire). All of the defrost control stuff switches the neutral side of everything (white wires everywhere). This includes the defrost sensor switch, the defrost timer, and the defrost heating element. There is a yellow wire feeding the heating element, I imagine the defrost timer enables and disables power to the heater during certain times in the cycle.

The problem with this unit was not the fan. After removing the evaporator cover, I probed for, and found, 120VAC on the orange wire of the fan. The fan coil ohmed out at around 70 ohms dc. I disconnected the white wire from the fan and grounded that motor terminal straight to the evaporator (grounded for safety) using a voltmeter lead. Presto! the fan worked. I'm not going to troubleshoot this thing any further, except maybe checking the defrost sensor switch.



Note the condition of the white wire of the defrost heater, it looks like it may have found some moisture and arced a few times while it was supposed to be shut off.

I put a bullet piercing valve on the factory charging pipe to take a look at pressure, and to make sure there wasn't anything awry. At rest, the unit has 40-50 psig on the port. During operation, it quickly pulls down to below atmosphere until the condenser backs up some liquid, then rises to not much above atmosphere. This is normal for low side pressure on an ancient R12 unit.



The entire condensing unit and compressor lays on a sled in this unit, which can easily be yanked as one piece and relocated. The rails can be seen in the pic above; they screw into the corners of the frame at each end. I will reclaim the charge on this unit and relocate the whole thing inside the bottom of the crisper. I will cut the liquid line (the one running diagonally in front of the fan frame) close to the drain pan. The mfr put in a little loop in the liquid line to help warm the drain pan: how convenient for me! I can chop the loop out and splice the two ends back together.

I will braze the suction line (bluish from sweating) apart at the joint near the compressor and may be able to just bend the end upwards. There is a plug in the floor of the fridge box that lies directly above where the cap tube is zip tied to the suction line. The cap tube strainer feeds from the drip pan heater loop. If I'm lucky, the suction and liquid lines will feed right through the floor and be able to be connected without having to lengthen them. Either way, the deed will be done tomorrow. Then the unit will be ready for torture testing and drying some food (after a thorough pressure washing of course).

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