Dehumidifier turns on but doesn't collect water (Solved)

Thread Starter

Bassquake

Joined Feb 16, 2018
86
I want to save a dehumidifier (Swan SH3021) from being thrown out but it doesn't seem to collect water.

It turns on, fan turns on, and compressor seems to turn on. But, looking at the wattage meter it draws 41W when fan is on, then every minute and a half, it'll jump to around 1180W for 15 seconds, then compressor turns off, until 1m 30s later, it'll turn on again for 15s and so on. Not sure if that's normal as I've never really used one before.

The wattage jump seems a bit high as the label on the case says 430W max. Have attached a couple of images. Help appreciated.
 

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Tonyr1084

Joined Sep 24, 2015
7,943
Without laying hands on the unit I'd say the compressor is frozen. If it's turning on then off for a minute and a half then it's trying to start but can't then that sounds frozen.

Leave it alone for 30 minutes, let the pressure balance out, then turn it on. If the compressor doesn't start then it's frozen. Likely fodder for the fill.
 

MisterBill2

Joined Jan 23, 2018
18,934
What I see is the compressor not really starting, but rather drawing the stall current. So the first step will be to check the starting circuit. If the start never engages then it will not start, but it will draw stall current, while if the start never disengages then it will stay in the starting current phase until the over current protector switches off. So if you are able to disconnect the capacitor during that 15 or so seconds, and it keeps running for a while, then that is the problem. Without the run capacitor portion it will probably not make enough power to keep running once the pressure rises.

If the freon has leaked out it will have a much smaller load and so will start and run but not cool.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
86
What I see is the compressor not really starting, but rather drawing the stall current. So the first step will be to check the starting circuit. If the start never engages then it will not start, but it will draw stall current, while if the start never disengages then it will stay in the starting current phase until the over current protector switches off. So if you are able to disconnect the capacitor during that 15 or so seconds, and it keeps running for a while, then that is the problem. Without the run capacitor portion it will probably not make enough power to keep running once the pressure rises.

If the freon has leaked out it will have a much smaller load and so will start and run but not cool.
You might be right. I opened up the electronics panel and looks like the large capacitor has popped and leaked some grey stuff out. Attached couple of pics. Ill pull it out (after shorting it) and replace it to see if it'll work again.
 

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Ian0

Joined Aug 7, 2020
10,000
I used to do technical support for a HVAC firm, and by far the most common reason for dehumidifier not collecting water was. . . . .dry weather. (Yes, we do occasionally have spells of dry weather here in Britain).
When a spell of dry weather appeared we had a competition between my colleagues for who got the first "dehumidifier not collecting water" telephone call.
 

Tonyr1084

Joined Sep 24, 2015
7,943
The failure description said that it draws a lot of current when it should start, but it never starts. Then after it gets hot the thermal protection kicks in and shuts off current to the compressor. When that cools back down it tries to start again.

I think @MisterBill2 has it. Blown starter capacitor as the TS has shown us. Wish I'd have thought of that. Good call.
 

MisterBill2

Joined Jan 23, 2018
18,934
An electrolytic might work, I have not tried doing that.I have made a furnace blower run whan the cap for it was not quite enough, bt adding a collection of parallel 0.47 MFD capacitors across the inadequate run capacitor. Mostly 400 and 600 volt rated caps from a nearby used parts box. That fix lasted for several years.
some symptoms become obvious when you see a few of them, and understand how stuff actually works.. That was my "secret", for doing industrial machine fixes for quite a few years. Refrigeration is simpler than most production machines.
The dehumidifier is supposed to make the condenser coils at the compressor heat up, so that after the heat is removed then the refrigerant can evaporate and absorb heat by being cold, and the moisture will condense into water and be drained away. (There you have the explanation with no math and no equations.)
 

Thread Starter

Bassquake

Joined Feb 16, 2018
86
An electrolytic might work, I have not tried doing that.I have made a furnace blower run whan the cap for it was not quite enough, bt adding a collection of parallel 0.47 MFD capacitors across the inadequate run capacitor. Mostly 400 and 600 volt rated caps from a nearby used parts box. That fix lasted for several years.
some symptoms become obvious when you see a few of them, and understand how stuff actually works.. That was my "secret", for doing industrial machine fixes for quite a few years. Refrigeration is simpler than most production machines.
The dehumidifier is supposed to make the condenser coils at the compressor heat up, so that after the heat is removed then the refrigerant can evaporate and absorb heat by being cold, and the moisture will condense into water and be drained away. (There you have the explanation with no math and no equations.)
Thanks but I've ordered a 7uF replacement. I guess the 5uF (same type) won't be sufficient.
 

MisterBill2

Joined Jan 23, 2018
18,934
It might work, but using the correct motor-duty cap is the right choice. IF there is a starter relay you should verify that it is functioning correctly.I did not see one in the diagram, but it may be different than that.
 

Janis59

Joined Aug 21, 2017
1,855
Once long ago I was working every evening after the main job into firm what imported trashed refrigerators from Scandinavia, my task was to repair it and then they sold out some 4x cheaper as new. Yet those days none had a microprocessor inside I bet the defect list is still the same.
1) Put the ammeter into motor circuit. If it shows at start about 5A shortly it is OK, but if for longer period there is over 2...3 A (we have 220 V, thus at US 111 V network the values may be twice larger), it means the short circuit in motor windings. Compressor must be shifted.
2) Amperes are high, but motor not running - probably start relay is broken. Simulate it by screwdriver - just push for second the ignition wire to the work wire and then release. If motor starts running, claim the start relay. This relay may exist in two versions - with electromagnet - coil and moving core. Probably it have been overheated and plastics clinched a core. Must be shifted, not repairable. Other version is piezo-ceramic. If not work, probably ceramic is crushed. Just shift it by new. When buying the new, must pass the work current plus minus 1/2 Ampere to Your motor Amperage.
3) Motor runs with small amperage but no cold. Freon gave gone. Somewhere is leak. Apply the leak tester to see where, solder (propane+oxygen and torch) by brass if possible, if aluminium, then TIG. 99.99% of cases the leak is from the aluminium parts. Then fill by anew and sniff with leak tester carefully. Motor runs with high amperage, in output is high pressure You see by the temperature at compressor outpot pipe, but no cold. Means somewhere the freon flow is clogged. First - somewhere is collected the water condensate. In have to not be, but if at charging the vacuum pumping was done too short, then resident water still may be inside, and then it freezes or into zeolite filter (looks like a short sausage), or in capillary tube inlet (looks like the thick copper wire coiled around filter few turns). Thus try to warm up with a cigarette lighter this filter for less than minute. If system de-cloggs, That is a relatively bad sign, because defect will repeat after some time, until re-charge the refrigerant. But at lest it works again.
4) What about temperature sensor? Probably it shows wrong. If the pressure/sylphon type, then it is VERY frequent defect. Just short it. If everything revives, then shift it by new.
 

MisterBill2

Joined Jan 23, 2018
18,934
Certainly post #13 is a useful analysis scheme for that sort of product, which evidently that production source had a common set of defects. It would be very useful in servicing similar refrigeration products.
Thank You to Janis59 for a useful tool.
 

Thread Starter

Bassquake

Joined Feb 16, 2018
86
Ok. Replaced capacitor and dehumidifier is pulling about 330W which seems normal, I feel warm air exiting out the vent and I see water on the heatsink but still no water in the collector bin. Maybe a clog somewhere?

Edit: Nevermind. I put front cover on and retried and now seems to work! Yay saved it from the tip, thanks to all. :cool:
 
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MisterBill2

Joined Jan 23, 2018
18,934
Certainly the airflow must pass over the cold portion of the dehumidifier system to condense the moisture, because the whole scheme is to have the cold part cooled below the dew-point of the passing air. That is how they work. Many dehumidifiers then pass that dried air over the internal refrigeration systems refrigerant-condenser coil as a means of improving efficiency. The result being that the dried air exits a bit warmer than it entered, but much drier.
 
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