Dehumidifier component - Page 1
Forum section: electronics / repair

author: valleyken
author_rank: Contributor
timestamp: April 12, 2025, 12:07:27 pm
content: Hi,- I am trying to repair a dehumidifier. Using it as a project to learn a bit more about electronics.- When I put the machine in dehumidify mode, the compressor seems to start for a second and then comes to a dead stop. Then it takes a little while before I can get it to do that again. Does that sound like a possible Relay problem?- I already tested the big capacitor with an ESR meter (lower left corner, below the power pcb). It seems to be okay.- The pcb is nicely labeled. There is some circuit diagram printed on the case cover too. I suspect the Relay (the black box to the left of that IC). But isn't there usually a 2nd Relay? What is that black box above the pcb ? It has 4 terminals, 2 cables attached to it. Nothing printed on it. Is that a relay too ?- What is the yellow component near the bottom of the pcb ? I'm guessing a capacitor ?- I know how to test resistors. I could test the capacitors also, probably have to take them out of circuit to do so. There are 3 transistors that I guess drive the relay ? But no experience with testing transistors.Any tips on where to start, are appreciated. What to test first, how to test?Valleyken

author: cozidinho
author_rank: Contributor
timestamp: April 12, 2025, 12:33:58 pm
content: I would assume the compressor wouldn't start if there was not enough gas pressure in the line, in an older non digital system. Could the stopping be part of any protection mechanism?

author: Gyro
author_rank: Super Contributor
timestamp: April 12, 2025, 12:49:07 pm
content: You may want to check the capacitance of the yellow capacitor at the bottom of the PCB (yes it is a capacitor). It looks as if the electronics are using a capacitive dropper to power the low voltage controller circuitry. If the capacitance value drops too low, there may not be enough current available to keep the relay energised (after a brief interval while the electrolytic reservoir caps discharge).It's a common problem with capacitive droppers, so worth checking. [Edit: The yellow cap does look physically quite small though, so it may just be an interference suppression cap - there are a lot of Electrolytics and an inductor grouped together which may be a non isolated switchmode supply].

author: seanf
author_rank: Contributor
timestamp: April 12, 2025, 12:58:59 pm
content: Quote from: valleyken on April 12, 2025, 12:07:27 pmMight have a klixon under the compressors terminal cover. May also have a current relay or PTC directly on the terminals.

author: CaptDon
author_rank: Super Contributor
timestamp: April 12, 2025, 01:21:38 pm
content: That sure is a lot of electronics for a dehumidifier. All the old ones just had a high current humidistat. I think some of the newer ones detect evaporator icing, airflow and dew point as well as 'tank full' conditions. With all of those sensors I still haven't seen small home units with low side / high side protection in the freon circuit. Newer units are famous for short life spans and leaks!! No one wants to repair and recharge a leaking unit. Usually cost more than a new unit. Those 1970 kelvinator units are still running but on their third fan motor replacement!!

author: valleyken
author_rank: Contributor
timestamp: April 12, 2025, 03:54:59 pm
content: - I identified that black box at the top with the 4 terminals. It had text on the bottom which I hadn't seen before disconnecting it. It is a 450V / 4 uF capacitor. I checked it out with the ESR meter and ESR = 0.18 Ohm and Capacity = 4 uF. So that capacitor should be good. The 2 cables connected to it, seem to go to the upper part where the fan is. I guess the 2 unused terminals are connected inside the capacitor to the 2 used terminals, just in case you'd want to connect something else.- I didn't know what a Clixon (overload) is. I will research that some more, see if I can find one. Or the Current Relay/PTC.- I assume that the compressor gas is okay. I saw a video of somebody recharging a compressor with gas, and it seems a bit dangerous to be doing it as an amateur. So if the compressor gas is the problem, it's for tossing it out. Probably too costly anyway, as suggested. But I still want to go over the power pcb, to learn more about the different components, and how to trace the signal flow coming in and going out from the pcb.- I will definitely test the yellow capacitor next. The blue and brown cables next to it are the 220V mains AC, so it makes sense that there is some circuitry next to it to drop the voltage to what the rest of the components need. There is a little fuse tube also (not visible, behind the brown cable). I tested it for continuity and it's okay.- Forgot to mention that the display pcb works okay, as well as the remote control. I can change the temperature setting, change the mode to high/low speed fan or humidify. It is normally connected to the wide (7-pin) connector at the top of the pcb (but currently disconnected). Next to it is a little red connector labeled "water", so I guess that's for some sensor to see if the tank is full. Another small (2-pin) white connector next to it, I don't know yet what that does, maybe connected to a temperature sensor.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: April 12, 2025, 04:01:10 pm
content: Quote from: CaptDon on April 12, 2025, 01:21:38 pmWhat dou you think about zeolite Dehumidifiers ?No motor, no freon, no noise.

author: TimFox
author_rank: Super Contributor
timestamp: April 12, 2025, 04:44:41 pm
content: Quote from: Coordonnée_chromatique on April 12, 2025, 04:01:10 pmI used zeolite in laboratory applications, recycling the used material in a lab oven.(Indicating zeolite with color change, e.g. “DrieriteTM” is handy.)Are there commercial zeolite machines for domestic use?

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: April 12, 2025, 06:21:01 pm
content: Hello valleyken,I have the same insights than cozidinho and CaptDon. Not 100 % sure that the issue comes from the electronic board.Check if there are somepressure switcheson the refrigeration fluid circuit.If a low gas pressure condition is detected, the switch on the compressor suction side protects the latter.If the high pressure switch triggers, the metering device (*) might be clogged.There's usually a PTC in the motor connector that helps the compressor to start with the starting capacitor.The klixon is inside the compressor : it is not accessible.But usually you can hear the clic if the motor magnetic coil is overheating.(*) in this case it is likely a vanilla capillary pipe

author: DavidAlfa
author_rank: Super Contributor
timestamp: April 12, 2025, 07:14:58 pm
content: I've never seen dehumifiers with pressure switches.Check the electrolytics, might explain this issue, the extra load from the relay might drop the voltage too much.The yellow part seems to be a fuse.Be careful as the low voltage part isn't isolated from mains, don't get fooled because you saw a 16V cap somewhere, you'll touch 240VAC.Don't overlook the buttons, I had several of them failing on me because of moisture getting in the switches.They read 100K ohms or more when inactive (Not pressed), but that was enough.

author: valleyken
author_rank: Contributor
timestamp: April 12, 2025, 07:33:34 pm
content: - There is this little gizmo, next to the compressor. Looks somewhat like a motor to me. Is that the motor connector where the PTC might be ? I wanted to take it out for a better picture. But there is 1 screw behind it that's very difficult to reach.- Right behind it, there is a little black "bulb" around the copper pipe, with the zip tie around it. Not sure if that's one of the switches you mentioned ? Or some kind of sensor I guess?

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: April 12, 2025, 08:12:50 pm
content: The black bulb (insulation ?) might hide a NTC temperature sensor. It is just touching the copper tube (thermal contact).Apressure switchhas its sensitive element directly in contact with the refrigerant fluid. But some vanilla systems do not have any pressure switch. It depends on how the designer wants to be on the safe side or rather keep the costs down to a minimum.If any, the PTC is inside part 'a1' (see diagram 'LST' on the last page of the attached document).Of course, your system might be slighly different : it depends on the compressor brand and model #.The small motor you pictured is ashaded pole motor. It can be used to drive a fan or a small water pump. The compressor is usually amuch biggerbeast.

author: Coordonnée_chromatique
author_rank: Frequent Contributor
timestamp: April 13, 2025, 05:34:39 am
content: Quote from: TimFox on April 12, 2025, 04:44:41 pmDelonghi DNS65 and DNS80 are great appliances, i've tested those with a compressor and find them too noisy for a domestic use.I don't know why compressor type still exists, i definitely don't understand this world

author: valleyken
author_rank: Contributor
timestamp: April 13, 2025, 07:17:02 am
content: - Oh, I guess the little shaded pole motor must be attached to a water pump to remove the condensed water. The water seems to accumulate in the bottom part of the machine, which doesn't have a removable tray to get rid of the water. There is a drain pipe at the back, which has a rubber cap on it now, but it looks like you can attach a hose on there. Not sure if the water is actually pumped out, or just flows out through gravity. Probably a pump. I should check if it's somehow connected to the connector labeled "water".- The compressor (to me) is what looks like a gas cilinder, in the bottom part of the machine. I don't really see any motor connected to it, but it's difficult to see in the tight space.There might be a motor above the cilinder, but that part is covered by styrofoam which is attached with screws. I assumed that there is a motor for the fan in there. But I should open up the styrofoam to see what's under there. Might be a whole other bunch of stuff under there that I didn't know about.

author: eurgenca
author_rank: Regular Contributor
timestamp: April 13, 2025, 08:26:19 am
content: Where the black cable (2pin) with white connector go?

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: April 13, 2025, 09:31:38 am
content: Hello valleyken,Quote from: valleyken on April 13, 2025, 07:17:02 amThe compressor looks likethis?In the affirmative, don't look for any external motor : it is an hermetic compressor, so themotor is inside the black cylinder.Unless you're a warrior, the compressor is an non serviceable part. If defective, it needs replacement.As suggested by eurgenca, mesure the resistance value of the sensor under the black insulation. 1 kor 10 kmight be suitable ballpark values.Talking about the electronic boardThere are some changes since 2015 on the 'LC-BSKT-JY-P' motherboard.Vendor 1Vendor 2µC and the voltage regulator (IC1) are now likely on the solder side because those are now SMD packages.Some versions of the motherboard are not fully populated : the 'PUMP' and 'STF'(*) faston connectors (and upstram TRIACs) are missing.If a replacement is required, ask the vendor to supply the fully populated motherboard.Not an open source device(*) cycle inversion solenoid/valve : allows the appliance to act as a heat pump during the cold months

author: valleyken
author_rank: Contributor
timestamp: April 13, 2025, 04:21:47 pm
content: - The black cable with the white 2-pin connector, is labeled N_T, and seems to be a temperature sensor that is clipped on the radiator-looking part at the top part of the machine. If I understood correctly, it's to prevent ice from forming on there (?) or maybe to check if it's overheating. Not real sure what it does, but pretty sure it's a temperature sensor.

author: valleyken
author_rank: Contributor
timestamp: April 13, 2025, 04:30:35 pm
content: - Yes, the compressor looks something like that. Attached 2 pictures of the label on it. There is a pipe (and some other stuff) in front of the label, so it's the left and right parts of the label.

author: valleyken
author_rank: Contributor
timestamp: April 13, 2025, 07:27:05 pm
content: - I desoldered the yellow capacitor (from the bottom of the control pcb). It says it is 0.1 microF. My Fluke multimeter reads 100 nanoF. So that's the same, if I'm not mistaken. But my Peak Atlas ESR70 meter says it is "open circuit or low capacitance". So now I'm not sure if the ESR meter can't read that low a value? Or if it's really broken?- Also there seems to be no + or - indications on the capacitor, nor on the pcb where it was soldered. I thought caps always need to be soldered in the right direction. So, not sure which way to put it back. I think I remember which way the text on the capacitor was facing, but I should check if I have a picture that shows it, to be sure.Edit:- This seems to be a "film capacitor", which can be soldered in any direction. Unlike "electrolytic capacitors" that need to be soldered in the correct direction of the + and - legs.- I bought a new 0.1 uF capacitor. But it also tests as "open circuit or low capacitance" with my ESR meter. From doing some research, I learned that ESR meters are rather used to test electrolytic capacitors. Film capacitors usually have a very low ESR value, so the ESR meter might not always be able to measure it. Or in the case of my ESR meter, it will just say "low capacitance". That doesn't mean that it's bad though. It's just a capacitor that has a very low capacitance, compared to electrolytic capacitors.- I have resoldered the yellow capacitor to the pcb, and consider it as not being the problem. Next I'm trying to test the relay. And probably give the electrolytic caps a quick check with the ESR meter also.

author: abrasumente
author_rank: Contributor
timestamp: April 13, 2025, 09:22:32 pm
content: Sounds to me like the compressor is either locked up, shorted, or hitting thermal overload.Grab a clamp meter and check the amp draw of the compressor when it starts. It should have a tag on the equipment that tells you what LRA is. If it gets close or exceeds that value and stays there for longer than a second or two, she's toast.Check the resistance of the compressor windings with it completely disconnected from the circuit. Should read like 2, 4, 6 ohms or similar values between pins. If one of em reads high resistance, it's done.You can check if it's hitting thermal overload by trying to start it, then killing power and checking across the pins of the compressor to see if any of them read open. Even these little appliance compressors usually have thermal overload protection. If it's kicking off on thermal, it's likely low or out of refrigerant.Please be careful working on this equipment. R290 is incredibly flammable- it's essentially refrigerant grade propane.

author: indeterminate
author_rank: Regular Contributor
timestamp: April 13, 2025, 10:39:37 pm
content: As aboveThere is usually a start/run capacitor in a metal can that could have failed.probably mounted somewhere near the compressor

author: valleyken
author_rank: Contributor
timestamp: April 14, 2025, 08:08:19 am
content: - I tested the big "metal can" capacitor that is near the compressor, with an ESR meter. It seems to be fine. This dehumidifier is my brother's, and he also replaced the capacitor with a new one he ordered. But since it didn't fix the problem, he sent the capacitor back and re-installed the original one. But you are right that it is one of the first things to check, the usual suspect.

author: seanf
author_rank: Contributor
timestamp: April 14, 2025, 09:10:11 am
content: Some of these small compressors need the pressure to be equalised between the high and low side of the refrigerant circuit, so that it starts under low load.Looks like Rechi uses a permanent split capacitor motor.You might find some info in their catalogue, like capacitor size, amps and such.https://www.rechi.com/folder/2025%E5%B9%B4%20%E5%A3%93%E7%B8%AE%E6%A9%9F%E5%9E%8B%E9%8C%84.pdf

author: valleyken
author_rank: Contributor
timestamp: April 16, 2025, 10:43:13 am
content: I did check the Relay. And it seems to be okay.- It clicks when I connect it to a 9V battery. In rest state, there is no continuity between the pins on the Load Side. When activated, it shows a low resistance of 0.3 Ohm. Just like it should be.- The resistance on the Coil Side is 262 Ohm. That is higher than the 50 - 200 Ohm range that was mentioned in videos I watched about relays. However, those videos were mainly about automotive relays. When I looked up the datasheet for my specific Relay, it shows that the Coil Resistance should be 270 Ohm. So the measured value seems to be okay.