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Fan always runs, speed doesnt change (low/high), setting humidity level doesnt impact...is this a control board or circuit board issue?

Fedder Model: A7DH45B2A Unit is removing water fine, just never shuts off. I always hear the fan running. Even if I turn it off, only if unplugged does it stop, don't recall it doing this before. Hitting low/high fan speeds seems not to make a any difference. Setting humidity level higher than current room humidity does not turn unit off. Humidistat LED display seems accurately showing 55-60%. Seems compressor always runs...don't hear it clicking off at all when raising humidity..I recall the fan and everything would shut off if I raise the level greater than the room levels. My guess is the "control brains" are not telling the unit what to turn on/off and when. The buttons all beep and the displays all seem working...so is this a circuit board or control board issue?

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Paul Bade

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Verify the humidity reading with another device. Perhaps the humidity sensor is dirty or bad.

Another possibility is the switching device that runs the compressor and fan is shorted. If it's a mechanical relay, the contacts may have welded together, or if it's a solid-state relay, it's got a punch-through or meltdown in a device junction. My guess is it's a mechanical relay since you mention it used to click on and off and now you don't hear that. The relay may be on the control board, or it may be mounted separately - I don't have a photo or diagram of the inside of your model available.

Posted on Jun 25, 2015

  • Anonymous Jun 25, 2015

    I believe these are pictures of the boards I could replace...will try to take a picture of mine soon as well.
    http://www.ebay.com/itm/FD2518-020-DEHUM...
    https://www.appliancedepot.com/maytag-de...

    I have a hygrometer in the house and will verify it next to the unit.

  • Paul Bade Jun 26, 2015

    If the hygrometer readings agree, that takes care of the sensor end of the system, and we can go on to the next steps.



    The photo of the relay board from Appliance Depot will be very helpful in troubleshooting. I'll refer to it in the following discussion. First, I note in the lower right corner of the board, there is a set of jumper pins for DEF and RUN. If the dehumidifier evaporator coils appear to be iced up, check your owner's manual for defrosting instructions; they may include doing something with these pins.



    Second (I didn't think of this until I tried to figure out why there are three relays on the board rather than just one or two), check the condensor (a radiator-like device next to the compressor) to make sure it isn't loaded up with dust. If it's too dirty, and there is a fan on it, a temperature sensor may be keeping that fan on high speed in an attempt to cool it down. That fan probably would also need cleaning, but be sure to clean it thoroughly; a partial clean would most likely leave it unbalanced, which would be noisy and hard on the fan bearings.



    If these two basic maintenance items don't fix it, you have a failed component. Unplug the dehumidifier and inspect the relay board. The relays are the three black plastic boxes with lots of printing on top. (I think the fourth black box is a capacitor in the line voltage circuit for one of the relays.) The larger relay (with the identifier RLY1 printed next to it on the board) is for the compressor, one of the smaller relays is for the evaporator fan (pulls humid air in and dry air out), and the third is perhaps either for a condensor/compressor cooling fan or a condensate water pump (most likely a fan).



    In the lower left corner of the board there are four black plastic diodes, D1-D4. They get AC power from a transformer plugged into the smaller two pin connector (CN1?) next to them, and convert it to DC. This is filtered and regulated by the two electrolytic capacitors (the cans with the printed plastic shrink wraps) and the voltage regulator IC in between them. The tops of these capacitors should be flat. If one of them is domed upward, the capacitor is failing or dead, and power to the controller will be out of specification. This could cause improper operation. There should not be any heavily burned areas visible on the board, especially not around the relays. The area around the voltage regulator may be somewhat darkened from heat.



    If things look good so far, disconnect the transformer connector and plug in the dehumidifier. NOTHING should run. The controller board will most likely also be dark. If a motor is running, you have a shorted relay. Replacement relays are available, and any decent electronic technician should be able to replace it. (I checked Mouser Electronics, and they have the compressor relay listed for $2.34, but it's out of stock and will not arrive until the end of September.)



    If the relays have passed this test, unplug the dehumidifier again, and get out a multimeter. The next step is to check the relay driver transistors (the half-round black plastic devices with three wires, marked T1-T3, just below the smaller relay on the right). The easiest way is to do a resistance check from the relay kickback diodes to circuit common. Circuit common is the wire on the unbanded end of D1 or D2; connect the black (common) lead from the multimeter here. With the multimeter set to its lowest resistance scale, touch the red (positive) lead to the wire on unbanded end of the orange and black glass diode next to the relay that stays on when it shouldn't (or just test all three in the same manner). The resistance should be very high or open. If it reads several ohms or less, the relay driver transistor is shorted and needs to be replaced. The part number is printed on the flat face of the transistor. I would also recommend replacing the corresponding kickback diode; it may have failed to do its job of protecting the transistor from the inductive kickback voltage produced when the relay is turned off, and it costs $0.10 or less (part number 1N914 or 1N4148; they're equivalent).



    If the relay board checks out, the refrigeration system is clean and defrosted, and you still have a problem, it's on the controller board or one of the associated sensors. Unfortunately, that's not as easy to reverse engineer from a photo as the relay board. At this point, the e-Bay package is a good bet, but ask the seller to put it in an anti-static bag or package before shipping. Only handle the controller and sensor boards by the edges; static electricity from your fingers can easily damage the chips on them if you touch the circuitry without first being in contact with circuit common.

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Mode: Dehumidifier Humidity Set Air Value:60% RH Fan Speed: = Low

NOTE: In the event of a power failure or the unit is switched 'Off', the most recent settings are retained and restored once the power is switched "On"/resumed.
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DRY MODE SELECTION: 1. The unit does not have to be switched on (opera- tional) to select/set a program. All programs can be selected with the unit in the "off" position.
2. Press the MODE button until the Dry symbol is shown in the mode area of the display. Note: Each time the MODE button is pressed, the setting will alternate between DRY (dehumidifier) and FAN (only) mode.

3. Press the or cursor buttons to select the desired RH% operating value. To select CONTINUOUS operation,pressthe buttonuntilthesymbol"--" appears in the SET AIR display. During CONTINUOUS mode operation, the humidistat (control) will be by-passed and the compressor will operate non-stop regardless of humidity conditions.
FAN SPEED SELECTION:

4. Press the fan symbol on the keypad. Each time the button is pressed, the mode selection will alternate between "High Fan" and "Low Fan" speed options. The fan speed you select will appear in the LED display; either a 4 blade fan symbol for 'high fan' or a 3 blade fan symbol for 'low fan' will be shown in the display area.

5. When all settings are complete, press the I/O button to start the selected operation (MODE) and the blue opera- tion light will illuminate.

FAN ONLY MODE SELECTION:
1. Press the MODE button until the fan blade symbol is shown in the mode area of the display. 2. Press the "Fan" symbol on the keypad. Each time the button is pressed, the mode selection will alternate between "High Fan" and "Low Fan" speed options.
3. When all settings are complete, press the on/off button to start fan mode operation and the blue operation light will illuminate.

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