Amcor TC-120 Dehumidifier

[Richard_L]

I was given two Amcor TC-120 Dehumidifiers a while ago by a neighbour who was moving house. One was full of grass seed and the other was covered in oil but they cleaned up nicely and worked well for about 6 months. Now both appear to have developed a fault.

When turned on, they emit an audible CLICK and then visibly SHUDDER. This click-shudder sequence then repeats. The one I've used most does this about 150 times a minute to start with. The lesser used one only around 60 times a minute. I've stopped using them because of this problem but if I do leave them on long enough, the click-shudder behaviour slows and stops. Achieving normal operation might take anywhere from 2 to 15 minutes.

While the click-shudder is at its most intense, the dehumidifier draws up to 700W (measured with a plug-in power meter). The information placard on the back of the machine states power and current (at 240V) is 230W and 1.3A. After the click-shudder stops, power draw reduces to 18W and it appears to be working normally judging by the frost building up on the refrigeration coils.

I have no previous experience with dehumidifiers. Does anyone recognise this behaviour as a particular dehumidifer failure mode? Googling brings up very little of use about this model. About the only useful thing I've found is here http://www.fixya.com/support/t15686809-amcor_dehumidifer_tc120_circuit_board with the relevant bit being

It is not your relay. Mine did the same and the problem is the resistor that drive it goes short so the relay clatters as the circuit is trying to control it. The actual fault is the 78p153sp driver. You can change the transistor, a pnp will do the trick but the driver is dead. I'm currently looking for this IC and they're hard to find, cheap Chinese tat. So instead I'll likely fit a temp sensor that detects when the cooling coils reach about 4deg and switch the fridge off because shorting the relay will just cause the cooling to stay on and you'll get ice, it needs to cool, collect moisture, switch off, warm up and dump the moisture...crude but it works. This unit is worth saving.

Does anyone have any advice or insight before I start trying to disassemble it?

thanks,
Richard

[Seekonk]

A new 78p153sp would give you a Snowballs chance in a cat scanner.  It would have to be programmed.  A shorted resistor is a new one on me, never seen one. A bad power supply cap could could be causing the micro to reset and keep restarting the motor.  That 700W is actually pretty light for this kind of motor start.  Not much you can believe from those killawatties.  You could buy a rudimentary temp controller on ebay for less than $4 that could do what you say you want.  I don't doubt that the existing controller can be fixed and that it is something simple, but it sounds like this is not your thing.

[Richard_L]

Ah, so the only repair information already on the internet about this dehumidifier is probably nonsense! I did think that a resistor failing short rather than burning out and failing open was a bit odd but beyond that I hadn't even seen the actual control board when writing my question Thanks for the info about the start-up power of the motor looking reasonable.

Now, since writing my original post I've had the time to take off the front panel off of one of the machines and can now see where the control board is located. It's screwed to the underside of the plastic shelf that divides the inside of the machine in two. The compressor and water collecting tank are in the lower half, the refrigeration coils, fan and humidistat are in the top half. I don't think that this was built with disassembly or servicing in mind because there's only a few centimetres of clearance between the PCB and the compressor. I'm going to need a really stubby screwdriver and some smaller hands to get the board out. At the moment I can't see much of what's on it beyond two X2 caps and a relay, much less start probing around it...

[Seekonk]

I cringe at all the capacitor changers on this board, but it does seem likely that the main electrolytic on this board may be low in value.  Being that close to the compressor heat could have caused this problem. It makes sense that the high current draw of the motor on startup lowers line voltage resetting the micro.