De-huey problems

[Devilman]

Hey all, hopefully some of you HVAC / Techie guru's can help me out here. I got an old Dehumidifier from way back, always worked good as gold etc.. until I moved it to a new location recently...

The unit still functions and extracts water just fine, the problem is the damn internal Humidity sensor now seems to prettymuch read 99% all the time (resulting in the machine running constantly).

I pulled the unit apart the other day and located what I *thought* (read - expected) to be the humidity and temperature sensors, however they are not behaving as expected..

Origionally I had thought the solid metal "tube" thermistor which was clipped into a copper tube soldered to the side of the evaporator was for general temperature sensing (the unit can report temp and humidity) however after playing around warming up the termistor etc.. and seeing no change in reported temps I can only asume this thermistor is actually a low-temp cut-off to prevent icing of the evaporator.

Clipped into the fins at the front of the unit was a small sensor which does indeed look like a standard humidity sensor, however its behaviour makes no sense... When I breathed on the sensor (the same way you would to clean your glasses) instead of the humidity reading changing, the temperature reading went up?!

I have taken the sensor apart and made sure it was all clean and dry inside, I even tried leaving the unit running with the sensor in the exhaust flow to dry it out and still no changes to the humidity reading.

I'm a bit lost at this point because frankly I was expecting a fairly simple problem such as bad sensor etc.. but the fact its affecting the temperature reading, when its clearly a 2-pin humidity sensor makes NO sense at all to me, so can anyone here offer any help or suggestions?

I know I could replace the unit for a new one, but its still functioning perfectly... just won't turn itself off at a set point, due to always thinking humidity is at 99% and with Xmas fast approaching funds are a little tight to be replacing the unit, so any help would be greatly received

 

[Granger2]

You could use one of these:
http://www.grainger.com/product/DAYTON-Dehumidifier-Control-1UHG2?s_pp=false&sgAttributes=
Cheaper than a dehum.

The humidistat went out on my old LG unit, but I can use it with the add on, and it works fine. I moved it to my drying room for light duty service. Good luck. -granger

 

[queequeg152]

the soldered copper bulb you referred too is probably part of the thermal expansion valve assembly.
this must be a nicer dehuy, because from what i recall, most are cheap cap tube systems.

your humidity sensor is likely mounted to the same PCB that controlls the display and interface board.
its likely an ultra cheep capacitive type pcb mounted sensor.
you COULD spend hours on digikey trying to find a replacement, and soldering said replacement into the old board, but i would either take granger2's advice and get a separate dehumidistat, or buy a replacement board.

though i recommend you stay away from the cheap digital type sensors. get a regular battery powered dehumidistat or thromstat/dehumidistat from any hvac store. you could also buy a decent hair type hygrometer to compare against. a decent hair hygrometer will be pretty damn accurate, and readily calibrated.

 

[Devilman]

Queeg : I think you missunderstood when I said about the soldered tube, it's not a TEV system, the "tube" in reference is just a "holder" for the thermistor to slot into.

Granger : Yeh that looks like a good idea, but not sure it'll work for me, this de-huey has to be turned on every time its connected / reconnected to the power, so having a humidistat or similar to turn the power on / off... I have yet to find a way to make it work.

 

[queequeg152]

i see. yea you are probably right about low temp cutoff... it would prevent the compressor slugging on liquid refrigerant i guess.

do you have any pictures of this sensor? im assuming you have looked everywhere for another sensor? have you looked at the controller on this particular unit?

a humidity sensor does not need to be inside the airstream.

humidity gradients equilibrate relatively quickly. IE you can dehumidify a bedroom in the center of your home, and the surrounding wetter air will readily exchange moisture with the dry air such that you could probably only measure a single digit humidity differential.

my point is that the sensor could be hidden away in a sheltered area, with just a few holes for air to move into and out of.

 

[Devilman]

I will try to snap a few pics later on, of both the sensors and the unit itself..

I have taken the control board out from the case and checked in the hope they had mounted the humidity sensor there but nothing of the sort.

What really baffles me to be honest is that the sensor in the airstream (which definitely looks to be a humidity sensor) is causing temperature readings to change, which would suggest it is infact the air-temp sensor, but if that is the case, I have no clue at all where they hid the humidity sensor, as I have followed back every set of wires from the control board

 

[queequeg152]

interesting. ive honestly had almost 0 experiance with dehumidifiers. perhaps humidity is measured in the same manner of that of a sling psychometer?

is the sensor in question perhaps in contact with the evaporator?