Ok, does anybody know how low temp dehumidifiers are supposed to work?

I have a sears 70 pint Dehumidifier w/Electronic Touch Controls Model
#: 54701. Appears to be the same as the Comfort Aire brand. The
webpage description on sears.com doesn't say it's a low temp unit; but
the manual (which is for both units) does say the #701 70 pint unit is
a low temp unit, down to 45 degrees or such, while the #501 50 pint
unit is good down to 65 degrees (its web page says "Efficiency of
dehumidification is reduced when room temperature falls below 65
degrees").

I just finished replacing the burnt out fan motor, and I'm running it
without the housing on to see what's happening; and what's happening
is at 62-65 degrees, 60% humidity, the evaporator is a solid cake of
ice. This shouldn't happen to either machine at this temp, especially
not the low temp one, (which I think I have??) I figure this may have
contributed to the fan motor burning out.

The diagram stuck inside the thing shows a "reversing coil" and
thermistor connected to the circuit board. I assume the "reversing
coil" is the solenoid sitting on the tangle of tubing at the entrance
to the evaporator, and the thermistor is inside the crimped chunk of
large diameter copper tubing just below. I further assume that when
the thermistor gets near freezing, it triggers the coil which defrosts
somehow. I unplugged the coil from the board and put 110 volts ac on
it (it says 110v) and sure enough, it makes a "click" and the ice
starts melting. I don't know how long that cycle's supposed to take,
though, and after like 20 minutes the coil was starting to feel warm
so I terminated the experiment, even though the ice was only about
half melted. The evaporator immediately got to be an even thicker
block of ice.

So: first, is this the low temp unit? and why is the thing freezing up
at this temp, which is too high to freeze up at, even if it weren't
the low temp unit?
second, is the "reversing coil" for deicing? Is it supposed to kick in
when the thermistor is at 32 degrees and stay kicked in until it's
warmer? or something else?
third, what would the correct resistance values for the thermistor be
at both temps, so I can see whether it's dead, or else the board is?

thanks in advance.

Save yourself a headache. Take the Sears 70 pint unit and toss it in the
garbage. Mine was repaired/replaced every year for 3 years and even though
the refrigeration unit which just failed again is under a 5 year warranty I
dumped it. They are pure garbage. Lowes sells a Whirlpool that is noisier
but is supposed to work.


"z" wrote in message
ups.com...
Ok, does anybody know how low temp dehumidifiers are supposed to work?

I have a sears 70 pint Dehumidifier w/Electronic Touch Controls Model
#: 54701. Appears to be the same as the Comfort Aire brand. The
webpage description on sears.com doesn't say it's a low temp unit; but
the manual (which is for both units) does say the #701 70 pint unit is
a low temp unit, down to 45 degrees or such, while the #501 50 pint
unit is good down to 65 degrees (its web page says "Efficiency of
dehumidification is reduced when room temperature falls below 65
degrees").

I just finished replacing the burnt out fan motor, and I'm running it
without the housing on to see what's happening; and what's happening
is at 62-65 degrees, 60% humidity, the evaporator is a solid cake of
ice. This shouldn't happen to either machine at this temp, especially
not the low temp one, (which I think I have??) I figure this may have
contributed to the fan motor burning out.

The diagram stuck inside the thing shows a "reversing coil" and
thermistor connected to the circuit board. I assume the "reversing
coil" is the solenoid sitting on the tangle of tubing at the entrance
to the evaporator, and the thermistor is inside the crimped chunk of
large diameter copper tubing just below. I further assume that when
the thermistor gets near freezing, it triggers the coil which defrosts
somehow. I unplugged the coil from the board and put 110 volts ac on
it (it says 110v) and sure enough, it makes a "click" and the ice
starts melting. I don't know how long that cycle's supposed to take,
though, and after like 20 minutes the coil was starting to feel warm
so I terminated the experiment, even though the ice was only about
half melted. The evaporator immediately got to be an even thicker
block of ice.

So: first, is this the low temp unit? and why is the thing freezing up
at this temp, which is too high to freeze up at, even if it weren't
the low temp unit?
second, is the "reversing coil" for deicing? Is it supposed to kick in
when the thermistor is at 32 degrees and stay kicked in until it's
warmer? or something else?
third, what would the correct resistance values for the thermistor be
at both temps, so I can see whether it's dead, or else the board is?

thanks in advance.

On May 17, 4:06 pm, z wrote:
Ok, does anybody know how low temp dehumidifiers are supposed to work?

....
....
So: first, is this the low temp unit?

Since it has the reversing valve, that would be the only thing making
it a "low temp" unit -- it's there to work around the freeze up.

....and why is the thing freezing up
at this temp, which is too high to freeze up at, even if it weren't
the low temp unit?

Well, obviously it isn't too high a temp, is it? You already said
the temp was 62-65 which _is_ as I figure, under the 65 "magic
point". And, there's nothing absolutely guaranteed, I'm sure that any
of them will work at exactly 65 and start to freeze at 64 -- they're
just not made as precision devices.

The reason it's freezing is the coil temperature is dropping below
freezing -- doh!

second, is the "reversing coil" for deicing? Is it supposed to kick in
when the thermistor is at 32 degrees and stay kicked in until it's
warmer? or something else?

The thermistor is a control for the deicing feature, and the
"reversing coil" is just that -- it turns the cooling cycle into a
heating one temporarily as you discovered. Same thing as in the
exchanger unit of a heat pump.

third, what would the correct resistance values for the thermistor be
at both temps, so I can see whether it's dead, or else the board is?

Depends on the particular thermistor used -- a thermistor is a
temperature sensitive resistor and can have either a positive or
negative temperature coefficient; that is, the resistance can either
go up (positive) or down (negative) w/ temperature. You could try
measuring resistance across it's output and see if it varies w/
temperature swings as you operate the dehumidifier -- if it changes
from room temperature as the thing starts to ice up, it's undoubtedly
ok. They're pretty reliable devices, though, so I'd not suspect it as
a culprit first off...