Dehumidifier anti-icing switch

[Matt]

Whirlpool household dehumidifier, about 12 years old.

Lately the evaporator has been icing up so that no water is produced.

Inspected the anti-icing switch while it was iced up: the base of the switch was pretty well covered with ice. The evaporator coil to which it is clamped was covered with ice too of course. There was some corrosion between the coil and the switch.

I removed the switch and hooked it to a continuity tester (digital ohmmeter actually). At room temp the switch is closed as expected. When I put it in a freezer (-4 def F or so) it opens as it is supposed to, which is unexpected. I mean the switch seems to be working, when I don't have any other explanation for the ice-up.

Should it be enough that the base of the switch is embedded in ice? I mean that should be enough to open the switch, shouldn't it? Or does it need to get colder than ice?

Has the switching temperature of the switch changed over time and gotten too low, even though it still opens at very cold temps?

I was thinking maybe the switch didn't have good enough contact with the evaporator coil, but gosh, if it is embedded in ice ...

[Doug Miller]

Clean the evaporator coil. I have two Whirlpool dehumidifiers of similar age (9 and 11 years), and that's what causes mine to ice up: dust building up on the evaporator.

[Matt]

Model AD40G1 Looks like this:

I fix a section of furnace filter inside under the grill, and change it every year or two, so both the evaporator and condenser stay pretty clean.

[Matt]

I just tested the switch in ice water. It does not open in ice water.

[Evan]

Just because you have a filter inside of something doesn't mean that the thing the filter is installed in never has to be opened up and cleaned every once and a while...

As to the switch you described not working when installed on the coil subject to the icing condition but working under your ideal test conditions and then again not working when you submerged it in ice water, could it be that some of the ice on the coil melts and flows into the switch ?

You could try replacing the switch but it also sounds like cleaning the coils with HVAC coil cleaner more often than never would be a good idea too...

~~ Evan

[Matt]

too cold of ambient room temperature. Most dehumidifiers are not meant to be used when the room temperature drops much below 70°F and certainly not below

65°F (depending on humidity level). There are however some models called "basement dehumidifiers" (see the link below) which are and could be used in cool room conditions.

air flow through the unit. If the fan motor is not turning fast enough (or at all) or the evaporator, condenser or filter (if used) is plugged, each could result in poor air movement.

[Matt]

It looks to me like the switch is sealed and is supposed to be waterproof. There is a sealant like epoxy or silicon around the wires where they go into the housing.

1168777

I am not opposed to that idea, but I don't know how to tell whether they are dirty enough for that. I can tell you that I can see between the fins easily.

There are some patches where dust is building up a little here and there, and I will remove that dust with a vacuum cleaner, but I think I can say that that is not going to increase the flow rate by 5% or probably even 2%.

To be brief: the coils look clean enough to me.

There is considerable dust on the filter. There are some small side vents anyway where air can bypass the filter.

Regardless of what is causing the icing, should it not be shutting down before it ices up?

[ransley]

I bet it needs Freon, its old.

[Stormin Mormon]

Please clean both the evaporator, and condensor while you have the cover off. I'd suggest a generous spritz of Simple Green. Wait five minutes, and rinse with warm water. Do this a second time. Use a nylon brush or tooth brush to remove any visible dirt and grime.

[Stormin Mormon]

It's clearly not doing its job. Perhaps a replacement switch can be purchased?

[Matt]

I am inclined to agree, since the switch stays on when immersed in ice water.

It is hard to think of a way that you are wrong on that point.

Somehow we are not getting much agreement though.

It's about $20, including S&H, which I am happy to spend if that will fix it.

[trader4]

Did you verify that the the rest of the system that the switch is connected to does what it's supposed to? Don't know how they all work, but one I recently worked on has a reversing valve, which actually reverses the system so it becomes a heat pump that warms the evaporator coils. I'd try connecting and disconnecting the two wires while it's running.

Also, the unit I worked on was icing up and the cause was the blower motor was shot. Normally, they should not be icing up unless it's in a cold environment. That's the difference with the low temp models, they have provisions to defrost if needed.

[Joe]

[Matt]

So you don't believe the anti-icing switch should go off when immersed in ice water? How is it going to prevent icing if it stays on at the freezing point?

[BQ340]

They are not precision calibrated switches, it may open slightly lower than freezing. Some have the operating range printed on them, any numbers on it that have a F after them?

MikeB

[Matt]

duh ... good question ... thanks ...

Here are the markings on the switch:

T-O-D

37TA32 31097 1168777 F53-30F J9850

Here is the product line:

offers proven reliability in a moisture resistant sealed design.

applications such as defrost termination and ice cube maker control. It is also applied in a range of heat pump and air conditioning applications.

I don't see anything in the product info that relates the part number to the temperature range.

As you hinted, there is that "30F" number, but that doesn't seem to match the temp ranges described in the product info.

[Stormin Mormon]

Since the dehum coated your old switch in ice, I'd not spend much more time in analysis.

[Matt]

Meantime I've gotten the idea that the switch might work by sensing the temp of the coil to which it is clamped, which would have to be below freezing to attract frost.

As I mentioned elsewhere on the thread, the switch bears a marking "F53-30F", which might indicate a switching temp of 30 degrees.

So I guess it could be that the switch would not turn off even when embedded in ice---if it is not making good contact with the coil. And it could be that if it were making good contact with the coil, it would turn off before the coil gets cold enough to attract frost---at a temp between the freezing point and the dew point.

If the switch is not making good contact with the coil, the hypothetical design above wouldn't work. As I mentioned, there is some corrosion on the coil where the switch is clamped.

[terry]

Agree ours (located in a cool basement) and which does not have an icing switch AFIK; ices up easily when temperature falls to about

50-55 F. But in winter, here, the humidity of the basement air drops any way and we just keep it 'turned back'. During warmer more humid summer (it never gets very hot here anyway) it works better with less icing. One change have made is to rewire the fan to run continuously while the unit is plugged in so that if ice does start to form the moving air melts it more readily.

[Matt]

You and some others (eg Stormin') were right that it was an airflow problem.

Thanks especially to anybody who suggested cleaning the condenser.

I was only looking at the evaporator, which was quite clean. I didn't notice that the condenser was fairly dirty. The airflow was such that air could get in past the filter when the filter got a little plugged.

I took the whole cover off and put the innards outside under the hose and sprayed water gently though the coils. Washed out some wet globs of dust. Not huge globs, yet of a somewhat gratifying size.

I also brass-brushed the evaporator coil where the anti-icing switch is clamped on. There was some green corrosion that might have been inhibiting contact between the coil and the switch.

The filter itself probably slows the airflow, maybe enough to cause icing when the filter gets somewhat dirty. The filter is not part of the OEM design, but is my bright idea.

See my post elsewhere on stopping the vibration on this model.

I put it all together with a clean filter, and it is running fine.

Not clear that the anti-icing switch is working though. Could be the improved air flow is enough to prevent the icing, and the switch hasn't needed to work yet.

I wrote:

was pretty well covered with ice. The evaporator coil to which it is clamped was covered with ice too of course. There was some corrosion between the coil and the switch.

actually). At room temp the switch is closed as expected. When I put it in a freezer (-4 def F or so) it opens as it is supposed to, which is unexpected. I mean the switch seems to be working, when I don't have any other explanation for the ice-up.

that should be enough to open the switch, shouldn't it? Or does it need to get colder than ice?

low, even though it still opens at very cold temps?

evaporator coil, but gosh, if it is embedded in ice ...