Dehumidifier anti-icing switch

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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 ...
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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.
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Doug Miller wrote:

Model AD40G1 Looks like this:
http://images.fixya.com/W/Whirlpool/177x150/20825845.JPG
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.
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.xxxyyz.com> wrote:

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
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Evan wrote:

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.
http://www.appliancezone.com/ShowProduct.aspx?id824&AspxAutoDetectCookieSupport=1 P/N 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?

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Evan wrote:

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?

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Glad to hear a kind word, now and again. Got one right, for once!
Very often, a machine is designed for some air flow value. If you reduce the air flow, you get icing. This also happens in air conditioning devices.
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Stormin Mormon wrote:

You have repaid me for one time pointing to a reference about how the human teeth are numbered.
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I'll admit I don't remember that moment. But, glad it worked for you.
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Stormin Mormon wrote:

sci.dentistry, I believe.
The point was it worked for you.
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la.xxxyyz.com> wrote:

Interesting ........ have been following this dehumidifier thread, so thanks for the follow up.
We have a very much used Sears type DH, got free. It worked OK for a couple of years and then didn't.
So, in order to keep basement area drier and protect tools bought a very similar new one. It works fine, not needed much in winter but it runs more during our cool summers. Not sure if new one has an anti- icing switch at all! Seems to be more a matter (with this newer one) of setting it correctly so it doesn't form a block of ice on the cooling coils.
last year took the cover off the older one and discovered that it was a problem with anti-icing switch; it was operating 'too soon' or 'too quickly'. Operating (switching to open) to cut off the compressor almost as soon as any slight hoar frost formed on the coils. So removed it and now the unit seems to operate OK. Must try it again as weather gets slightly more humid. Keep meaaning to test oit out inthe fridge/freezer to see at what temp. it opens!
On the topic of humidity. During our cool winters normal home heating raises the house air temperatures and the relative humidity is thereby lowered. We have electric baseboard heat which some claim is too dry'.
One could call this a miserable 'spring'. It's an indication however that 'something' IS happening to the climate. We are now getting more rain into April/May, than in the past, not snow.
For example there is a local holiday in this part of Canada on May 24th, where traditionally we go trouting; the equivalent one guesses of the more affluent 'Fly fishing'! Many people have an old fishing pole in the trunk of the car or cab of the pickup and the spawning season for trout is over mid month, so off we go with a few flies and or a tail bait with a worm on it.
ANYWAY........ the point is that on May 24th the weather could/can be anything from 50+ degrees to snow/sleet!
Also by the way; two points.
1) Is there any rule on which way the air goes through the unit? Presumably room air is drawn in the back through the coils and exhausted past the fan out the front? The fan motor only gets slightly warm anyway and is also cooled by the now drier/cooler air from the coils?
2) All the energy used by the DH (probably about 300 watts/hr?) Become a small amount of heat within the house? Right? There's no heat pump effect here because the whole unit is contained within the one room. Similar, say to a fridge, which operates entirely within the shell of the house.
Thanks to all for the postings.
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terry 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?

How do you know that that was "too soon"?

What is your measure of OK operation? Keeps running steadily or produces water steadily? If it isn't producing water, that is not OK, and the evaporator may be iced.
I think my DH may have been running iced up a lot without me knowing, since I had it connected to the drain by a hose and never had to empty the bucket anyway. So I couldn't tell whether it was producing water.

Hopefully you mean 300W, not 300W/hr.

I wouldn't say 300W is a small amount. That could easily cost 5 cents per hour ($36/month). And if you are using your air conditioner, it will be another 300W extra power used by the A/C.

It is a lot like running a window air conditioner with both ends inside the house.

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la.xxxyyz.com> wrote:

You said the switch opened in a freezer when it was -4F. That's obviously a LOT colder than it needs to be for ice to form. It's possible the ice by the evaporator never gets that cold. I wonder what temp they are supposed to open at? Also, depending on how often this thing runs, it might be wise to look into a new one. Todays energy star units are probably more efficient than a 12 year old unit.


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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.
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Matt wrote:

I just tested the switch in ice water. It does not open in ice water.
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It's clearly not doing its job. Perhaps a replacement switch can be purchased?
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Stormin Mormon wrote:

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

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.
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Matt wrote:

http://www.appliance411.com/faq/dehumidifierfrosting.shtml
too cold of ambient room temperature. Most dehumidifiers are not meant to be used when the room temperature drops much below 70F and certainly not below 65F (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.
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