Dehumidifier compressor thermal cut-out?

[terry]

Some advice please.

Smallish floor mounted dehumidifier on casters, about size of a small filing cabinet.

The colour and style of the overall unit suggest it was the sort of thing sold by say Sears some 20+ years ago. (We also have a newer one that is very similar but different colour and details).

Problem. Compressor runs but after a few minutes cuts out.

Problem has been tracked down to the compressor itself. It's a typical fridge type sealed compressor. The compressor is marked as follows;

"aose a" , "115 v 60 Hz", also "A5160A 144CG25". The compressor is also labelled "Thermally protected".

After checking and bypassing all other parts of the circuit (the humidistat, drip pan float switch and some sort of 'cut-out' clipped to the output end of the cooling coils are all OK) it is found the compressor runs but shuts down after several minutes without getting particularly warm!

On the side of the compressor, plugged into two of the three pins projecting from the sealed unit, is a typical compressor starter relay marked [FSP] "920235" and "960A042-172" and "P4S".

Adjacent to the starter relay under the same cover and in series with the hot lead from supply to the starter relay is a round bi-metal device which the mounting clip presses against the outer surface of the compressor. It is marked Klixon and "MR26ALK-3164" and "T.150-IK45 [FSP] 950234". We presumed this circular device to be a bi-metal thermal protection switch. However when it is temporarily by-passed the whole unit runs, the cooling coils start to form frost but the compressor still cuts out after a few minutes.

Is there another thermal protection circuit inside the sealed unit???? And if so there is presumably no way for a DIYer to fix it, nor would it be worthwhile/safe to attempt. Correct?

We were going to chuck this unit but decided to give it another try before doing so. Any knowledgeable advice would be most welcome.TIA.

BTW the unit is marked R12 (refrigerant) so if we dispose of it we will call the Environment/Recycling people to determine where to take it.

Although in one middle - eastern country where we were for several years have seen car AC systems 'serviced' by letting the refrigerant blow off and then recharging the whole thing!

[Stormin Mormon]

It's very possible the start relay is bad. Not a likely problem, as it does run for a few seconds or moments. Sounds more like the compressor berrings are worn out, and the internal friction is too great for the motor.

If the problem were dirty condensor, the compressor would be too hot to touch. You ruled out several of the other possibilities.

There are hard start kits made for compressors, but might not be worth the bother. An appliance shop may be able to fit it with a hard start kit. And, it may keep doing the same problem.

[stan]

---------------------------------------------------------------------------=

-------------------------------------------------------------------- Thank you Christopher: Your reply is most appreciated.

Yes the unit does run for about a minute or two; so one thinks "Ah OK, it's going to work OK" but then it cuts out. Also it does seem to stop rather abruptly/roughly (the compressor makes quite a physical kick as it stops!) which might suggest bad bearings?

Or in other words it's worn out (after all I did get it for nothing although it did seem to work sometimes for a couple of years!).

Didn't think of a defective starter; cos that looks OK and seems to test OK? But may have another used starter from an old fridge, somewhere that can try.

Or maybe can simulate the action of the starter relay.; which I think is that the relay pulls up by the higher initial current of the compressor motor at rest, which closes a contact to the starting winding. Once motor is running the relay presumably drops back opening the starting contact? Like, on a very small scale the procedure for manually starting those old style big industrial motors!

Thanks indeed for the suggestions and about possibility of bad bearings; hadn't thought of that.

My regards; thank you. terry

PS. If successful will post follow up. .

[Stormin Mormon]

So, the starter tests OK. How did you test it?

[stan]

Follow up.

Well it is NOT the compressor internal or external thermal cut-out/ protection; I should have realized earlier there IS another element in the circuit!

Most of the controls, humidistat, drip pan float switch, etc. are in the live lead to the compressor circuitry. However there is one item which appears to be some sort of temperature sensor which is/was wired into the neutral side of only the compressor!

It is circular, sealed, has no means of adjustment and was clipped onto the exiting end of the cooling coils.

The printing on it is very faint but appears to be "37T32 29531 59-20" Also "F?20009-052 and 201?M?73" But that last group of 8 characters is very indistinct indeed.

After removing it the rest of the unit operates fully, it starts normally and frost quickly forms on the cooling coils. So the immediate conclusion was that this 'cold control' switch is maybe faulty or operating too soon at too high a temperature?

So a question might be; is this gadget supposed to open the compressor ctcuit to allow, say, the coils to periodically defrost and/or is it opening at much too high a temperature.

If opening at too high a temperature maybe it should be reinstalled and located differently so as to not operate so soon?

Any further advice most welcome.

Also the knob is broken off the humidistat but that can be repaired. Adjusting the humidistat (basicall a micro-witch with a sensor) shows that it is working.

Further advice welcomed.

[Don Young]

Follow up.

Well it is NOT the compressor internal or external thermal cut-out/ protection; I should have realized earlier there IS another element in the circuit!

Most of the controls, humidistat, drip pan float switch, etc. are in the live lead to the compressor circuitry. However there is one item which appears to be some sort of temperature sensor which is/was wired into the neutral side of only the compressor!

It is circular, sealed, has no means of adjustment and was clipped onto the exiting end of the cooling coils.

The printing on it is very faint but appears to be "37T32 29531 59-20" Also "F?20009-052 and 201?M?73" But that last group of 8 characters is very indistinct indeed.

After removing it the rest of the unit operates fully, it starts normally and frost quickly forms on the cooling coils. So the immediate conclusion was that this 'cold control' switch is maybe faulty or operating too soon at too high a temperature?

So a question might be; is this gadget supposed to open the compressor ctcuit to allow, say, the coils to periodically defrost and/or is it opening at much too high a temperature.

If opening at too high a temperature maybe it should be reinstalled and located differently so as to not operate so soon?

Any further advice most welcome.

Also the knob is broken off the humidistat but that can be repaired. Adjusting the humidistat (basicall a micro-witch with a sensor) shows that it is working.

Further advice welcomed.

I have not read this entire thread but it seems to me that your unit might be low on refrigerant. I don't think the coil temperature should be below freezing (frosting). If the coil is frosting at the inlet (small pipe) end and is a lot warmer at the other end, it is almost surely low on refrigerant.

Don Young

[Stormin Mormon]

Follow up.

Well it is NOT the compressor internal or external thermal cut-out/ protection; I should have realized earlier there IS another element in the circuit!

Most of the controls, humidistat, drip pan float switch, etc. are in the live lead to the compressor circuitry. However there is one item which appears to be some sort of temperature sensor which is/was wired into the neutral side of only the compressor!

It is circular, sealed, has no means of adjustment and was clipped onto the exiting end of the cooling coils.

CY: Sounds a lot like a freeze stat.

The printing on it is very faint but appears to be "37T32

29531 59-20" Also "F?20009-052 and 201?M?73" But that last group of 8 characters is very indistinct indeed.

After removing it the rest of the unit operates fully, it starts normally and frost quickly forms on the cooling coils. So the immediate conclusion was that this 'cold control' switch is maybe faulty or operating too soon at too high a temperature?

CY: Perhaps. Since the freeze stat trips too soon......

So a question might be; is this gadget supposed to open the compressor ctcuit to allow, say, the coils to periodically defrost and/or is it opening at much too high a temperature.

CY: If it's what I think, it's to prevent the evaporator coil from turning into a block of ice. The coil only needs to be in the thirties or forties to condense water out of the air.

If opening at too high a temperature maybe it should be reinstalled and located differently so as to not operate so soon?

Any further advice most welcome.

CY: Might be the unit is low freon, and getting cold too fast, or the freeze stat is too sensetive. I'd be tempted to try a couple wraps of electrical tape around the tube, and then put the freeze stat back on. Maybe that will slow it down.

Also the knob is broken off the humidistat but that can be repaired. Adjusting the humidistat (basicall a micro-witch with a sensor) shows that it is working.

Further advice welcomed.

I have not read this entire thread but it seems to me that your unit might be low on refrigerant. I don't think the coil temperature should be below freezing (frosting). If the coil is frosting at the inlet (small pipe) end and is a lot warmer at the other end, it is almost surely low on refrigerant.

CY: It's normal to frost a bit where the cap tube goes into the evaporator. But, most or all of the evaporator (cold coil) should be cold.

Don Young

[stan]

Thanks Don: But don't think so! Now that I've got the unit to run without cutting out after each couple of minutes it forms a heavy coat of frosty ice evenly over the whole of the coil. The icing starts at the input end of the coil and then just builds all over it. Just like the other unit we have. That other unit especially when it is at a humidistat setting that is too low for the basement area temp. of around 55 to 60 degrees F builds up a layer of ice which and does not stop to allow it melt off.

With (what I will call the temperature switch) removed the unit runs continuously and all other aspects of the unit seem to be OK!

But I'm still not clear of the function of that device which was clipped to outlet pipe of the cooling coils on it's way back to the compressor! And was the only cut out in the neutral lead to the compressor! Maybe it's function is to sense that the coils have reached freezing? So then it stops the compressor allowing the ice to melt off the coils. Thereby accomplishing de-humidification?

Anyway tomorrow will place the humidistat where it is normally, directly in the air flow out of the unit, and see it how reacts when the unit is plugged in and is run continuously. Looks like am getting close to solution!

[Stormin Mormon]

Thanks Don: But don't think so! CY: Oh, why not!

Now that I've got the unit to run without cutting out after each couple of minutes it forms a heavy coat of frosty ice evenly over the whole of the coil. The icing starts at the input end of the coil and then just builds all over it. CY: Normally, that happens for the first few minutes, and then frost coat melts off. If the frost stays, the unit is probably low on freon.

Just like the other unit we have. That other unit especially when it is at a humidistat setting that is too low for the basement area temp. of around 55 to 60 degrees F builds up a layer of ice which and does not stop to allow it melt off. CY: I've seen ice blocks on the back of dehum.

With (what I will call the temperature switch) removed the unit runs continuously and all other aspects of the unit seem to be OK!

But I'm still not clear of the function of that device which was clipped to outlet pipe of the cooling coils on it's way back to the compressor! CY: It's probably a freeze stat!

And was the only cut out in the neutral lead to the compressor! CY: Well! That's all it has to!

Maybe it's function is to sense that the coils have reached freezing? So then it stops the compressor allowing the ice to melt off the coils. Thereby accomplishing de-humidification? CY: Yes! Exactly!

Anyway tomorrow will place the humidistat where it is normally, directly in the air flow out of the unit, and see it how reacts when the unit is plugged in and is run continuously. Looks like am getting close to solution! CY: Sounds like you need a new freeze stat! And I wore out my! exclaimation point! key!