Dehumidifier Problem

[GaryS65]

Have a great little dimplex dehumidifier but it stopped working so I decided to see what was going on. It is about 12 years old.

Now before it stopped working I saw the operation LED flickering a bit.
Now it doesn't light at all even though I've got power down to the compressor.

The fan motor runs perfectly.
Water bucket switch operates correctly,

I've got live coming down to the compressor 230v to earth.

I found the capacitor was only showing 1.4uF not 4uF so I thought I had sussed it. Alas no, new cap fitted an still no go.

Looked at the PTC relay. Got continuity across the overload. Got continuity at 40Ohms across the PTC thermistor. House temp currently 16°C.

Has this handy wiring diagram.

I'm half tempted to wire the compressor up on the bench just to check I'm not going mad.

If I put the amp meter on the blue wire coming to the compressor (common) I get no current draw at all.

 

[GaryS65]

I'm pressing the bucket switch in manually by the way hence why the red light is on.

 

[GaryS65]

So I checked the resistance between Common-Run-Start on the compressor.

No short to earth.
A:M 43 Ohms - A:C 26.8Ohms - C:M 16.1ohms

 

[GaryS65]

Sussed it. I'm getting a low voltage from the defrost board. Only 203V.

So some investigation needed...

 

[GaryS65]

Wiring the compressor direct from the humidistat works fine

 

[minimutly]

How do these defrost boards work - is it a simple cyclic timer or does it measure the coil temp then delay before defrosting?

 

[rtcosic]

Sussed it. I'm getting a low voltage from the defrost board. Only 203V.

So some investigation needed...

Beat me to it!

I bought one from Facebook Marketplace a few weeks ago for the garage. At first it whirred away like a little champ collecting at least 3 litres per day.

Then it didn't.

It has a temperature sensor on the condenser, which switches off the compressor when its temperature falls below c. 5°C. I found that with my Lidl thermometer thingy, SWMBO's hair dryer and a chilly afternoon's experimentation in the garage.

I would check that system first.

EtA: it didn't have any operating manual and the details I found on line didn't mention this.

 

[GaryS65]

Beat me to it!

I bought one from Facebook Marketplace a few weeks ago for the garage. At first it whirred away like a little champ collecting at least 3 litres per day.

Then it didn't.

It has a temperature sensor on the condenser, which switches off the compressor when its temperature falls below c. 5°C. I found that with my Lidl thermometer thingy, SWMBO's hair dryer and a chilly afternoon's experimentation in the garage.

I would check that system first.

EtA: it didn't have any operating manual and the details I found on line didn't mention this.

Yes my thoughts was the temperature sensor element of the defrost too. Not too sure.
It's back collecting water now, I've just bypassed the PCB. Will turn on for an hour then switch off.

I plan to test the relay on the board and also test the temp sensor with a cube of ice to see if the defrost light comes on.

At the minute the relay on the defrost board is open on both legs, which strikes me as odd. But I will check resistance later as that's the only reason I can see for only 203v reaching the compressor.

 

[GaryS65]

How do these defrost boards work - is it a simple cyclic timer or does it measure the coil temp then delay before defrosting?

Quite a lot going on, on this little board, temp sensor positioned in front of the air intake side of the evaporator.
Quite a few capacitors and resistors and two "chips" some sort of IC or something.

 

[knighty]

the the pcb just controls the defrost depending on temperature and you can't get spares it would be easy enough to swap it out for a different off the shelf temp sensor

most digital ones will let you set a temp difference and/or on/off temperatures separately... so it would turn off at 0'c and come back on at 8'C (or whatever... total guess at numbers there)