waeco 40lt thermister not working again

dorian · Guru

RE: waeco 40lt thermister not working again

possumyvonne · Senior Member

Dorian, i can see what your writing but what does this all mean and where are you going with it
Hope you understand what im asking
Regards Peter

possumyvonne · Senior Member

Daryl, The pics you put up from Bob & Bev on doing the thermistor, is that how Waeco do it when they replace a Thermistor, reason i ask is because the one Bob has in the pic looks like the genuin waeco one , that i have
Would be interesting to find out
Regards Peter

dorian · Guru

If it is of any help (perhaps in future), here is a hand drawn circuit diagram for a Waeco CDF-40 (was it drawn by someone in this forum?):

www.eserviceinfo.com/downloadsm/54721/WAECO_CDF-40.html

There appear to be a few errors.

(1) I believe transistors Q1 and Q2 should be NPN, not PNP.

(2) I'm not certain, but I believe there should be a resistor between the thermistor and the 7.3VDC supply rail.

@possumyvonne, all I was trying to determine from my calculations was whether the Jaycar thermistor was a close enough match for the original Waeco one. Since you have opted for the original part, then the calculation for the alternative part is moot.

possumyvonne · Senior Member

The thermistor i did have in was a Jaycar one which only lasted about 12 months so will be interesting to see if the waeco one i bort lasts longer, i hope so
Living in qld the temp here is higher and the fridge and freezer need to be turned down more, i run my fridge on about 1c and freezer at -10, this is also because the temp inside the cruiser gets quite warm inside
I could run the air con which would help but when we are out walking for hours the fridges are still in the cruiser, maybe theres too much moisture or condensation coming from them , i dont know
I wont be happy if the thermistors on the fridges stuff up again, thats for sure, if they do i will be looking at a differant way to get the temp and fridge/freezer to work
I wonder what the genuin waeco thermistor is compared to Jaycar or others made
Regards Peter

DeBe · Guru

WAECO CDF-40 7.JPG WAECO CDF-40.JPG Your right the 2 transistors are NPN in the circuit ive drawn them wrong but down the bottom it says NPN 80v@700Ma.The thermistor resistor going to the7.3v rail is R1 30K.

dorian · Guru

Thanks very much for that. It's good to know that my memory hasn't yet failed me completely.

DeBe · Guru

the Jayco thermometer isn't available any more. But these are on Ebay for $2.50 to $5.00 freight free. I use several of them .

DeBe · Guru

This is the model being worked on in this thread CD-40 VERA. Quite diferent to the CDF-40. As it has a Micro processor controlling every thing. A calenge for some one to draw out the circuit of this one. Also the thermistor on this model must go in the position behind the compressor. Per the set of pictures. WAECO CD-40 AC VERA.JPG WAECO CD-40 AC VERA 2.JPG WAECO CD-40 AC VERA 6.JPG WAECO CD-40 AC VERA 7.JPG WAECO CD-40 AC VERA 8.JPG

-- Edited by DeBe on Tuesday 15th of April 2014 05:31:11 PM

possumyvonne · Senior Member

Daryl, just checked the temp on the fridge, i changed the setting to -8 and at the moment its on -2
Regards eter

possumyvonne · Senior Member

Daryl, i just got my good fridge out CF 40 VERB 6 yrs old
when i turned the fridge on ,i have the temp set to 4c , now that its been running the temp has gone up to 60c and when i change it to F the temp is -16
Any ideas on what could be the problem
Regards Peter

DeBe · Guru

The CF-40AC Ver b is diferent again. All the processor is up in the control panel, & is surface mount components. Rather difficult to repair , apart from replacing thermistor or push button switches. Are these the same control panel as yours? CP5 NTC on the board is where the thermistor plugs in, I would unplug it & check the resistance. An easy check is plug a good thermistor into the board & see if the temperature is more realistic. WAECO AC-40.9.jpg WAECO CF-40AC.10.jpg WAECO CF-40AC.11.jpg

-- Edited by DeBe on Tuesday 15th of April 2014 11:14:24 PM

-- Edited by DeBe on Tuesday 15th of April 2014 11:27:13 PM

-- Edited by DeBe on Tuesday 15th of April 2014 11:29:58 PM

dorian · Guru

If I were troubleshooting this problem, I would spend some time to retrieve the resistance-versus-temperature profile that must be stored in the microprocessor's memory. The way I would do this would be to connect a resistor decade box to the thermistor input (CP5), and then run the box through a range of 5K to 50K, say. It would probably be advisable to disconnect the compressor while performing these measurements.

Once you have these data, then choosing a suitable replacement for the original thermistor would be a lot easier. Moreover, by substituting known resistances, you could then quickly check whether the control board was behaving as expected at different temperatures. For example, if the set temperature is 4C, then you could select a resistance corresponding to 2C and check whether the compressor is switched off. Conversely, you could select a resistance corresponding to 6C and check whether the compressor is switched on.

Not sure how an end user would go about this, though.

possumyvonne · Senior Member

DeBe wrote:
The CF-40AC Ver b is diferent again. All the processor is up in the control panel, & is surface mount components. Rather difficult to repair , apart from replacing thermistor or push button switches. Are these the same control panel as yours? CP5 NTC on the board is where the thermistor plugs in, I would unplug it & check the resistance. An easy check is plug a good thermistor into the board & see if the temperature is more realistic.

-- Edited by DeBe on Tuesday 15th of April 2014 11:14:24 PM

-- Edited by DeBe on Tuesday 15th of April 2014 11:27:13 PM

-- Edited by DeBe on Tuesday 15th of April 2014 11:29:58 PM

yeah that the same as mine, the 35lt is still working in the cruiser, set at -6 but temp inside is -2

The 40lt ver b which is in the lounge is at 60c on display and continuously running, i checked the over ride and thats at normal. so have turned the fridge off

I dont have an other Thermistor to check as the 2 other ones i had here read 7.2ohms, 6.7ohms

Even the new one i bort only came to 9.3 ohms and that was straight out of the packet

Arnt they supose to be 10ohms new from waeco

Regards Peter

DeBe · Guru

They are 10K ohm at 25DegC any diferent temp they will read diferent, you only have to handle the body of them & you will change the reading. The Jaycar ones are pretty close to the orig thermistor. I suspect you have a faulty thermistor in the 40Liter one. Depending on the temp the 9.3K may well be ok.

possumyvonne · Senior Member

i will unplug the thermistor on the 40lt and tell you what the reading is, back in a minute

possumyvonne · Senior Member

hi daryl 10.92ohms
Regards Peter

possumyvonne · Senior Member

www.allvolts.com.au/index_page.html
This is the one i was telling you about, what do you recon
Regards Peter

http://www.allvolts.com.au/catalogue/cat/FRIDGE-FREEZER-COOLER-WAECO-SPARE-PARTS.html#catid=FRIDGE-FREEZER-COOLER-WAECO-SPARE-PARTS&carea=66&cpag=4&sqry=&sarea=&spag=

-- Edited by possumyvonne on Wednesday 16th of April 2014 10:15:27 AM

possumyvonne · Senior Member

just took a reading of the thermistor now 7.65 ohms, the inside is not cold and not warm to touch, just enough to take the chill off it
Regards Peter

DeBe · Guru

You may just have to take it to an agent, as nearly $100 for the board is a fair bit just to try.

possumyvonne · Senior Member

yeah thats what i was thinking
Regards Peter

dorian · Guru

.deleted

-- Edited by dorian on Thursday 17th of April 2014 06:14:47 AM

possumyvonne · Senior Member

possumyvonne wrote:
Daryl, just checked the temp on the fridge, i changed the setting to -8 and at the moment its on -2
Regards eter

Hi Daryl, just checked the 35lt fridge in the back of the cruiser, temp on display is -6 and inside fridge is 7c

Regards Peter

DeBe · Guru

So by putting the thermistor in the wrong position gives about 13Deg out in the reading.

possumyvonne · Senior Member

yeah, or some thing like that, cant understand why though, its still on the fridge and it all gets cold

dorian · Guru

If the display is showing "-6", whether Fahrenheit or Celsius, then the thermistor should be frosted over.

BTW, is it really "60C", or is it actually "60F"? And are the resistance really in units of ohms, or is it kilohms? And is the temperature "-16" or is it actually "16"?

dorian · Guru

Let's say we have a 10K thermistor when in fact the fridge is programmed with a resistance-temperature conversion table for a 5K thermistor.

If the actual temperature is 7C, then a 10K thermistor will have a resistance of 24195 ohms.

The fridge will then take this 24195 resistance measurement and convert it to a temperature that corresponds to a 5K thermistor.

A 5K thermistor will have a resistance of 24659 at -6C. That could explain why a 7C temperature is misinterpreted as -6C.

Here are the results of the Wikipedia equations:

10000 x e^(4100 x (1/(273.15 + 7) - 1/298.15)) = 24195

5000 x e^(4100 x (1/(273.15 - 6) - 1/298.15)) = 24659

possumyvonne · Senior Member

dorian wrote:
Let's say we have a 10K thermistor when in fact the fridge is programmed with a resistance-temperature conversion table for a 5K thermistor.

If the actual temperature is 7C, then a 10K thermistor will have a resistance of 24195 ohms.

The fridge will then take this 24195 resistance measurement and convert it to a temperature that corresponds to a 5K thermistor.

A 5K thermistor will have a resistance of 24659 at -6C. That could explain why a 7C temperature is misinterpreted as -6C.

Here are the results of the Wikipedia equations:

10000 x e^(4100 x (1/(273.15 + 7) - 1/298.15)) = 24195

5000 x e^(4100 x (1/(273.15 - 6) - 1/298.15)) = 24659

I just went out and checked the fridge temp, out side on display -11c inside cabinate 6c

And all i know is a brought the thermister which is a genuine waeco one for my 40lt ver b which is only 6yrs old, and i put the thermistor in the 35 ver a

There web site says 35lt to 50lt they are the same

im sure the thermistor is supose to be 10k @25 c

Regards Peter

ps is there a simple way to get the temp right

also should it make any differance where on the fridge the thermistor is put as long as its on the condersor

was also looking on the net and they say i should have used a special white glue to stick the thermistor on the fridge as i used aareldite

possumyvonne · Senior Member

it could also be the board thats not working properly, i recon it needs checking by a repairer
Regards Peter

DeBe · Guru

Yes it does make a diference where the thermistor is placed on the evaporator on the CF models with the digital read out. That's why its put in behind the compressor.