Hi does anyone have a circuit diagram on this dometic controller MFC20ad
not working on 12/24volt ok on 240volt...

 

Welcome to AAC, and I appreciate that you understand already that mot everybody has instant access to all information.
And now, based on information in your post, that device, a Dometic MFC20ad, is a controller, possibly a motor speed controller, normally intended to operate on 240 volts AC, probably 50 Hz, Probably it was not ever intended to operate with a much lower voltage. That is common, because ir costs less to only design a device for the anticipated operation voltage.
That is what I can tell you based on absolutely no other information.

 

@jimmy1570 The unit shows a supply range of 100vac-240vac,
Do you mean the LV DC is not operating when powered by 100v supply?

 

To clarify for the above responses. It is a dual supply controller, it works on both 100-240Vac and 12-24Vdc. It is a controller for car fridges. I have the same unit as you Jimmy and it works on 230Vac but when I plug it into the car @12V I get an intermittently flashing power light and the temperature started rising from the precooled level it was on from running on 230V. I am yet to pull the unit apart as I thought I had found a replacement for $100, which seemed easier than trying to fix my existing unit.
I am going to pull it apart sometime this week as the replacement unit hasn't turned up. I will let you know what I discover. Also, if you have found the cause/solution I would be interested to know.

 

To clarify for the above responses. It is a dual supply controller, it works on both 100-240Vac and 12-24Vdc. It is a controller for car fridges. I have the same unit as you Jimmy and it works on 230Vac but when I plug it into the car @12V I get an intermittently flashing power light and the temperature started rising from the precooled level it was on from running on 230V. I am yet to pull the unit apart as I thought I had found a replacement for $100, which seemed easier than trying to fix my existing unit.
I am going to pull it apart sometime this week as the replacement unit hasn't turned up. I will let you know what I discover. Also, if you have found the cause/solution I would be interested to know.

Trent12, wondering if you ended up pulling it apart, I'm having the same issue with my unit and trying to troubleshoot.

Thanks so much!

 

Have you checkd the voltage applied to the cooling element when using 12 volts supply?? For starters, it will require at least 10X the AC input current to deliver the same cooling. A voltage check will reveal a lot.

 

Trent12, wondering if you ended up pulling it apart, I'm having the same issue with my unit and trying to troubleshoot.

Thanks so much!

Hey,
So in the end I did pull it apart. There is a DC-DC converter at the end near the pins covered in silicon. When it was on 240Vac the output floated up to 24Vdc and the unit was able to run, when it was on 12Vdc it dropped to 7V under load and the control unit would drop out.
My solution was to buy another DC-DC for about $20 and I took the 24V DC from the input bypassed the output wire. I had some photos but I can't find them and tell you the exact colours. It seems to work ok now but I haven't tested if it still has low voltage drop out.