Dometic air conditioning fault help please (1 Viewer)

[Oscar]

The dometic b2200 roof a/c fitted to my van is not cooling,upon investigation I found the compressor is not starting. I have checked that there is power to the capacitor and compressor, and also checked both with ohm meter, and the readings all appear to be ok. Unfortunately I don't have micro farrad capability on my multi meters, so was unable to test capacitor using that method.

I have also checked the external thermostor located in the cooling coil, one time during my checks the compressor started & worked for 2 minutes before turning off, so I'm thinking it's possibly a control problem - anyone got any ideas or come across a similar problem?

I've been in touch with Dometic & they suggested taking it to a service agent. I took it to my local agent who was less than helpful - but that's another story to say the least!

Any suggestions?

Thanks

Alb

 

[Richard n Ann]

Where are you?
Does the compressor hum when trying to start?
When it ran did it switch off because it was supposed to? Or did it just give up

 

[Oscar]

Hi
We're near Scunthorpe in Lincolnshire, The compressor doesn't hum, when it ran it just gave up.
Thanks

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[Richard n Ann]

Is the neutral present? When there's correct power at the compressor but it doesn't run it will usually hum.
Is there a contactor on the system? If so check L&N in and out is correct.

 

[Oscar]

I've had the multi meter on the capacitor & compressor, these are showing 240v, and the current appears to be flowing through the compressor and back to the capacitor. When the compressor started, the multi meter showed a spike in the voltage at the capacitor, since then I've not had a voltage spike at the capacitor when I have turned the system on, I'm assuming that when I turn the system on there should be a spike in the voltage to start the motor turning, but there's no hum when on standby before I turn on even though power is present at the compressor.

 

[Richard n Ann]

On AC (usually) the capacitor is a permanent run capacitor. Start capacitors are on high starting torque refrigeration applications.

If everything is Live at the compressor, Neutral is missing.

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[Oscar]

So, what readings should I get from the wires to the compressor, there are 3 wires plus an extra earth to the compressor body

 

[Richard n Ann]

Using earth

C (common) should be live 240v

R (run) should be Neutral so should be around 6v

S (start) should read high, probably near to live voltage.


The run capacitor will be the only connection on the start winding and the other side will be connected to neutral

 

[Oscar]

Thanks, I'll get on the roof and check that

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[Richard n Ann]

Quick fag packet diagram ..

 

[Oscar]

Hi
I've been on the roof now, with the wires off the compressor in standby mode, I've got 245v on the Run wire, 0 on the blue start terminal wire, after the voltage is discharged from the capacitor and 0 on the pink wire which attaches to the common terminal via an overheat switch (voltage is flowing ok through this switch when active) I then tested them in run mode, still off the compressor - 245v on the run wire, 0 on the blue start wire and a small 10v spike on the pink common wire. I then connected the wires and all 3 terminals were showing 245 volts. I also found I was getting a 7v reading from the metal body of the capacitor, so I'm now wondering if the motor has ceased/stuck, I did notice when it started the other day the motor seemed to get hot quite quickly. I also re-tested the body of the motor to make sure that wasn't live, any thoughts would be appreciated.

 

[Richard n Ann]

The overheat switch (clixon) would be clicking if the compressor was seized up.

If you've got 245v on the run (neutral) you've lost the neutral and are measuring the live voltage through the compressor.

You need to trace the neutral wire away from the compressor, does it go onto a circuit board? Any burnt spade connectors or burnt tracks on the PCB. Does it go to a relay? Is it charred looking... These are all faults I've found in the past and fairly common.

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[Oscar]

I'm just going to have a look at this now. Cheers

 

[Oscar]

Update!
Checked all the wiring again, compressor was wired differently, as I said in my previous post I changed the wires around to see if it made any difference but it didn't. After that I inspected the circuit board, couldn't find any damage, so decided to check the continuity on the neutral feed, finding no continuity I decided to run a separate neutral to the compressor. This done, the compressor started to hum but wouldn't turn, so I re-instated the wiring to its original layout and tried again and it fired up straight away, cooling ok, so I've concluded that the fault is in the circuit board somewhere, which I have now removed and will attempt to diagnose - I've priced a new one (but would prefer not to buy one if I can help it) and it's about £350 with the postage from Leisureshop Direct.

Thanks for all your help and pointing me in the right direction with the neutral feed - I'll keep you posted on the outcome

 

[Just smiffy]

What an excellent help thread, just shows that we have all sorts of experience on here....

Good knowledge @Richard and Ann and good luck @Oscar ....

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[Richard n Ann]

Great news! You could always put an extra permanent neutral to the compressor if you don't get anywhere with the board