View Full Version : R134 up to spec, AC compressor working but not coming on.

06-30-2013, 09:53 PM
Had the freon level checked the other day and its fine and also compressor is good but not turning on.

Possibly a bad module or fuse, what steps would I take to test these things? Thanks in advance! It's a 06 Sprinter

The AC was working good but would sometimes take 20 min until it started to blow cold, now it had completely stopped working.

07-01-2013, 01:55 AM
If the system pressure is good, you can check to see if the signal to turn on the compressor by unplugging the single wire at the compressor. The wire should pull straight out, but you may need to loosen the fastener that holds the connector to the compressor. With the a/c control on, you should have 12V at the wire. If not, it may be the climate control module or the pressure transducer. My climate control for the a/c is showing signs of going out.

Here's an un-approved technique that works for me when my a/c does not engage (mine recently started acting up). Seems like a common failure among T1N's recently. If I give the climate control a good knuckle thump between the temperature sensor and the a/c switch, the a/c will kick in.

There's a very good description and guide in the service manual in the heating and cooling section. If you have access to a DAD or DRBIII, they will display the reading from the transducer and if the control module is sending a signal to the a/c clutch.


07-01-2013, 05:56 AM
Seems like a module or wiring issue because the guy who checked the freon ran a wire to the compressor and got it to work temporarily and when he disconnected his power source ac stopped working.

07-02-2013, 05:32 AM
The AC compressor relay which is soldered to the control module has bad set of load contacts ....I have seen this on a 04 and a 05 ...

07-02-2013, 10:01 PM
So can you just replace the Compressor relay or do you have to get a whole new 5103643aa control module? I've seen a guy on ebay who rebuilds them for around 100 bucks. If it doesn't fix the problem at lease you could get all your indicator lights working :dripsarcasm:

Rebuild mine for $89 or get a new one for $332, those are my options, is it something I could install myself?

07-04-2013, 08:42 PM
I soldered an external relay (with a zener diode) on the control module circuit to the 4 solder points ..still .working with 105 ambient temp

07-22-2013, 04:18 AM
I wanted to add that the clutch gap on the compressor was excessive and was over Charged with refrigerant ..which caused the contacts in the relay to fail

07-22-2013, 10:50 PM
That sounds similar to what is wrong with mine... what is the solution do you have to get a new compressor? Luckly mine has been cooperating and blowing cold air lately. I'm sure it will go into hot air limp mode again though :laughing:

07-23-2013, 10:33 PM
Thanks guys. I suspected that my heater control module was bad and this thread confirmed that it probably is. I need to replace it even if it isn't the problem because the heat control knob wasn't working and I had to remove it last year. Hopefully this will kill 2 birds with one stone.

10-09-2014, 11:36 PM
To MobileCC, do you have a picture of the relay on the control module? I do not see this relay referenced anywhere in the Sprinter docs, whereas I do see the relay on the relay block below the driver seat.

10-10-2014, 02:24 AM
Before doing anything!
Pull the control module and disconnect the passenger side socket.
Trace the single wire (black/green) :thinking: (off the top of my head) which is a direct feed to the compressor clutch.

With a power probe direct feed the clutch from the open socket side.
If it energizes then suspect the module /relay as discussed so far in this thread.

If you get no action then suspect the feed wire has a fault/high resistance in it and that is the direct cause!
Install a piggy back wire suggest #14 roll from a parts stockist and SOLDER & shrink wrap the thing in place of the redundant wire. Don't use crimp connectors you be doing it again soon!

Of these faults on A/C systems, I see about 60% are due to bad wiring continuity faults which is not at all uncommon on Sprinter T1N's & all MB C & E class products--CLK & Kompressor the worst :thumbdown:. Their wiring, harnesses and sockets are not the best compared with competition. But it pays the bills!:thumbup:
Toyota and Ford influenced LR instantly come to mind but Ford is the Zen master in that field --ISO 9000 certified and all that!
Oh field!! Circuits-- Wiring systems etc etc Excuse the pun! :bounce:
Cheers Dennis