air con control unit......

[paulmb]

Can anyone tell me where mine is.........1999 c200 sport?

is it under the passenger side dash or behind the heater control?

thanks

paul

 

[paulmb]

anyone???????????????

i've got a short somewhwere from the a/c control unit to the compressor.

thats why it comes on and cuts out.........i have found a wiring diagram of the layout and want to run a new wire from the unit to the compressor, by-passing the original.

however, the good news is that it worked a treat throughout the weekend and is still working. want to get everything ready for when it cuts out next.......just a matter of time.

 

[jasohal]

Paul, I would say that the control unit is behind the actual 'controls' on the centre console - this is what I found on my W124 E320 .

How do you know you have a short anyway ? The compressor also cuts out if there is less gas ( and hence pressure ) in the system or also too much pressure.

I would have the gas checked in the system before going down the wiring route personally...

 

[paulmb]

thanks jas.

there is plenty of gas in the system. Had it refilled after changing the coolant pressure swith on the dryer/receiver.

It has been checked by two a/c specialists who have confirmed that there is no leaks in the system.

when it cuts out, there is no power going to the compressor, however, when its running, it carries 3.15volts to the compressor.

definately a short or a damaged wire somewhere.

i'll try and take it apart on the weekend

how big is the a/c control unit?

 

[Glenn Smith]

according to my autodata CD it's located just below the heater control panel possibly somewhere near the radio, although the picture is not very detailed, I'll try to post the diagram.

 

[paulmb]

thnks mate...i found it...its attached to the fan speed controller on the back of the trim.............are these aircon control units a common problem?

 

[Glenn Smith]

Not especially I don't think, but like everything that works it can also break! Have you deduced that yours is faulty? Is it worth taking apart to see if it's a dry solder joint on the output to the compressor Pin 20 blue / green wire.

 

[Shude]

Not especially I don't think, but like everything that works it can also break! Have you deduced that yours is faulty? Is it worth taking apart to see if it's a dry solder joint on the output to the compressor Pin 20 blue / green wire.

The answer could be to swap with someone else who has the same car, see if it makes a difference

 

[paulmb]

HAVE TRIED ANOTHER UNIT GUYS.....STILL NOT WORKING.

How do i take apart the control unit without damaging it?

 

[Glenn Smith]

Check the voltage going to the unit, do you have digital climate or semi auto with the two temp. wheels?

 

[paulmb]

i have the semi auto with the two wheels........

what colour is the wire feeding power to the unit and what voltage should it be glenn?

where does this feed come from?

 

[Glenn Smith]

According to auto data there is three feeds ti unit, but doesn't show which one feeds the compresssor. I would check all of them.
red/yellow pin 1 from fuse 12
pink/green pin 22 from fuse 18
black and yellow pin 21 fuse 2

The black/yellow is interesting as it also feeds to the cooling fan relay, but doesn't feed the fans, it also feeds the in car temp sender and the recirc flap this means it has 2 joins somewhere. If these check out ok and you're sure it has a full charge of refrigerant try checking the continuity of the wires to the pressure switch on the receiver drier.
brown/yellow pin 3
red/white pin 14
blue/red pin 27

Have fun!!

 

[paulmb]

thanks glenn....going to try it out...will let you know

 

[paulmb]

funny you said that the black/yellow also feeds the fan relay....i take it thats the fan contol unit under the wheel arch?

i've had a new supply fitted to go to the fan control unit from the fuse box when the car overheated......apparently there was a break in the wire somewhere?!?!?!?!?

could this be linked?

 

[Glenn Smith]

Yep, thats the one, it has two supplies, one from fuse 29, 30amp for the fans, the other from fuse 2, 20amp. also some variation here depending on the number of cooling fans, my 230k has 2 electric and one viscous fan, I believe yours may have a diferent set up, looks like a likely candidate though.

 

[paulmb]

you seem like you know all about it.....fancy having a go at fixing it?!?!?!?!?!?!?!

i'll give it a go.hopefully, you have helped me out

cheers bud.

 

[paulmb]

mine has no viscous fan....only one fan behind the rad......same fan kicks in to cool the car and does the aircon.............

 

[paulmb]

so, my a/c started working itself?!?!?!?!?!?!?
have'nt even checked the wires that glenn mentioned........

but......2 hours later it cut out.......

so i pressed the EC and REST buttons down for 10 seconds and they flashed red then both lit up red and stayed red......

so i pressed the ec button to get rid of the light and hey presto......the a/c kicked in?!?!?!?!?!?

throughout the day it worked when the car was running. if i switched the car off and came back after a while, the a/c would not come on..........done the ec and rest button trick again....and the a/c would kick in......WEIRD

done this all day........

did notice my light behind the blower control where the a/c control unit is has been flickering for a few days........any connection to the problem?!?!?!?!?

disconnected the pressure switch on the receiver/dryer to see if this would do anything and put it back in.....now the a/c does'nt work at all....even after pressing the ec and rest buttons down..........

glenn.....where r u mate???????????need some help

 

[Glenn Smith]

Faulty wiring on the pressure switch? Also recirc flep is powered by same black/yellow that feeds cooling fan.

 

[paulmb]

do you think i should check the continuity on the three wires leading to the pressure switch?

what number fuse is the black/yellow wire connected to?

thanks glenn...........