Where is the A/C Relay on a 85 300TD? - PeachParts Mercedes-Benz Forum

paul300td · #1 06-27-2005, 10:06 PM

I am trouble shooting some ACC problems. Can someone please direct me to where the A/C Relay (5 pin) is located under the hood on a 85 300Td Wagon????

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1JX1BBNBK1JX1BBUFM&year=1985&make=MB&model=300-TDT-001&category=All&part=Relay

dannym · #2 06-28-2005, 08:43 AM

It should be in the fuse block.
In mine it's the front right relay. And the Aux fan is the front left.

If you think it's the relay swap them around. I found a bad one doing that.

Danny

sdparizona · #3 06-29-2005, 03:03 PM

I too am looking for this relay to trouble shoot a compressor that wont engage. in the fuse block on my 1985 300td there is only one relay and that goes to the aux fan. any ideas where else I could look??

dannym · #4 06-29-2005, 03:10 PM

Only one relay??
Are there spots where other relays can go?
If so try moving the relay around.
There should be one for the compressor and another for the electric defrost. There are probably more but they are the two that come to mind right now.

Danny

sdparizona · #5 06-29-2005, 04:09 PM

Thanks for the help danny,
My fuse block not only hase one fuse in it, it also has only the one place to plug it into. in the fuse block metal base all the mounts are empty fut the aux fan one, hmmmm
scott

paul300td · #6 07-01-2005, 03:09 PM

Mine is the same way - only one silver "ice cube". But I am looking for where this little guy goes....

http://img.eautopartscatalog.com/live/P202032107BOS.JPG

It is supposed to be a/c heater motor relay.

dmorrison · #7 07-01-2005, 03:20 PM

IAW the Service Manual you should have 2 ice cubes in the relay box just forward and to the left of the brake master cylinder. The diagram seems to show the erar one is the Ac relay. The forward one is the aux fan relay.

"Ac (code 12) and aux fan (code 6 ) relays."

Dave

sdparizona · #8 07-01-2005, 03:41 PM

Paul, it seems that in our '85 wagons the relay is not in the fuse block so it must be somewhere else. i'm really just boinkin' this thread to see if anyone else out there has any clue as to where it could be??

paul300td · #9 07-01-2005, 05:23 PM

Scott: This relay is ONLY used by 300 non turbos AND the 300TD Turbo. According to my research it appears as if it is near the blower motor under the dash on the passenger side, but still cant seem to find the blinking thing!

Fuzzball · #10 07-01-2005, 05:36 PM

Quote:

Originally Posted by sdparizona

I too am looking for this relay to trouble shoot a compressor that wont engage. in the fuse block on my 1985 300td there is only one relay and that goes to the aux fan. any ideas where else I could look??

Have you shorted across the pressure switch wires?

sdparizona · #11 07-01-2005, 09:06 PM

thanks for the thought, I am not getting any power to either side of the pressure switch. I know it is not the compressor. with the engine off I can contact directly to the compressor and the clutch engages fine. there is no juice to the pressure switch, and there is no juice to the etr valve under the dash. thinking there must be a problem with the ac relay if I can find it.....
Paul, I have my dash all apart right now trying to find it.... the glove box is out and there is no relay to be found so maybe it is under the drivers side.... anybody out there with any help?? sounds like both Paul and I have trouble shooted enough to need to know where this relay is....
thanks all
Scott

#12 07-02-2005, 09:00 AM

I can't help but wonder if some of you, except for SDarizona who is obviously on the right track, are looking for the relay before considering the bigger picture of this problem.

The most common cause of the compressor not kicking in is low refrigerant. There is a low pressure switch that interrupts the clutch circuit when pressure is low to save the compressor.

When you start a thread with such a specific question as where is the relay, you are losing the opportunity for help with the big picture. If you have already done the other steps to know that the relay is most likely your problem, then please state this.

I am not picking on anyone. I'm just trying to point out the best way to get help here. We want to help as best we can.

Good luck,

paul300td · #13 07-02-2005, 11:02 AM

Larry, et al.

As far as the big picture let me elaborate. My system has been been replaced as far as compressor, hoses, reciever/drier, evaporator core, etc. The unit works perfectly 90% of the time. When external temps get hot (and this could be a coincidence) about 10% ofhe time when I start the car and engage the ACC - NOTHING HAPPENS. No blower, NOTHING. I usually have to restart the car to get the ACC and blower to engage. all other time the A/C is ICE COLD, blower works fine, etc.

I replaced the ACC pushbutton controll, I have swapped out the ice cube relay under the hood, and now I am trying to locate the blowermotor relay to replace that one out. It appears as if the 300TD-T has a different configuration than the other other turbo diesels. I am planing on replacing a few more inexpensive relays as I trouble shoot. It seems logical that this five spade prong relay for the a/c blower might be the case. If anyone has an epc or knows where this little guy is (mine is a 85 300TD-T CALIFORNIA). Steve and I would be honored. PS: For a $10 part - we sure have spent a great deal of time trying to locate this part's location. : )

russb · #14 07-02-2005, 02:53 PM

Blower motor relay is behind the glove box, black, about 4" square. Up next to the windshield.
To the right of the silver climate control box.

#15 07-02-2005, 04:00 PM

Okay, now we're cookin'! As I said, knowing the overall problem can bring up some other possible solutions. On the 123 car a somewhat common problem that fits the scenario you describe is a flaky ignition switch.

The next time you start the car and the a/c doesn't work, wiggle the ignition switch and see if it comes on. I really would not expect a relay to work only 90% of the time although it is an electromechanical device so I suppose it is possible.

Thanks for backing up and giving us more background. Keep us posted.

Have a great day,

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