87 300TD AC Compressor won't go on... - PeachParts Mercedes-Benz Forum

Jay Gibbs · #1 08-09-2013, 07:53 PM

Another issue although hopefully it is easy...

AC was blowing cold until a couple days ago. Decided to degrease/wash engine. Shortly after wash, I noticed aux electric fan runs all the time whenever key is on- whether engine is hot or cold and AC compressor will not engage.

Took it to my local shop...they confirmed that the R134a is fully charged, and that the compressor runs fine and blows cold if they jump the power to it, but it is not getting electric otherwise. Thought it might be blown fan relay, but changed it (and compressor fuse) and still aux fan is on all the time and no compressor running. Anything else that can be quickly and easily checked? Supposed to be going away tomorrow for week vacation and not looking forward to the drive without AC!!

Any suggestions?

Thanks!

J.G.

ah-kay · #2 08-09-2013, 08:02 PM

Aux fan on slow or fast speed? If it is on fast speed then it is possible that the thermostat switch on top of the engine block is faulty or shorted. It is a 3-prongs switch which feed the Kilma relay with temperature info. You can try this

1) Remove the 2 prongs connector. The aux fan should stop. It is to turn on cooling when engine reaches 100C or 105C, depends on what part # is installed.
2) The single prong is the kilma input. Remove it and see whether the A/C comes on. It turns off A/C when it reaches 105C. This may be the problem.

Good luck.

Jay Gibbs · #3 08-09-2013, 08:22 PM

Quote:

Originally Posted by ah-kay

Aux fan on slow or fast speed? If it is on fast speed then it is possible that the thermostat switch on top of the engine block is faulty or shorted. It is a 3-prongs switch which feed the Kilma relay with temperature info. You can try this

1) Remove the 2 prongs connector. The aux fan should stop. It is to turn on cooling when engine reaches 100C or 105C, depends on what part # is installed.
2) The single prong is the kilma input. Remove it and see whether the A/C comes on. It turns off A/C when it reaches 105C. This may be the problem.

Good luck.

BINGO! I removed the 2 prong connector on top of the thermostat housing and the fan turned off. I then pulled the single pin connector (next to the two pin connector) and the compressor came to life!...ac is blowing cold. So I guess I need to replace this sensor with the 3 prongs? If I can't get it quickly, can I leave that one prong connector off so I can use the AC until the part comes in? Also- you wouldn't know the part number or the name of what this sensor is called so I can order it?

Thanks!!

J.G.

ah-kay · #4 08-09-2013, 11:15 PM

I am glad to be of service. The single prong one is for A/C so it can be left off. The 2 prong one is for engine over heat. If you watch the temperature often then both can be left off. Note the color of your old part and reference the part #.

Red: 006-545-42-24 (100/110)
Green: 006-545-45-24 (105/115)
Grey: 006-545-61-24 (105/120)
Blue: 006-545-64-24 (105/128)

I have a number of spare ones. PM me and I can send it to you for the cost of postage.

Jay Gibbs · #5 08-10-2013, 08:43 AM

Thanks- on many fronts, Ah-Kay...this was a great help. My wife will be thankful for not having to drive hundreds of miles this next week with no AC, and I am thankful for not having to listen to the endless complaints about the same! ; - )

Thanks for the offer...I found a company that has one in stock not far from where will be driving to on vacation. I'll pick one up there Monday and install it on the run!

Have a great weekend!

J.G.

Air&Road · #6 08-10-2013, 11:56 AM

What may very well have happened was the washing wet down the compressor clutch enough to let it slip on engagement tripping the rotational sensor circuit, then it dried out while you were doing the other things.

Glad it's fixed.

ah-kay · #7 08-10-2013, 12:03 PM

What a load of rubbish !! I wish poster would read prior posts FIRST before render their useless opinions.

Jay Gibbs · #8 08-12-2013, 03:36 PM

Quote:

Originally Posted by ah-kay

I am glad to be of service. The single prong one is for A/C so it can be left off. The 2 prong one is for engine over heat. If you watch the temperature often then both can be left off. Note the color of your old part and reference the part #.

Red: 006-545-42-24 (100/110)
Green: 006-545-45-24 (105/115)
Grey: 006-545-61-24 (105/120)
Blue: 006-545-64-24 (105/128)

I have a number of spare ones. PM me and I can send it to you for the cost of postage.

Question on the above sensors...doing a little research, I see my 300TD calls for the "blue" temp sensor. The grey one is listed for the 190D. The red and green ones are for gas cars. (I'm assuming the numbers in parentheses are temperatures...) If that is the case, it would seem the blue one would allow the temperature to run hotter than the others. Is there any benefit/detriment to running a grey or green sending unit to start the high fan speed at a lower temperature? I know the OM603's tend to run hot to begin with...?

J.G.

ah-kay · #9 08-12-2013, 04:32 PM

I offered you one at minimal costs and you do not take it. What can I say. The numbers mean, first one - temp to activate the aux fan high speed. 2nd one - temp to cut off A/C.

I use the RED type on my 300SDL which has the same engine as yours. It gives a better margin of error as the #14 is prone to overheat ( IMHO, the problem with # 14 head is overblown ) but it may or may not be necessary. It all depends on your comfort level.

Jay Gibbs · #10 08-12-2013, 08:33 PM

Quote:

Originally Posted by ah-kay

I offered you one at minimal costs and you do not take it. What can I say. The numbers mean, first one - temp to activate the aux fan high speed. 2nd one - temp to cut off A/C.

I use the RED type on my 300SDL which has the same engine as yours. It gives a better margin of error as the #14 is prone to overheat ( IMHO, the problem with # 14 head is overblown ) but it may or may not be necessary. It all depends on your comfort level.

Thanks for the offer...I appreciate it. I decided that since I have replaced so many parts with new ones already, I wanted to replace the sensor with a new one too. I also wanted to make sure there was no problem replacing with a lower temp sending unit. I know with older VW's, if you replace a thermoswitch with a lower temp one, you also need to change the thermostat to keep the system in synch and operating properly.

J.G.

ah-kay · #11 08-12-2013, 08:46 PM

Quote:

Originally Posted by Jay Gibbs

Thanks for the offer...I appreciate it. I decided that since I have replaced so many parts with new ones already, I wanted to replace the sensor with a new one too. I also wanted to make sure there was no problem replacing with a lower temp sending unit. I know with older VW's, if you replace a thermoswitch with a lower temp one, you also need to change the thermostat to keep the system in synch and operating properly.

J.G.

What makes you to think I am offering you an old/used unit? Don't get me wrong, I will help all members if I know the answer but I just want to put the record straight

. But I do not have new red one anyway if that is what you are going to use.

Good luck with your selection.