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KenT 07-28-2000 11:36 AM

Hello, I have a 91 300E in which the a/c stopped blowing cool air. Brought it to the MB dealership and they recharged the system and said they checked for leaks and saw none. It cost approx. $300. The air conditioner worked after that. The car was not used for 2 weeks or so after that and now the a/c doesn't work again. Brought it back to MB and now they did a flourscent dye test and said they found a slow leak in the compressor and that it would cost approx. $1600. I checked through partsshop that it would cost approx. $400 for a new compressor. Is this possible to as DIY fix? Could someone go through it step by step and suggest what other parts to replace or how I should go about all this? Thank you

ctaylor738 07-28-2000 05:45 PM

You are getting quoted $1600 by the dealer because of the approximately $1250 for the MB compressor and clutch.

If you buy the $400 rebuild you will need to change the oil if you are going to use R134. You will also need to remove the speed sensor and the manifold pipe fitting from the old compressor and re-install them on the new one. You will need new O-rings for these swaps.

You may wish to pay extra for a compressor that comes with these parts.

In any case, you will need the o-rings where the manifold pipe connects to the compressor.

I am not a professional mechanic, but the removal, parts swap, and reinstallation of the compressor was not too hard, although I did not get the sensor quite right.

You should then take the car to a competent shop to have the system evac'd and charged. Do not run the compressor in the meantime.

Jeffsr has a great recent post on how to loosen and remove the drive belt. Stevebfl has a lot of informative posts on this subject. Finally I would refer you to my own epic post "Cold AC but No Money."

Good luck.


jeffsr 07-28-2000 05:50 PM

Before you bite off a new compressor, find out exactly where it was leaking from. If it's at the rear at the manifold connection, then you may just need to reseal that component. Be sure about it before springing for the compressor..

Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE

KenT 07-29-2000 12:42 PM

Thank you for your help. I looked for drive belt removal post but couldn't find it could you give me a link. These are basic questions but am not familiar with AC repair. First, when people mention get the system evacuated can I assume that all the R-12 in my system is gone when their is a leak so this is the same as having the system evacuated? Can I change the compressor without the system being evacuated first? I saw in other posts that their is an another make compressor Ult.. not Nippondenso which is MB OEM which doesn't have as many points of leakage. Does this come with the speed sensor, manifold linkages? Finally about the oil. Is this oil inside the compressor, included with the compressor or do I have to get it changed somehow. I am planning on keeping it R-12 since it would still be cheaper than switching to R134 or I am right on this?

jeffsr 07-29-2000 04:09 PM

Here is the post on removal of belt..Enjoy

OK guys, here we go. For the 300E M103 motor, a number of things have to come off to do a decent job of either replacing or adjusting the tensioner or the belt. The fan shroud must be removed to have access. Two metal clips outboard of the clips that secure the radiator. Pull them off. Work the shroud up over the fan blades. Next, take off the fan blade. 4 metric allen type cap screws hold the fan to the fan clutch. Remove these. Then remove the fan, and shroud. Now you will have access to the tensioner retaining bolt. This is a big fella (19mm). Break it loose about 3-4 turns so it is not applying any pressure to the tensioner hub. Next, the tensioner adjusting screw. Located behind the power steering resevoir. Back this off 'till there is no tension on the belt. There is a little pointer with a scale in the tensioner hub. As you are relaxing the tension on the belt, the pointer should move to the right of the scale. When it reaches the end of the scale, you are OK. Now, remove the belt, making note of the path the belt takes around the pulleys. (it is possible to install it incorrectly). After the belt is off, you will have to remove the bolts from the power steering pump and lay that out of the way. There is a damper (looks like a little shock absorber) mounted on the tensioner hub. This is attached to the pad eye for hoisting the engine. Unbolt this from the pad eye. There is a bracket on the front of the tensioner which is attached to the engine behind the fan pully. Loosen this bolt enough to allow some movement of this bracket. Remove the big center bolt completely, hold the front bracket away from the tensioner hub and work the tensioner assembly out of the car. Reinstall is about the reverse of removal. Remember the little pointer!!. Remove this from the front of the tensioner and place it on the front of the new part. This pointer is adjustable and used to set the tension. Transfer the damper shock to the new tensioner. After installing the new part and replacing all of the hardware you had previously removed, with the exception of the fan and shroud. Put on a NEW belt, properly routing it about all of the pulleys. Do not tighten the big center bolt until you have set the tension. Set the little pointer to the far right end of the scale by gently pushing down on it and moving it a few notches to the right. When the pointer is set, begin taking up on the long tensioner adjusting bolt (behind the power steering resevoir), keep adjusting until the pointer reaches the other end of the scale. Tighten down the big center bolt, reinstall the fan and shroud and go to the corner and buy yourself a big cold frosty. Oh BTW, don't forget to close the hood after you're done...

Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE

ctaylor738 07-30-2000 08:57 PM

The $463 rebuilt Behr from Partsshop came with R12-compatible oil installed so you would not have to drain and refill it.

If you are sure that there is no refrigerant in the system, then you do not need to evac before removing the compressor.

Jeff has an excellent point--the leak may well be between the manifold pipe and the compressor manifold pipe fitting (2 o-rings), or between the compressor and the manifold pipe fitting (4 o-rings), or the speed sensor (1 seal). Mine was leaking at the first place.

If you pull the spray shield off and look closely at the compressor, you may be able to see the dye.

This is not oil-change DIY stuff. From the questions that you're asking, you may wish to locate a good shop - there is a forum on this site that lists them.


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