Power steering fails when A/C is engaged
 

In low speed situations, when I'm backing out of a parking space the power steering will become very heavy and fail altogther if the A/C is engaged. What's going on here? Any ideas? Thanks in advance.

Is the belt for the AC and power steering shared? If so, maybe it's slipping quietly?

Sorry, it's a 1987 300E so yes, there is a serpentine belt. How tight should this be? Is there a reliable test?

Belt
 

1984 300d Turbo 140k
Replace Belt Diy 10 Min Work

I'm afraid you're right, I checked the belt this morning and it's quite loose. I checked for a tutorial on this site but it doesn't seem to have one for the 300E.

Can anyone give me a quick how-to on replacing the serpentine belt on a 1987 300E? Actually, maybe I should make a whole new thread title for this. Hmmm...

Click on URL below, then select -> 13 - belts. 2 service tasks listed.

Ignore the "300SEL" that you may see in URL. This car uses same motor/drive belt/etc as yours and the task you seek is not contained in the braingears 124 section. Duplicate info. Guy who setup braingears was likely trying to save server HD space.

http://mb.braingears.com/126_DISC1/program/engine_300SEL.htm

This is all I get...

Not Found

The requested URL /126_DISC1/program/Engine\103\13-342.pdf was not found on this server.

You could have a defective belt tensioner. Do a search for lots of info on this - common problem with this vehicle.

it works for me - can't say why it doesn't for you - sorry.

try -> http://mb.braingears.com

My experience is that the belt tensioner is pretty used after around 100k miles.

Definately the belt tensioner.