Need some quick advice - '78 300D
 

I am thinking of purchasing my second mercedes - a 1978 300D (I have driven a '72 250 for the past 3 years). The body is in great shape, little if any rust and the interior is OK - needs a good cleaning with a few tears here and there. The car runs fine and probably has over 300,000 miles on it (the odometer quit at 227000).

Here's what doesn't work - the blower motor doesn't work so I don't know about the H and AC, grinding noise coming from front right wheel when you turn the car to the right (wheel bearings??), sunroof motor operates, but grinds (sounds like it has come off/out of the track??).

I know nothing about diesels, so I really don't know what I'm getting into with this car - any advice? What should I check before I purchase??

BTW, price is $550. Thanks.

Ryan

priorities
 

First, raise the front right wheel off ground and see if there is excessive play in the wheel. If so, pull wheel, inspect bearings; if it's a bearing problem get new bearings and seal for that wheel and go from there to the next problem.

Climate controls on that car are operated by the ACC servo (large can with lots of wires and vacuum lines on right fender near front of engine). They fail and are expensive to replace ($400-900). Be aware of this problem and expense before deciding whether to purchase it. No worry if you don't need heat and/or AC.

I needed heat but no A/C right now, so a quick fix was to bypass the servo with coolant hose and couplers. Depends on whether you want A/C or not, as you get heat this way, but nothing else.

He's in Oklahoma. He WILL want AC....

Makes me want to find a cheap motor for my '77 parts car...... No rust, good suspension, good interior, bad chain.....:eek:

Yes, the blower is a significant issue. How do you know that it is this ACC servo and not just the blower motor? Can someone give me some TS tips - and if it is the ACC is this a part that I can purchase? What part am I looking for?

ryan

A visual inspection of the bottom of the servo might tell if it is cracked and/or leaking. That's a dead givaway. Performance Products sells a replacement system that is probably better than trying to replace the servo. Someone rebuilds them with a metal base instead of the plastic. Search on ACC servo here and their name/website should show up.
If you're getting heat/cool air by adjusting the system, it could be the brushes in the motor but the servo on these is a not uncommon problem.

I found this on the Performance Products web page : http://www.performanceproducts4benz.com/productpage.aspx?pid=100560&name=AC+Servo+(New)

$1675 ?? - Surely there are other options, aren't there? I have until tomorrow to decide about this car, but this is a major concern - and i really know nothing about this servo.

ryan

just check the AC climate control amplifier. it sits behind the glove box.
remove the GBox liner and look.
if it is burnt then relace it with a used(good) one. that will give you the heat and AC back.
assuming the visual inspection of klima servo is OK.

I have checked the ACC servo box and it LOOKS fine - no cracks and no evidence of any leaking at all. Someone mentioned checking an amplifier behind the glove box - how do I get to it w/o tearing things up (this isn't my car yet, so I want to be careful)?

Is there anything else to check?

Ryan

open the glove box. maybe remove the door. screws at hinges. the glove box liner inside is held in by screws inside. You may have to remove the latch
at the top also.

Then pull out the liner after you can tell that the retaining screws etc. are detatched.

the amp is about 2 or 3 inches long- rectangular.

brown or black if memory serves me.

pull off of its socket and inspect. I think I recall thAt tou can pry it's cover open. look for burnt scars or smells.

not the best instructions but memory is foggy. Once you are into it, it will make sense.:)

Is this the part you are talking about - jpg is attached?

If so, I can not find that part behind the glovebox. Are there instructions anywhere on troubleshooting this climate control system? I have no blower at all.

ryan

yup
 

Yes that is the part.

Performance products.com catalog #83-065 $112 climate control amplifier all models W123 to 1980 except 230, no turbos.
your 1978 300d has it. my 79 300d has it. same car.

keep looking , it may have to be reached for but access is gotten from behind glove box area.

Try using the archive search function. Look up blower etc. for tips.

When my amp went out, my blower worked but I had no hot air and the AC did not work.
once replaced with a good used one, the hot air came back and so did the AC !

Den

also do a search for w123 service manuals on this forum.

there is a web site like mbz gearheads that has service manuals online.
look up your car.