odd series of events leading to no a/c today - PeachParts Mercedes-Benz Forum

1977busman · #1 08-13-2010, 06:49 PM

:EDIT: 1983 300SD :EDIT:

So Ive been driving this car for about 5 days now.
When we first got the car we charged the a/c, and it cooled OK but I have center vents.
So after running a vacuum line directly to the pod that opens the center vents it was "good to go" well the car never got cold, I would say 70 degrees at vent on average and occasionally 60 degrees (it been in the 90's with heat index above 100).
Well after driving some the car began to "hop" when stopped in gear, if car was put in neutral or park it stopped or if the a/c was off it would stop.

So heres how today went:

Put vice-grips on heater core hose to help with the vent temp issue.
Drove around till noon with an a/c system that was a lot better
Drove around with friend for the rest of the afternoon with the same old suckish a/c.
Noticed car hasn't "hopped" hardly at all, all day.
Also car running right under 100, instead of its normal 80 for most of day
Car blows number 10 fuse(25 amp), no aux fan,compressor, or blower fan
replace fuse two more times in 10 min intervals.
Finally gave up and waiting until it cools off tonight to check a/c charge

What else should I be looking for? Its fine for 5 days, and then bam fuse after fuse after fuse????
any guidance?

Diesel911 · #2 08-13-2010, 09:05 PM

Wich one of the cars;1992mercedes 300d or the
1983 mercedes 300sd?

What does the Fues Chart say the #10 fues is hooked to?

Yak · #3 08-13-2010, 10:03 PM

Your post is a bit hard to understand, but it sounds like at some points you're getting a significant vibration or "hop" when you have the A/C on?

Maybe your compressor is seizing and what you're felling is the belt jamming up or "surging"? I'd check your belts and pulleys. The higher temps may mean something going on with the water pump.

I don't know about the fuses. You'd have to check what's on that circuit.

vstech · #4 08-13-2010, 10:08 PM

yeah. can you describe "hop"
blowing fuse as in the element pops or the body of the fuse melts and it no longer makes contact?
the blower motors in the older mb's have a problem when the wear out, and the motor draws excessive amperage. not enough to pop the element in the fuse, but it's enough to melt the plastic around the fuse and the plastic fuse retainers. the solution is to one clean and shine all the contact points of the fuse retainer. also, you need to replace the fuses with CERAMIC copper fuses from this site, or your mercedes dealership. then you need to pull the blower motor and either lube the bearings, or replace the motor.

1977busman · #5 08-13-2010, 11:39 PM

its the 83 300sd, sorry for the unclearity

The "hop is a literal hop, like the car goes up and down, like im bouncing in my seat. the car rises about 3 inches, its like its going up and down in a surging motion.

The fuses are poping, the metal bands are spliting in half.

I dont have a fusse chart in my car, so I dont know what fuse 10 controls, but it seems like everything that shuts off when it blows is alot to be on one fuse.

Im just confused why for the last 5 days i have had no problems other than the surging(which i thought was vacuum related), to bam poping fuses.

Yak · #6 08-14-2010, 12:20 PM

Wouldn't it be great if there were a search function where you could find a "fuse chart"?

Fuse box chart, what fuse goes where

300SD 1985 Fuse chart

Fuse 10 appears to be the master fuse for just about everything A/C related and your water pump, so #10 blowing may affect temps.

But the "hop" as you describe it sounds weird. Literally "up and down" and not rocking side to side? A bad idle will cause the car to rock and you'll bounce up and down in your seat.

If it's as bad as you describe, you could be rocking something and shorting one of the things on the #10 fuse. I think someone just described where the kickdown switch on the tranny shorts out due to exposed wires: rocking + exposed wires on the circuit is an easy recipe for popped fuses. Or it could be a bad blower motor.

I'd get an assistant, pop the hood and stand to the side, have the assistant start the car and put it in gear at idle (just like you'd be a stop light) and you should observe what's going on with your belts and compressor. Smooth steady operation or jerky motion?

I'd still think you've got a seizing compressor or slipping belt that makes the engine rock. You may have bad motor mounts and shocks that makes it even worse.

pj67coll · #7 08-14-2010, 01:10 PM

If as you claim that hop only occurs with the A/C on which means the compressor engaged then it sounds like a bad compressor. I had a "similar" situation with my 72 Caddy back in 1993 when the rubber clutch on the compressor disintegrated. Bits of it fell out and caused the thing to go out of balance. When the A/C was engaged it seemed like I was firing a heavy machine gun. The whole car would literally jump up and down with the rate of rotation of the out of balance clutch assembly. Quite amazing that such a tank would be thrown out of whack by such a small piece of rubber but it happened. Not saying that this id definately what's happening in your case but it's worth checking out. Definately have someone look at the compressor etc with the engine running and the A/C both on and off. The situation with the fuses may be a different issue. Quite possible to have more than one issue at the same time with older cars.

- Peter.

1977busman · #8 08-14-2010, 10:53 PM

The car idles fine when a/c is off or in park or nuetral, so i dont think its an actual engines ability to idle issue.

The car does have completely shot shocks in the rear(push down on the trunk and she bounces a few times) so that could help but its still way to bad for it to be bad shocks.

Im going to check charge to make sure its not overcharged. And im going to watch the compressor and belts to see if its jerky and what not.

vstech · #9 08-15-2010, 09:10 AM

he was talking about the shocks on the engine mounts. if they are bad, lots of weird things occur with the engine vibrations.