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Registered
1991 500SL
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49 Posts
Discussion Starter #1
I've had lots of issues with this car, EGR switch over valve had a vacuum line crossed with the one that goes to the switch over valve for the air pump the car started and run perfect BUT on the third time out my battery light came on so I tested the battery [Bad] tested the alternator [Bad] replaced both along with a new belt tensioner Now my Tech bounces like crazy the car surges and sometimes dies upon deceleration at all speeds ....eek! Please help and thanks in advance.
 

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Greek God of the R129
SL500-500SEL-190E
Joined
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8,530 Posts
You have a vacuum leak.
Disconnect and cap, the line that feeds the two switchover valves.
See if it helps.
Regards,
aam.
 

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Registered
1991 500SL
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49 Posts
Discussion Starter #3
Thanks aam I don't have a vacuum leak, Started the engine after checking and noticed when I turned off the A/C and turned back on the tack and Idle shot up to 2000 rpm, I unplugged and plugged in the wires that go to the air pump and the Issue seems to have gone away, I just replaced the alternator and battery so I checked voltage at the battery 12.6 engine off 14.3 engine on. I will drive the car today and see if its ok. Thoughts?
 

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Registered
1991 500SL
Joined
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49 Posts
Discussion Starter #4
You have a vacuum leak.
Disconnect and cap, the line that feeds the two switchover valves.
See if it helps.
Regards,
aam.
Hello aam I don't have a vacuum leak, Here is what is happening.....I drove the car to town town today [15 miles] On the way the tach started to bounce I turned the heater off and all was prefect! I turn heater on tach jumps to 2000+ rpm and engine sometimes dies when this happens until the engine is completely warmed up than all is great, This didn't happen until I replaced the alternator and battery. Engine off 12.6 V engine running 14.3 V
 

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Greek God of the R129
SL500-500SEL-190E
Joined
·
8,530 Posts
Hahaha,
So you want me to explain.
Most likely you have more than one problem.
The switchover valves.
One goes to the EGR. activates when engine is hot.
The other goes to the air pump. activates when engine is cold and only for a few seconds.

One line goes to the air diverter control. (about 6" away, from the switchover valves in the computer coffin.
This diverter control, controls the heater. ( Usually breaks at the bearing its plastic.)

In trunk air pump for the lock/unlock, goes in to this diverter, has about 6 vacuum lines ,from the diverter, an other line goes under the dash, over the passenger air bag, this is for the heat, is a distribution block, about 5 vacuum lines....

Back again to the diverter there is a line that goes to the air reservoir, located in the passenger fender. from this reservoir another line goes to the engine vacuum....
Somewhere in there is the vacuum leak.

Now electrical.
Engine computer, gets a signal from the a/c compressor speed sensor, raises the Tack RPM.
It also gets a signal from the four pin round sensor, located in front of the fuel distributor.
two pins are for the A/C. the other pins talk to the ECU.

Replace all the old vacuum lines and rubber fittings, autohause has good prices
You need about 25 feet of vacuum line and many rubber connectors.
For info. look at the radiator support diagram sticker.

Regards,
aam.
 

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Registered
1991 500SL
Joined
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49 Posts
Discussion Starter #6
Hello aam, No vacuum leaks, what I did find is no freon in A/C I read codes 14-11 and 12, 11- A/C compressor engagement signal missing and 12- Output for A/C compressor control defective. I filled the freon but the compressor works intermittently so I can't get it all the way full, but the tach does not bounce anymore [I think] and it runs better. Can you help me with this issue? Maybe someday I will get to enjoy this car!
 

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Greek God of the R129
SL500-500SEL-190E
Joined
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8,530 Posts
I need more info.
how did you charge the 134 refrigerant?
Did you vacuum, do you have an A/C manifold?

Any ways.
On the drier are two pressure sensors, one is green or red, with two wire pigtails.
The Green is for 134, the Red is for r12 If you have to replace get the Red, as the fan will start SOONER. Bridge the connector. the fan should constantly run.
Do not remove the sensors, as the refrigerant will leak out.

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Located on Receiver Drier for Auxiliary Cooling Fan, Identified by 2 Spade Terminals on Short Pigtail with Green Base





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The other sensor controls the refrigerant pressure. Over pressure, or Low pressure compressor turns OFF. If you bridge this one, you can add more refrigerant.

Am giving you info.
This job is for professionals.

On the front is the clutch, make sure that the wires have power. On the rear of the compressor, is the speed sensor,
If you have to replace one or the other, get a new compressor.
Rockauto,com has the best price for a new compressor.

Regards,
aam.
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Registered
1991 500SL
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49 Posts
Discussion Starter #8
I added 134 from a can with a pressure gauge I will bring it to my brothers house this weekend he is a A/C specialist for Caterpillar, The A/C was switched from R12 to R134 before I bought the car. As always Thank you, I will let you know what happens.
 

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Registered
1991 500SL
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49 Posts
Discussion Starter #9
Hello aam, I brought the car to my brothers he vacuumed and dried the system but could not properly fill it back up do to sporadic compressor turning on and off even with jumping the presser sensors, My next step is to replace compressor both sensors and receiver..........Then I'm going to burning this huge pain in my ass to the ground!......I'll keep you posted.
 

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Greek God of the R129
SL500-500SEL-190E
Joined
·
8,530 Posts
Burn the MF, Mercedes?
Blasphemy.
There are times, I feel the same.... Lol.

Before you change the compressor.
Try to hook a 12v line, direct, to the compressor clutch.
Bypass the connector, I don't want you to burn the ECU....That means, NO FEED BACK.
You got a brother in the trade?
Man, you are miles ahead...
You don't need me.
Good luck.

Regards,
aam.
 

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Greek God of the R129
SL500-500SEL-190E
Joined
·
8,530 Posts
I forgot you may have to replace the condenser/ Easy.
Expansion valve /Pain in the a&^.
A must, if the refrigerant 12 to 134 is converted. For 134 you need a larger condenser...
Get a RED sensor.
Make sure that they will screw in the new accumulator.
Regards,
aam.
 

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Registered
1991 500SL
Joined
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49 Posts
Discussion Starter #12
Burn the MF, Mercedes?
Blasphemy.
There are times, I feel the same.... Lol.

Before you change the compressor.
Try to hook a 12v line, direct, to the compressor clutch.
Bypass the connector, I don't want you to burn the ECU....That means, NO FEED BACK.
You got a brother in the trade?
Man, you are miles ahead...
You don't need me.
Good luck.

Regards,
aam.
I do need you Albert you and Bob are my heroes, It would be nice someday to meet you guys and enjoy a cold drink together!
 

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Registered
1991 500SL
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49 Posts
Discussion Starter #13
I do need you Albert you and Bob are my heroes, It would be nice someday to meet you guys and enjoy a cold drink together!
Happy New Year Albert, My compressor turns on and off on and off even when I install jumper wire, do you think I need to replace compressor, drier, condenser, and expansion valve? If so how do I remove the drier and where is the expansion valve? Also I replaced the outside temperature light it works fine but now my odometer doesn't work I did not add solder I just heated the solder and replaced the light, I made sure I didn't bridge any solder! UGH what next?
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,530 Posts
Happy New Year Albert, My compressor turns on and off on and off even when I install jumper wire, do you think I need to replace compressor, drier, condenser, and expansion valve? If so how do I remove the drier and where is the expansion valve? Also I replaced the outside temperature light it works fine but now my odometer doesn't work I did not add solder I just heated the solder and replaced the light, I made sure I didn't bridge any solder! UGH what next?
Happy new year to you too.

TXV is next & under to the brake booster, follow the a/c line, to replace space tight.
Have to remove the cabin filter, filter box, you will find that you have a windshield heater, heater air box heater,( helps with odors,) you have to disconnect 10mm coolant lines.
Coolant hoses have 10 mm branches engine to heater core, try not to damage as they are $100x2 each you will discover things you never thought...

Compressor turns on and off on?
Hmmmm.
Speed sensor, short wire, over/under refrigerant pressures, stuck worn out clutch, fillings from damaged compressor, blocking the system?
As you can see there are a lot of ifs.

Temp. light, odometer out?

One thing at a time?

Regards,
aam.
 

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Registered
1991 500SL
Joined
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49 Posts
Discussion Starter #15
Happy new year to you too.

TXV is next & under to the brake booster, follow the a/c line, to replace space tight.
Have to remove the cabin filter, filter box, you will find that you have a windshield heater, heater air box heater,( helps with odors,) you have to disconnect 10mm coolant lines.
Coolant hoses have 10 mm branches engine to heater core, try not to damage as they are $100x2 each you will discover things you never thought...

Compressor turns on and off on?
Hmmmm.
Speed sensor, short wire, over/under refrigerant pressures, stuck worn out clutch, fillings from damaged compressor, blocking the system?
As you can see there are a lot of ifs.

Temp. light, odometer out?

One thing at a time?

Regards,
aam.
Hello Alert, Well If I'm understanding your last reply I think I'll replace all the A/C parts, You mentioned a bigger condenser do you have a part# or are there options when I do my parts search? will I have to modify anything to get a bigger condenser in place? and do I remove the ASR pump to remove the receiver? so four parts, [1] Condenser [2] Compressor [3] receiver and [4] the valve under the cabin air filter, Is there anything else that I should replace while I have everything apart. Thanks again Alert don't forget about the odometer issue I hope that will be easy!
 

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Greek God of the R129
SL500-500SEL-190E
Joined
·
8,530 Posts
raockauto.....
NEW compressor. Most condensers are for 134A. List is complete.
The rest is up to you
Alert don't forget about the odometer issue Ihope that will be easy!

Here B, where is the B?
I forgot,
It's nice to be young.
Lol.

Regards,
aam.

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One of our most popular parts


R134A; OE-specified O-Rings Included; Unit Pre-Oiled


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without dryer (Only 1 Remaining)





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$337.79




Part image
$186.99 $0.00 $186.99
 

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Registered
1991 500SL
Joined
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49 Posts
Discussion Starter #17
raockauto.....
NEW compressor. Most condensers are for 134A. List is complete.
The rest is up to you
Alert don't forget about the odometer issue Ihope that will be easy!

Here B, where is the B?
I forgot,
It's nice to be young.
Lol.

Regards,
aam.

DENSO 4711227 {Click Info Button for Alternate/OEM Part Numbers} Info
One of our most popular parts


R134A; OE-specified O-Rings Included; Unit Pre-Oiled


MAHLE / CLEVITE AC210000P {Click Info Button for Alternate/OEM Part Numbers} Behr; Does Not Include Drier Info

without dryer (Only 1 Remaining)




<
Part image
>
$337.79



Part image
$186.99 $0.00 $186.99
So sorry Albert I'm tired I'm not young by any means and looking for some knowledgeable help, Thank you once again! So a young kid rides his moped by my house all the time, 1well last week he stopped and asked why the hood is always up on my car!!!!!!!!!!!!!!!!!!!!!
 

·
Greek God of the R129
SL500-500SEL-190E
Joined
·
8,530 Posts
Getting up,
take inventory, legs, blood pressure, shoulders?
If you don't understand....
You are still young.
Regards,
aam.
 

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Registered
1991 500SL
Joined
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49 Posts
Discussion Starter #19
Getting up,
take inventory, legs, blood pressure, shoulders?
If you don't understand....
You are still young.
Regards,
aam.
Hello Albert, Yes I check limbs and Blood pressure every morning! I had a heart attack and double bypass 15 mounts ago! Soooo I took my car back to my brothers house so he could evacuate the R134 I told him after the first attempt in filling the A/C system I cleared the codes and that's when the compressor cycled on and off......Soooo he told me if I wanted to clear the codes we could try again of course I said hell yes! I worded perfect It did not cycle on and off every except when it was suppose to temperature at the vent was 41.3 degrees we let it run for about 45 minutes.....prefect so I thought! half way home the tach started to bounce again, soooo could it be the MAF I read on other posts something about a KLIMA relay witch from what I have read my car doesn't have one but maybe the MAF relay, I just don't want to replace all the A/C components and have the same issue. I appreciate all your help and patients. I which there was a repair shop around here that was worth a shit! Have you ever considered moving to southern Missouri? LOL
 

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Greek God of the R129
SL500-500SEL-190E
Joined
·
8,530 Posts
I'm glad that you are doing well, keep it up.
OK, A/C is done, ice cold.
You don't have a MAF. You have a MAS module.
Bouncing RPM?
You have to be more specific, gauge is bouncing.
Or,
engine rpm going up/down?
Regards,
aam.

No Missouri, no divorce...











 
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