A.C. Problem.. - PeachParts Mercedes-Benz Forum

McDiesel · #1 08-21-2004, 12:34 PM

1992 300 turbo diesel 2.5 5 cylinder...

the air conditioning yeseterday worked fine on the way to work..

when i went to lunch it worked fine ... 40* degrees on my thermometer in vent.. 95* outside..

on way back from lunch the ac would not engage...

on way home ac again was inoperable.. blower motor is fine.. I just replaced the orig one in spring of 04., no cold air.. freon level is where it should be

about 40 miles into my trip home i switched on the air and it WORKED GREAT AGAIN.. got home restatred and all was fine..

today i go out this am it worked fine drove 5 miles to get a hair cut..
came out HAD NO AIR COND ANAIN AND NOW ALL OF A SUDDEN THE TACHOMETER IS NOT WORKING..

any ideas?? LISTED BELOW THERE ARE SO MANY THINGS THAT CONTRIBUTE TO THE AC SYSTEM and of course its saturday the mechanic is off!!

mono valve ? to the touch after running it would fry an egg!
Coolant Temperature Sensor?
Coolant Temperature Sensor/Switch (For Computer)?
Cooling Fan Motor Relay?
Cooling Fan Resistor ?
Condenser Fan Resistor ?
expansion valve?
compressor clutch relay?
compressor control module?
Condenser Fan Motor Relay?
Evaporator Temperature Sensor/Switch?
Heater Core Temperature Sensor/Switch?
Pressure Sensor/Switch HVAC?
Cooling Fan Temperature Sensor/Switch?
Heater Control Valve?

Going to let the car sit all day and see if about 8pm tonight the damn air come on or not! then i suspect the Mono vale if it stops when car gets hot...

looks like im headed to the hvac woes!

McDiesel · #2 08-21-2004, 12:50 PM

why me! the thing that bothers me is now the tach is not working either...

will report back later after car cools off to re-check .. now i cant even look at the tacj to see the slight drop in rpm when compresser is engaged!

you can times that icon by a ga-zillion im so mad! :>

on another note I just purchased a 1977 jaguar xj6c coupe..

at least now i can drop off PROBLEM

car and still have wheels

to get around

#3 08-21-2004, 04:08 PM

Check the condition and tension of your serpentine belt. If it slips, there is a sensor on the compressor that kicks out the compressor. Turning off the ignition and restarting the engine resets it.

The next thing after that to check is to see that the temp sensor sample blower motor is running.

Good luck,

McDiesel · #4 08-21-2004, 04:48 PM

Just replaced belt shock tensioner, and pulley, new belt, and thermo viscus clutch, plus altenator less than 3 months ago..
Already had to replace the voltage regulator < less than 3 weeks after rebuilt one> No warranty on electical parts, hehe

But Im still Baffled on the Tachometer stopping at the same time..

I was reading the testing procedures on it.. just not in the mood to go under car today.. ... and not enough strenth to pull cluster out in this 95* heat and 100% humidity in Jersey...

larry how do I check that sample blower temp sensor motor.. < and where is it ? > im not as smart as look

your not talking about the sensor on the roof near the interior lights are you?

BTW I just replaced the blower motor less than 3 months ago due to the old one was shot...

my temp gage is reading its normal 80-90*C

McDiesel · #5 08-21-2004, 04:59 PM

the blower motor works fine.// low, high, and auto all turn the blower on and it is functioining properly

Thanks,,,,

BrierS · #6 08-21-2004, 05:42 PM

The "sample blower motor" attached on the right side just inside of where the glove box is. If yours is in the same place, you remove the glove box and should see (with a light) a hose similar to a garden hose attached to the sample blower motor. Following LB's advice I followed the hose, pulled the motor from its mount, removed the hose and was able to observe it working. The hose runs up to the sensor near the ceiling light you mentioned. Still following the advise, I inserted a hose within the one removed from the sample blower motor and blew on it to see if air flowed to the sensor. It did. I put a piece of tissue where the hose connects to the blower and it barely held the tissue in place (should hold it as it should up at the sensor).

If you have the KLIMA behind the battery SB mentioned searching for the Ice Cube relay bypass. I never had to go that far (yet) since switching the ICE Cube relays (under the cover behind the fuse cover) around and cleaning the KLIMA contacts and putting dielectric compound on them did the trick getting my compressor to run again. Wish I knew which of the many little things I did helped but I don't. I'll certainly follow your post.

Might I suggest that you get your hands on the Mercedes Service Manual Automatic Climate Control. I just received mine and have started preparing to go through their procedures. Between it and the posts here on the forum, I am going to be replacing all of the pods behind the dash. Lots of good posts on that.

Use the search and you should find four posts on here that have substantial details on these ticklish systems.

stevebfl · #7 08-21-2004, 06:14 PM

If you have no tach then you probably have no engine speed signal. If you have no engine speed signal to compare to the compressor speed, Klima shuts off the compressor.

The engine speed signal is made by the EGR transducer. The EGR transducer is powered by the OVP relay if I recall.

psfred · #8 08-21-2004, 09:58 PM

I second steve -- get a new OVP relay and install it. Should cure the rough idle, too.

Peter

fiero4819 · #9 08-22-2004, 05:07 PM

My AC and heat seem to work if I'm going down the highway and air is forced into the ducts due to highway speed. But the blower motor will not come on. I've removed the cover under the hood and when I connect it directly to the battery it spins fine. I've actually verified with an ohmmeter that the fuses are working OK. And since the two relays are the same in the fuse box, I swapped them. The blower still doesn't work but everything else in the car does. I also looked for obvious vacuum leaks under the hood and everything seems OK. The diaphragm modules I could reach hold their vacuum when I draw it. I then removed the center panel in the car and checked for voltage at the fan speed switch. I have no voltage whatsoever between any pair of pins. Where does this switch receive it's signal from? The wire bundle doesn't conect to the a/c panel but goes somewhere under the dash. What could cause the blower to not be coming on?

Thanks.

McDiesel · #10 08-23-2004, 12:24 AM

have you checked your strip fuse?

mine is in a seperate little cover... it looks sorta like this like |_|_____|_|

i believe they are 30 amp fuses... mine is located right above my drivers side strut under a black plastic cover with two copper leads going to it..

hope this helps'

pberku · #11 08-23-2004, 02:34 AM

Look at yesterday's (Sunday's) Diesel Forum. You will find a discussion called "A/C & Tach problems" The answer to your question is there.

Below is an extract.

The AC speed sensor, and the engine speed sensor both feed their signals to the KLIMA relay. The output of the two speed sensors is then compared and it if differs by more then approximatlery 10% the KLIMA relay shuts off the AC. The presumption being that the belt is slipping or that the AC compressor is seized.

The engine speed sensor also provides the input for your Tach. In your case it sounds like the engine speed sensor is not functioning properly, thus the Tach stops working and the KLIMA relay shuts off the AC as it sees different speeds at the engine and AC Compressor.

Fix your engine speed sensor and you should be OK.

Phil

McDiesel · #12 08-23-2004, 09:11 AM

thanks to all!!

my car is going in the shop today
to get the spped sensor fixed.. hoppefullly it will fix the ac prob!!

McDiesel · #13 08-24-2004, 09:24 PM

well the car is in the shop and im away on vacation.. but the mech quickly put the that senor that sends the reading to the tach and that was not it.. Still no tACH..

\

he is going to run a full diag on the thing from tranny sending crankshaft sensor OVP Kilma etc entire ac system from all those diff things AFTER he gets the TACH to work.. ugghh.. hope its not the Tach itself .. the instrument cluster is in there pretty loose from me replacing the dash bulbs recently, and i made sure not to snug it in tight like it was from the factory!

should be easy for him to get to the tach wiring..
i swapped relays except for my OVP because my 1990 is a different one from the 1992... really confusing to the Mech too he thought for sure that the speed senor would do it.. I know the kilma in there is ok and all of the fuses etc even the two on the ovp..

wish me luck and Im still open to suggestions!!

McD

FlyDad911 · #14 08-26-2004, 06:34 PM

If the engine speed sensor is not the problem, then the most likely cause is the voltage regulator. The secondary problem may be the output of the alternator itself. Is the ABS light coming on at the same time the tach drops offline? Then it's voltage from one cause or the other.

Hal

'87 300D Turbo (290k)
'83 911SC (106k)

McDiesel · #15 08-26-2004, 08:30 PM

Well thanks to all who replied!

it turned out to be a combination of 3 problems
1. r.p.m. sensor
2. a/c kilma relay
3. over voltage protection relay

i had to put an altenator in 3 weeks ago,,
then in less than 2 weeks had to replace the new voltage regulator in the altenator..
Mechanic told me that the ovp probably was shot when the first altenator fried...
which lead to the second voltage regulator getting fried too..

tokk 2 hours in labor @ 76 bux an hour = $152.00
plus the cost of the parts
$ 46 for rpm sensor
$ 120 for kilma
$70 for the ovp relay

now she works BETTER than Ever!!

cant be without AC here in Humid South jersey!!

thanks again to all!
McD