AC question on my 86 300SDL..... - PeachParts Mercedes-Benz Forum

Hip001 · #1 08-17-2009, 02:10 PM

Quote:

Originally Posted by tangofox007

If the air is fairly warm, it is possible that your monovalve has a bad electrical connection and is allowing coolant to flow to the heater core. If that happens, the heat will overwhelm the cooling capability of the a/c and you will get warm air, regardless how how well the a/c system is working. Since the temp is regulating by modulating the monovalve, attempts to regulate the temp will not be effective.

You might try clamping or plugging a heater hose.

Oh wow, Good Call Tangofox! I'll try that when I get home! Should this happen to make a difference, where is this "monovalve" to which you speak on 1986 300SDL?

Again I am not a mechanic or AC expert but your comment makes sense because the temp did not change when I adjusted the dial. Is this monovalve vacuum controlled cause the vents did not change either when I pushed the defrost button.

brandlj · #2 08-17-2009, 03:00 PM

The monovalve sits on the firewall inboard of the battery, next to the ABS computer. It is not Vacuum controlled, only electronically controlled. When you pressed the defrost button the vents did not change? That is pointing to a CCU ( climate control unit) fault. Something electrical may have happened with your car. Have you checked all of your fuses in the fusebox? Have you checked the 10Amp fuse on top of the OVP? That is the Over voltage protection unit which sits on the driver's side of the firewall next to the KLIMA relay. Do you have any dashboard lights on while you are driving, specifically the ABS light?

daw_two · #3 08-17-2009, 03:01 PM

Quote:

Originally Posted by Hip001

Oh wow, Good Call Tangofox! I'll try that when I get home! Should this happen to make a difference, where is this "monovalve" to which you speak on 1985 300SDL?

Again I am not a mechanic or AC expert but your comment makes sense because the temp did not change when I adjusted the dial. Is this monovalve vacuum controlled cause the vents did not change either when I pushed the defrost button.

EDIT --- I see brandlj and I were posting at the same time.

Now, Hip001, we all understand that you are not an AC expert, but I know you do not have a 1985 300SDL.

Your typo is forgiven.

The monovalve "rebuild" kit is easy to replace. I did it. If you are standing on the passenger side of your car next to the battery, the monovalve is toward the driver's side looking over the battery. If memory serves me correctly, you don't have to remove the entire valve (it's a boxy kind of looking thing with 2 rubber coolent hoses and an electrical connection). You can unplug the electrical connection and take the 2 screws (do NOT drop) out of the top. The thing "pops" open (is there a spring in there? I don't remember). Inspect the diaphram on the top of the brass looking shaft --- It probably has a tear in it. Coda's did.

Anyway. Remember how the thing fits together. Take the thing apart with all the parts lined up. I think the rebuild kit comes with a shaft and new diapharm on it. Put all the parts back together.

tangofox007 · #4 08-17-2009, 03:09 PM

Quote:

Originally Posted by daw_two

The monovalve "rebuild" kit is easy to replace. I did it. If you are standing on the passenger side of your car next to the battery, the monovalve is toward the driver's side looking over the battery. If memory serves me correctly, you don't have to remove the entire valve (it's a boxy kind of looking thing with 2 rubber coolent hoses and an electrical connection). You can unplug the electrical connection and take the 2 screws (do NOT drop) out of the top. The thing "pops" open (is there a spring in there? I don't remember). Inspect the diaphram on the top of the brass looking shaft --- It probably has a tear in it. Coda's did.

At this point, there is nothing that suggests that a monovalve repair kit is needed. A torn monovalve diaphragm does not typically cause the symptoms presented.

Hip001 · #5 08-17-2009, 03:27 PM

Quote:

Originally Posted by tangofox007

At this point, there is nothing that suggests that a monovalve repair kit is needed. A torn monovalve diaphragm does not typically cause the symptoms presented.

I'm not sure about the dash lights or the fuses. I will check them when I get home from work.

Daw_two, Just waiting on a slip to bust someones b@lls aren't ya! LOL! Good catch my friend!(I did the edit correction)

I will double check the fuses and the 10A on the OVP. and for grins double check the monovalve location/connections. If I understand correctly it is sounding more like electrical issues now.

Brandlj, There are no indicators on the dash showing anything different than normal.

Can someone tell me what "KLIMA" is?

brandlj · #6 08-17-2009, 03:55 PM

KLIMA is the relay that controls your A/C compressor. On our 300sdl's we have certain things that go through the KLIMA relay that lets the compressor know if it should be on or off.
1. Belt slippage on the A/C pulley. There is a RPM sensor that will shut off the compressor if the belt slips or if the belt falls off etc...
2. Wide open throttle microswitch. When the throttle is wide open, foot to the floor it actually touches a microswitch in the engine compartment that shuts off the compressor.
3. High temp switch. Once the engine reaches 105 degrees a temp sensor in the housing on the engine by the upper coolant hose sends a signal to the KLIMA to shut off the compressor and turn on the high speed electric fan in front of the condensor.
4. Pressure switch on the drier. If the pressure in the A/C system is too high or too low it sends a signal to the KLIMA to turn the compressor off or not to turn it on.

If there are any more that I have not touched on, please add them.

daw_two · #7 08-17-2009, 04:12 PM

Quote:

Originally Posted by brandlj

KLIMA is the relay that controls your A/C compressor. On our 300sdl's we have certain things that go through the KLIMA relay that lets the compressor know if it should be on or off.
1. Belt slippage on the A/C pulley. There is a RPM sensor that will shut off the compressor if the belt slips or if the belt falls off etc...
2. Wide open throttle microswitch. When the throttle is wide open, foot to the floor it actually touches a microswitch in the engine compartment that shuts off the compressor.
3. High temp switch. Once the engine reaches 105 degrees a temp sensor in the housing on the engine by the upper coolant hose sends a signal to the KLIMA to shut off the compressor and turn on the high speed electric fan in front of the condensor.
4. Pressure switch on the drier. If the pressure in the A/C system is too high or too low it sends a signal to the KLIMA to turn the compressor off or not to turn it on.

If there are any more that I have not touched on, please add them.

KLIMA probably stands for the first letters of a phrase in German that when translated means something like one of the following:

"The mother thing that must work for the AC to work"
"The queen mother component of the AC circuit"
"The ('B' word) --- why did those Engineers design this thing?"

Well, you get the idea. The engine lives by and the AC dies by the control under the KLIMA.

I just thought of something for Hip001 to check. I bet when he is not experiencing #1 in brandlj's post, he is experiencing #2.

No wonder his AC compressor isn't on.

Hip001 · #8 08-18-2009, 09:28 PM

ok, go figure this dam thing started working somewhat on the way to Pierre's shop. but something was still not right due to some of the air flowing out the defroster. Pierre is getting me some kind of actuator something to direct the flow better when we test drove it we smelled smoke

electrical smell. looked in the fuse box and the blower fuse was melting but not blown

, he said the blower resister or something like that was prob the issue.

daw_two · #9 08-17-2009, 04:06 PM

Quote:

Originally Posted by tangofox007

At this point, there is nothing that suggests that a monovalve repair kit is needed. A torn monovalve diaphragm does not typically cause the symptoms presented.

I concur --- I was merely suggesting to him how easy it is to replace the monovalve IF it were the issue.