300SDL Always Hot? - PeachParts Mercedes-Benz Forum

JoeBobJr · #1 07-12-2010, 01:54 PM

I want to mention first that my fan control doesn't even work and I'm sure it's the cracked solder that is causing the issues on the climate control board. I plan on pulling it out soon and trying to rebuild it myself. Can't be much to remelting the solder and fixing all the bad connections.

I had to run a jumper hose from one side of the engine to the other to stop the heat from pouring into the inside of the car. Especially now that it's summer time. I would imagine that it's one of the pods bad that is closing off the hot side of the climate. If you guys believe that's the issue can you please explain to me which pod this could be so I can fix the one that is causing the issue. I wish I could just buy all the pods and replace them but right now money is tight I can't afford it. I just want to replace the one or two that is wrong and later on maybe I can do it again. I have no problem pulling the entire dash back apart if I have too.

whunter · #2 07-12-2010, 02:22 PM

The (electric) mono valve cuts off coolant flow through the heater.
The push button unit controls voltage: 12V = CLOSED and 0V = WIDE OPEN.

Here are the links you need to read for education on function/diagnosis/repair.

I suggest you Bookmark this master link for future need.
Fast navigation Do It Yourself Links
Fast navigation Do It Yourself Links

Climate Control:
Climate Control:

Monovalve Problems
http://www.peachparts.com/shopforum/tech-help/138522-monovalve-problems.html#post1026761

Mono Valve Voltages
Mono Valve Voltages

Mercedes-Benz A/C Control Diagnostics
http://www.peachparts.com/Wikka/AcDiags

Climate Control Repair
on the 1983 300D Turbo (W123 Chassis)
by BoostnBenz
2/16/04
http://www.peachparts.com/Wikka/W123ClimateControl

Have a great day

JoeBobJr · #3 07-12-2010, 04:16 PM

Thank you for all the guides I have a lot of reading to do. Is there one for removal of the climate control and radio and all that? I'm having hell trying to figure it out. I have the ashtray out that was easy to figure out. I pull the two GOLD screws off under the ashtray but for the life of me can't figure out how to get the radio out?

JoeBobJr · #4 07-12-2010, 05:21 PM

I finally got it all out I didn't realize that the stereo just slides straight out after that I found the screws that held everything else. I pulled the plastic cover off the climate control switch box and all the solder looks good I don't see any signs of bad connections on the solder itself like I have read is a common problem on these cars.

I am hoping it was just a bad connection on the harness itself that was plugged in I will make sure it's nice and secure and has a good connection before putting it all back together.

I wasn't getting anything at all from the switches though. The fuse is just fine but no matter what switch or what I set the speed on or if it's cold or hot I get no fan at all. It used to work once in a while and not work other times. Now it doesn't work at all.

Even though it doesn't look as if the solder has any bad connections do you guys suggest that I go ahead and remelt every connection and let it reconnect everything? I guess it wouldn't hurt to do it anyways.

ah-kay · #5 07-12-2010, 06:04 PM

IMHO, it is a bit a premature to pull the CCU. I would not do anything to the CCU yet as you have not found out what is the problem.

If I read your post correctly, you have 2 issues.

1) If the blower fan does not work, it could be the flat fuse. There is a fuse in a little black box outside the big fuse box. I once had a crack fuse and it was touching and breaking.

2) Are you getting heat but the compressor is working, i.e. the A/C hose is cold to touch but no cold air?

Good luck.

JoeBobJr · #6 07-12-2010, 06:50 PM

Quote:

Originally Posted by ah-kay

IMHO, it is a bit a premature to pull the CCU. I would not do anything to the CCU yet as you have not found out what is the problem.

If I read your post correctly, you have 2 issues.

1) If the blower fan does not work, it could be the flat fuse. There is a fuse in a little black box outside the big fuse box. I once had a crack fuse and it was touching and breaking.

2) Are you getting heat but the compressor is working, i.e. the A/C hose is cold to touch but no cold air?

Good luck.

I will check on that fuse in a few and see. The A/C does not work I think it's low on freon but I have never had the blower going long enough to even check the A/C. I get no blower at all. Whether the blower is on or not it always has hot air coming into the car through the vents. Off or blowing it's still hot all the time. I had to put a jumper hose from one side to the other to bypass the heater core because it was too hot inside the car. IT blows hot through ALL vents in the car. The heat never stops even with the blower is off.

JoeBobJr · #7 07-12-2010, 07:48 PM

I went ahead and reheated all the solder on every connection on the board for the climate control switch since I had it out. Figured it wouldn't hurt anything. I checked the square fuse and it looks like the fuse holder has been changed out to a heavier duty one. After pulling the top of the fuse holder I noticed the fuse was melted pretty bad but the actual holder was still in good shape no melting. I changed out the fuse and put everything back together and yet I still have no blower at all.

I do hear a light thonking noise coming from under the hood on the passenger side firewall. I would imagine it's the mono valve. I hear it making noises but I still have no blower at all. When I first got the car it used to work on and off. I'd be driving and all in a sudden it would come on and be working then later it would cut off and not work for days. Then it just stopped altogether. I found a fuse blown the first time it stopped working one of the straight fuses in the box. I replace it and it worked on and off again for a while but then it stopped and that fuse is still fine.

LUVMBDiesels · #8 07-12-2010, 08:39 PM

If I were you I would check that fuse again.They can look good but still not be. Does your transmission kick down work? That is on the same fuse.
If you have a volt meter, check the voltage at the monovalve. The valves do go bad and can leak. There is a replacement insert for them available from Phil.

As far as the blower goes, did you take the kick panel of from under the right side dash? Once you do, you can access the blower plenum and the fan. Try putting 12v right to the fan and see if it spins. I had a fan motor go bad. The melted blower fuse is not a good sign as it is 30 AMPs!

Good luck!

JoeBobJr · #9 07-12-2010, 08:43 PM

Quote:

Originally Posted by LUVMBDiesels

If I were you I would check that fuse again.They can look good but still not be. Does your transmission kick down work? That is on the same fuse.
If you have a volt meter, check the voltage at the monovalve. The valves do go bad and can leak. There is a replacement insert for them available from Phil.

As far as the blower goes, did you take the kick panel of from under the right side dash? Once you do, you can access the blower plenum and the fan. Try putting 12v right to the fan and see if it spins. I had a fan motor go bad. The melted blower fuse is not a good sign as it is 30 AMPs!

Good luck!

My transmission has never had a kick down good fuse or not. I didn't even know it had a kick down. Then again this is my first diesel so I wasn't sure if it was suppose to have a kick down or not. So no it doesn't kick down at all. If I really need the passing gear I just manually shift down to get the speed up faster. That fuse is still fine I already checked it I left it open when I put the new one in and turned the climate control defrost on and watched the fuse to make sure it didn't blow again. The fuse is just fine.

LUVMBDiesels · #10 07-12-2010, 09:11 PM

Quote:

Originally Posted by JoeBobJr

My transmission has never had a kick down good fuse or not. I didn't even know it had a kick down. Then again this is my first diesel so I wasn't sure if it was suppose to have a kick down or not. So no it doesn't kick down at all. If I really need the passing gear I just manually shift down to get the speed up faster. That fuse is still fine I already checked it I left it open when I put the new one in and turned the climate control defrost on and watched the fuse to make sure it didn't blow again. The fuse is just fine.

The kick down is activated by a switch under the accelerator pedal. The floor mats or carpet can keep the pedal from pressing it down. If it is being pressed and you have no kick down, I would suspect the electrics and that leads back to the fuse. Out the volt meter on it and see if it is still working. If it is, then you might have a wiring issue.

Another possibility could bee a seized auxiliary water pump. This is located near the monovalve and runs to circulate hot coolant through the heater core when you are at idle. If it goes bad, it could draw enough power through the CCU to burn it out. Since you did not see any burned traces when you had it apart I do not think this is the case.

When you push the CCU buttons do the pods cycle? You should be able to hear them opening and closing the flappers. If they do not cycle then I think you are not getting any power to the CCU. That is the black/red wire on pin 13 on connector X1

JoeBobJr · #11 07-12-2010, 09:15 PM

Ok so after looking closer in the fuse box I removed the two screws that hold the top of the fuse box down and lifted it up and noticed that the fuse for the blower motor had been taken off and spliced into an external fuse holder. The fuse inside that holder was almost melted in half. Which is not good being it's a 30 amp fuse. I have no clue why there is so many amps going through that wire to be melting a fuse like that. The fuse I replaced is just fine nothing wrong with it yet but I have no blower at all. I guess the next thing I do is check the blower itself to see if it cuts on after running a direct wire to it from the battery.

JoeBobJr · #12 07-12-2010, 09:21 PM

Quote:

Originally Posted by LUVMBDiesels

The kick down is activated by a switch under the accelerator pedal. The floor mats or carpet can keep the pedal from pressing it down. If it is being pressed and you have no kick down, I would suspect the electrics and that leads back to the fuse. Out the volt meter on it and see if it is still working. If it is, then you might have a wiring issue.

Another possibility could bee a seized auxiliary water pump. This is located near the monovalve and runs to circulate hot coolant through the heater core when you are at idle. If it goes bad, it could draw enough power through the CCU to burn it out. Since you did not see any burned traces when you had it apart I do not think this is the case.

When you push the CCU buttons do the pods cycle? You should be able to hear them opening and closing the flappers. If they do not cycle then I think you are not getting any power to the CCU. That is the black/red wire on pin 13 on connector X1

I tested the fuse holder and it's getting power my hot wire tester shows it getting juice. I don't hear anything from the pods when I click anything on the panel no matter what buttons I press. All I hear is that mono valve making noises over and over again. It never stops making noises. Even if I turn off with the last button with the 0 on it the valve still makes noises.

It sure is driving me crazy not knowing why it's not working. I have no defrost no nothing. Even though I haven't needed it for anything when I do I'm screwed.

Yak · #13 07-12-2010, 09:33 PM

Quote:

Originally Posted by JoeBobJr

Ok so after looking closer in the fuse box I removed the two screws that hold the top of the fuse box down and lifted it up and noticed that the fuse for the blower motor had been taken off and spliced into an external fuse holder. The fuse inside that holder was almost melted in half. Which is not good being it's a 30 amp fuse. I have no clue why there is so many amps going through that wire to be melting a fuse like that. The fuse I replaced is just fine nothing wrong with it yet but I have no blower at all. I guess the next thing I do is check the blower itself to see if it cuts on after running a direct wire to it from the battery.

That's a common mod. Assuming the external fuse holder has an M-B part number, it's a factory-approved "fuse saver". The blower motor can do a "slow burn" on fuses by continuously drawing high current, not enough to blow the fuse, but enough to heat the point of most resistance in the circuit - which is normally the fuse connections.

If your blower motor isn't turning and your fuse is melting, it may be seized. I'd pull the motor out and check for smooth operation, free spinning, etc.

JoeBobJr · #14 07-13-2010, 12:06 PM

Quote:

Originally Posted by Yak

That's a common mod. Assuming the external fuse holder has an M-B part number, it's a factory-approved "fuse saver". The blower motor can do a "slow burn" on fuses by continuously drawing high current, not enough to blow the fuse, but enough to heat the point of most resistance in the circuit - which is normally the fuse connections.

If your blower motor isn't turning and your fuse is melting, it may be seized. I'd pull the motor out and check for smooth operation, free spinning, etc.

Thanks Yak I will definitely check that out asap. That was my next step after seeing just about everything else I was starting to assume it was a blower motor problem. I will keep you guys updated on what I find out. Thanks for all the help.