87 300E climate control
 

My E has 296K miles but today decided to give me too much heat. The heat is constant and does not respond to changes in the dial thermostat. The heat comes out of the side vents but not in the center or down low. I am using the Economy button. Sometimes the fan keeps blowing after I hit the off button. Sometimes the fan speed buttons work, sometimes not. I can drive with a window open or leave the heat off. I checked the diaphram between the coolant near the battery and it did not seem to be torn. What is the best way to evaluate this?

lizem,
I would suggest removing the pushbutton control and resolidering all the connections on the bottom. the job only takes about 2 hours start to finish and it may save your wallet from the rediculous price of a new climate control computer.
Good luck!
Adam

Yes, indeed resoldering the CC unit MIGHT fix the problem. But you need to check the current draw of the auxilliary coolant pump that is located on the passenger side fender well. It should draw no more than 1.3 Amps. If it is drawing more than 1.3Amps, it probably knocked out an active component in the CC Unit. In this case, you should replace the pump and CC unit. If the cooling system is dirty, you might get lucky and be able to remove and clean and flush the pump and get the current draw below 1.3Amps saving that portion of the expense.

Good luck,

Also check the mono valve, when it fails, it is spring loaded to the open position and there is nothing to keep the hot coolant out.

Harry
86 300 SDL

i've read it somewhere that re-soldering the CC unit
must be done with care and knowledge of how the
unit works, since you may ground out other components
of the circuitry. hence, you need a new CC unit $$$$.

just a word of caution, good luck!!

Here is what I did and for now it works:

Finding a broken wire to the aspirator blower raised hope, but failed to fix
it.
Installing a mono-valve repair kit failed to fix it.
Re-soldering every connection (about 1100) on the two push-button circuit
boards did the trick.
I only saw one questionable connection, everything looked new, but there
must have been some.

My method was to cover the boards with strips of 3/4 inch scotch tape, then
remove one strip and work only that area. I inspected first and noted any
bridges that were suppose to be there, heated each connection for about two
seconds with a 25 watt iron. Inspected, cleaned and moved to the next
strip.

I also sprayed all switches and connections with Caig Lab's R5 contact
cleaner.

Before reinstalling, I replaced the aux heater pump with a 3/8" street el
and a 2' nipple. The pump bench tested OK, so it had not caused my problem.

The most difficult part was removing the engine heat shield, to be able to
get to the aux heater pump.

Thanks for all the tips posted on this list, I would not have even started
without the knowledge gained here.

Harry

86 300 SDL

thanks for the advice everyone.
I assume the cc unit comes out easily after removing the two screws holding the wood-just below cc and above the radio.
I will look for the aux coolant pump in AM.
will go to Radio Shack and get them to check the currant draw. Is the mono valve the one near the battery and held together by 4 screws?

Keep in mind that our MBs are different.

Yes, that is the mono valve and if you buy the repair kit, ($26) just mark for orientation purposes, remove those four screws and lift straight up. Note the order of everything, add the reusable parts to the new part and reassemble.

My aux pump was below the mono valve, it was hard to see and remove.

The CC unit removes as you said. I had to put a steady downward pressure to move it out from under the upper overlap.

I suggest you repair the mono valve and test the system, that may solve all your problems.

If you do the re-solder job, don't put your system to work until the aux pump is verified OK, otherwise, if it has failed, you may fry the CC, as Larry Bible indicated.

It was recommended somewhere, that an inline 2 amp fuse be installed in the aux pump wire to protect the CC. If I had left mine in service, I would have done so.

Good luck

Harry
86 300 SDL

The mono valve looks good-no tears. It is a diaphragm with a needle sticking up into another diaphragm. Should I replace it anyway?

I suggest you clean everything inside and out as best you can, then reinstall. Before you plug it in, test it with jumpers from the battery to make sure it clicks.

Button it up and try the system, if it works, hoorah, if not, only your time is lost.

Please keep us informed.

Harry
86 300 SDL

I have experienced the monovalve syndrome. Close inspection reveals no problems with the valves. But replacing them solves the problem. You cant really tell if they are defective by looking at them.

lizem,
You mentioned your pushbuttons will not function correctly right?
when you turn it off it stays on? I had the same problem and solved it by resolidering. although the aux pump seizing will fry your controller I would attempt this procedure you may be amazed. I would first try resolidering just the pushbutton switch connections not all 1100 points.
Good Luck,
Adam

Yes. I second Adam's suggestion that you resolder only the pushbutton switch terminals. They are pretty easy to find on the underside of the circuit board. Each switch has two rows of three terminals.

My primary problem symptoms were the fan running in the OFF position, and the AC compressor coming on in the OFF and ECONOMY positions.

The pushbuttons get a lot of stress normally, and a whole lot of stress from people who think violently pushing them in (while angry :mad: ) will somehow make the system act right. Once you get your pushbutton switch terminals resoldered - treat them very gently.

It is also worthwhile to resolder the three terminals that connect the round temperature setting dial if you can find them. They are in a row, adjacent to the wheel, on the circuit board.

By resoldering only switch terminals and the dial terminals, you avoid a lot of contact with more sensitive components that are probably still soldered in OK anyway. Its the control hardware terminals that get stressed and cold crack.

You may have other system issues, but this should fix the fan running in OFF.

Ken300D

Thank you all for your advice so far.
I checked the aux coolant pump. There were no obvious external terminals so I partially unplugged the male-female connector and checked the amps between the two prongs. It read 2.3 amps which is higher than 1.3 amps. Thus the aux coolant pump may be bad. I will double check the ammeter reading.
If the amp draw is really 2.3 and I checked it correctly by touching the leads to the plugs, then I assume I have to clean the pump(if lucky) or replace it.
Can I still try to solder the cc unit if the aux coolant pump failed or may fixing the aux pump fix the whole problem? Or does it mean the cc unit definitely need replacement and not just soldering?
Can I ignore the monovalve since I think we have found the problem?

Re advice on fan buttons. Sometimes the unit responds to speed requests sometimes not. Moving the thermostat dial makes no difference. I just get some heat and then shut the system off.

From your test description, I don't think you are familiar with checking current draw. To test current draw you must put the ammeter IN SERIES with the pump. If you did it this way and you indeed have 2.3 amps, the pump is definitely drawing too much current and probably caused CCU failure.

Good luck,

This Link Might Help
 

http://mechatronics.mech.northwestern.edu/mechatronics/design_ref/tools/multimeter.html

Current measurement section is at the bottom, but if you're not that familiar with a multimeter I'd suggest reading the whole thing.

If the connector to the auxiliary water pump is the typical two-wire plug-socket configuration, you will need to jumper one connection and measure in-series with the other. Typically, this means unplugging the connection, and jumpering what you determine to be the ground connection. This means it is effectively the same as if the connectors were plugged together.

Then, you use your multimeter in the current setting to complete the circuit between the two terminals that normally carry the battery supply (B+).

Hopefully they are obviously color coded. Fortunately, current is going to be the same whether you choose to measure the B+ line or the ground return line (if there is a ground return line). (So essentially, it is necessary to jumper one pair of terminals to their normally connected configuration, and measure in series with the other pair.)

You do not take a current measurement across the two terminals of the same connector. That is like taking the current measurement of the battery - very high current - will blow the meter's fuse or something in it.

Hope this helps,
Ken300D

You are correct that I DO NOT know how to check the current draw. I went to an Auto Zone and asked a counter man to help. He said he did not know too much either. We located the plug and separated the ends partway. I was not holding the ammeter but started the car. I came back and saw the reading 2.3. I was not astute enough at the time to see how he hooked it up. I also did not ask enough questions to satisfy myself that the machine was accurate and set correctly. I tried to test with another ammeter last PM and got no reading by a parallel method. Tonight I will pull the plug, twist it so only one male piece enters and complete the circuit with the leads.

If you put the ammeter in parallel, one of two senarios probably happened. 1) The climate control computer is fried, or 2) the ammeter is fried. Ammeters are always put in series with the load. Never parallel.

I went to a parts store and the counter guy could not give much info except he noted my aux pump had continuity. I went to Radio Shack and got an ammeter from them. In series I got .04 amps. The amps were + when one plug was bypassed and - when the other was. This does not seem to be much current. Is it low because the aux pump is toasted or because the cc unit is not asking for any. The cc unit just puts out hot air out of the side vents when on.

Earlier I did not get any current flow when I tested in parallel. Does this mean I did not toast the cc?

I checked my old records and in Nov 1991 my aux pump had trash in it and needed cleaning.

So- do I try soldering the cc, buy a new cc and aux pump or?

Ok a short lesson in electronics.

In your case, it sounds to me like you shorted the output of the climate control unit (hereafter refered to as the CCU) when you put the ammeter across the motor terminals. The ammeter has very low resistance and looks to the CCU as a short circuit. The motor normally draws about 1.5 amps at 12 volts so it has a resistance of about 8 ohms when it is running. But when you put the ammeter across the motor terminals (in parallel) the resistance seen by the CCU was almost zero which made the current go very high. This high current most certainly destroyed the switching element (normally a transistor) inside the CCU. Or it may have vaporized a PCB trace or both. Anyway, it is most likely that the CCU has been damaged. So now when you try to measure the current to the motor there is none because the CCU cannot supply any voltage since the circuits that do that have been destroyed.

I suspect that when you connected the ammeter across the motor terminals the first time, the needle on the meter would have jumped and pegged to the right for a very short time. You may not have noticed since it only takes miliseconds to destroy the circuit. If something fused open then there would be no current at all which is the case now. The current that you read now (40 millamps) is virtually nothing.

There is nothing that you could have done to hurt the motor. Either the motor is working properly or it is not. If the motor is not able to turn then it will draw a higher current than normal and put the CCU at risk. If you want to test the motor, unplug it from the CCU and then using clip leads connect it to the battery and see if it turns. If it does you are OK. If not it needs to be replaced. But the CCU needs professional help.

If you would like me to take a look at it, let me know. I have repaired several of them.

So do this;

1. Test the pump by applying 12 volts (proper polarity) and measure the running current. It should be about 1.3 amps. If it is significantly higher, replace the pump.

2. Replace or repair the CCU.

Make sure the pump is OK before you turn things on since it can destroy a good CCU.

Am I measuring correctly now?
 

After looking at Ken300Ds thread to see how to measure current, I measured current by plugging one male part into one female part of the aux coolant pump wire plugs. Then I touched one lead of the ammeter to the other male part and the other ammeter lead into the other female part. This is when I got .04 amps.

Before reading dpetryk comment I went back to the first store that originally measured 2.3 amps. The original guy was not there but another guy came out( I had to make sure the dial was set to amps and the leads were plugged in correctly...) to help me. He set up the measurement differently. He partially inserted both male parts of the connection in. Then he ran one ammeter lead to one male plug and another to a ground on the car. He got an amp reading of 2,4-2.6 amps. Is this the correct way to measure amps?

No. The meter must be in series with the motor leads. The ammeter must not be connected to ground. Ken's post assumes that you know which wire is going to ground. Which I suspect you dont. So the safe way is to put the meter in series with either lead of the motor and connect them to the original wires.

Thanks to all for the advice.

Dpetryk-I do not know which spade is ground on the plug as the wire away from the aux pump goes into a cover and I cannot visually trace it.

I am not sure where 1.3 amps came from. I called a someone with a shop manual and he said to put ccu in defrost mode and the reading should be less than 0.8 amps.

I will most likely take my car to a shop. I had climate control probs in Nov 1991 and the shop had much trouble figuring out the trouble. Will report what happens.

Ok I appreciate the report on what you find.

Today I looked at my old Suntune Dwell meter and noted it is really a multimeter. I will not have to borrow at Auto Zone/Radio Shack.. when it is dark.

The parts guy at a good shop who gave me the 0.8 amp defrost current draw info also told me the resistance on the mono valve should be 11-19 ohms. Mine tested at 15. I also got a super high amp load on the ccu-not sure if I trust it.

1.3 Amps is the MAXIMUM current that it can draw without blowing the CCU. If it is drawing anything MORE than that, replace it, or try flushing it and retest current draw. 1.4 Amps will blow the CCU.

Good luck,

what mechanic says about climate control
 

Took my 300E in today. Mechanics-two actually- first thought it was ccu. After replacing "all worked well until car hits some road bumps." Now they want to replace inside and outside temp sensors. If that works they will put the old ccu in to see if it was just temp sensors.

Lead mechanic feels new ccu better than rebuilt.

See also new thread on need for timing chain rails on 300Es with 296K miles. Should I replace the timing chain(first changed at 170K miles) while the over is off?

climate control saga continued
 

Got car back from mechanic. He felt monovalve and evaporator temp sensor were bad. Unfortunately problem not fixed. It does respond somewhat to temperatures now but no air comes out of the bottom/foot vents and sometimes comes out of the central ones-not supposed to happen in heat mode. Also temp regulation is too hot and tends to "hunt." I guess I will have to go back.

Mechanic also said "aux coolant pump just helps the car get heat sooner-not a big deal."

I may try to solder the ccu joints myself. How do I get the pushbuttons out? 2 screws and the wood is off. 2 more screws and the plastic mounting board comes off the dash. How do I get the pushbuttons out of the mounting board? Are there screws?

You have it right Lizem, to remove the buttons, just pop them out with a small screwdriver, you may need one on each side for the real tight ones.

Make sure you mark or note the orientation of everything you remove, because, some of these pieces (maybe all) have reflectors to carry light from the bulbs and your dash will end up dark. Don't ask me how I know this.

Harry
86 300 SDL

Lizem,
No need to remove the pushbuttons.... Just take the two screws out of the bottom of the wood cover. remove the cover. take out the two screws holding in the ccu. unplug the two connectors from the ccu. remove the "two" screws from the bottom of the ccu,, and your in..... Ahhh. i prefer to use a desolidering tool $9.00 at radio shack to remove the old solider. then take a regular old iron and fill in the blanks. Neatness counts! just try the pushbutton connections first. I was amazed how fast I was up and running.
Good Luck!
Adam

Adam, Harry, Larry, Dpetryk... I pulled the entire plastic unit out of the dash. Took off the top row of buttons(Rear deck light etc) and pulled the 2 electrical plugs out of the ccu. I took 4 small screws off the thin, plastic bottom plate. There exposed was a green circuit board. I could redo all of these solders but are there more? There seems to be another board deeper. Do I need to access it? How do I get the green one out? Do I have to pull the temperature wheel off to get both boards out? I do not see where the pushbuttons solders are now.

I did check the ccontinuity between the pins for the plugs and the green circuit board.

My local library has internet access to Mitchell's. Will they have good info. Does the MB shop manual have an effective algorithm to check all parts of the HVAC system? Is there any detailed source on line?

Many thanks to all.

Lizem,
You don't need access to the other board for this application. I've tried to remove the board in question and it's a pain in the a$$!
What I would do is just resolider the switches and temp pot in the box without removing anything else. Then I would plug it in and see what happens. BTW, if you suspect the aux pump i would take it apart and see if there is a problem. Only takes an hour at the most. Keep us posted!
Adam

I did use Mitchell's in the library. They had a very detailed algorithm to diagnose HVAC. I do not have 2 MB tester cables but it seems very logical. Touch certain pins and measure resistance to see if each part works. I will likely not buy the cables but I will ask the mechanic if he has them.

Final Report
 

Climate control works. Mechanic replaced the following

monovalve "saw water in the coils"
evaporator temp sensor(near accelerator) "circuit was open"
pushbutton unit -did not open doors and poor temp response
aux coolant pump apparently ran but current draw gradually increase to 10 while he was measuring. When we took apart the pump the bearings turned but not smoothly. The bearings had a notchy feel.

Amen. When the system works I do not notice it.

Congratulations Lizem, I am glad for you.

Many thanks for sharing your trials and tribulations with us.

Harry
86 300 SDL

Outstanding! Almost exactly the problem I have now. A/C will run in EC mode, will turn off when I press down and hold the EC button, kick back in as soon as I let off pressure. And half the time when I start the car, the blower motor will come on as soon as I put the key in Pos II to kick in the glow plugs, have to punch O to turn it off.

Already had the unit pulled out of the car, the bottom cover off, the temp dial removed, trying to figure out how to disassemble it further to get to the switches when I tumbled onto this thread. 3 AM so repairs will wait till tomorrow, but already sounds as if it's going to save me a lot of grief.

A few questions though -

This thread was originally talking about the CCU from an '87 300E. Same CCU in an '87 300DT?

Will a Radioshack ColdHeat soldering iron be adequate for this?

Would cleaning the circuit board and spraying it with a conformal coating after doing the resoldering be any help?

As far as the aux coolant pump - instead of having the pump powered off the CCU, would it be feasible to instead have the CCU powering a standard automotive 12V relay (using the wiring already installed to power the pump), with the pump powered thru the relay from another source (ie, straight off battery) with an applicable fuse in line?