Climate Control System Died Suddenly - PeachParts Mercedes-Benz Forum

backstage1 · #1 02-13-2005, 10:32 PM

I've had my `88560SEL since Nov.

Although the A/C worked when I bought the car, I've left it
on the Economy setting most of the time I've driven the car.

I hit defrost today, which always seems to kick the fan on
high. I made a brief stop and shortly thereafter, I noticed
the unit wasn't working at all. I don't recall if I turned the
defrost off prior to it stopping.

Now, the fan isn't blowing so I can't tell if the whole system
is down or just the fan. None of the fuses, including #5 are
blown and I checked the strip fuse (as suggested elsewhere
on the forum) and it looks fine, too.

Other threads discuss repairing the climate control system,
replacing the brushes, etc. Most of those threads describe
intermittent problems with the system prior to failure that
helped pinpoint the problem.

That didn't happen for me except that I noticed when I turned
on defrost it seemed to blow high regardless of whether I set the
fan on high, auto or low.

Any advice would be appreciated. I'm a complete newbie when
it comes to this and normally have my mechanic deal with this.
Given some of the parts prices I've seen for the AC control unit,
the regulator and the blower, I'm willing to try some DIY here.

**************.com sells a little DIY kit for the replacing the
brushes on the blower motor for under $40 but I'm not sure that's
where the problem lies.

Thanks,

Bill

1988 560SEL w/131k

Thanks,

Bill

CzarFC · #2 02-13-2005, 10:49 PM

Some ideas, although I have a gut reaction for ya.

If the problem is no forced air then it's probably the blower motor. You can sorta check out the rest of the system by setting either max or min temperature and driving at interstate speeds (75mph here in Colorado) and setting the system to blow. If you feel warm/cool air as appropriate being naturally forced through the system by the air intake then the rest of the system is doing what it should but the blower is dead.

If the problem is no air, then the blower motor is probably dead. Did you get any chirping from the passenger's footwell for the past few weeks? Replacing the blower motor in the 560SEL is a real treat let me tell you. This is from the school of been there and done that, although it is easier than my 300CD.

Easiest way is to set the passengers seat in the most reclined and pushed back position possible. Then you'll be working upside down basically holding onto the headrest with your ankles. Once you have the cover removed, the motor is held in by an assembly tha uses 3 screws. Now the joy is goign to be removing the fan to place on the new motor or if you wanted to pay the extra $100 then you're new motor will have the fan pre-attached. Unless you have a dremel, epoxy, wrapping wire, and an overbearing drive to make things difficult, get the motor with the fan!

The rest is basically straightforward, but a little tedious... Not a difficult job, but it will take you the better part of a day if you've not much of a DIYer. I'm sure there's more comprehensive instructions running around, but if you get stuck I'm sure someone around here, including me, will be happy to help further.

I do not envy you the neck and back ache you'll get from this. I suggest ibuprofin or a beer!

Good Luck!

Scott

meltedpanda · #3 02-14-2005, 08:54 AM

before removing the fan check to see that you are getting power out of the ACC pushbutton unit. Should be a plug on the fan housing.
Eliminate easy stuff first.
Since the fail safe for the ACC is defrost mode , my feeling is either a fuse, pusbutton unit, or temp/fan regulator.
Let us know what you find

gidpor · #4 02-14-2005, 11:34 AM

One other thing to try and cure the "not working at all" portion of your problem is to juggle the keys with the system on to see if that does anything.
Worn out ignition switches will often do just that - disable the climate control System. On second thought - In my car only the A/C was disabled, so that might not apply to your situation - Still, it is a simple test. Also, Also, regardless of whether "None of the fuses, including #5 are blown" I would still replace that #5 with a new one. Fuses are another mysterious thing with old MB's. They might look good - But looks are deceiving.
Hope this helps you some.

benzboy87 · #5 02-14-2005, 11:58 AM

If you don't want to buy a new blower unit or install the kit yourself then you can get a used blower motor from a mercedes pre-owned parts place (salvage yard, junk yard, whatever you want to call it). I was able to get my fan to work for a couple of months by hitting the area around the fan with the heal of my hand. Might get you through for a while. Good luck, replacement requires a contortionist's skill.

backstage1 · #6 02-14-2005, 01:33 PM

Gidpor, I replaced the #5 fuse and it had no effect.
Mind you it wasn't a brand-new fuse but a matching
spare that was in the fuse box.

CzarFC, I turned A/C on and drove at highway speeds with all the
vents closed except the driver's side vent. I could feel some
air and the temperature varied from min cool to min heat.

Also, when as I toggled through the pushbuttons, I could
feel the engine adjust as the compressor kicked on and off.
That wouldn't completely rule out the problem being the ACC
unit, I guess just the fan controls could be out.

Prior to this happening, I've heard no squealing or any other
noises from the fan.

Btw, based on the info I've got, how would you know the problem
is the blower motor and not the regulator?

I guess I'll try gidpor's key trick next and then hit it with my hand
to see if that helps. Next, I'll have to round up a meter to check
to see if the fan is getting power.

I just tweaked my lower back yesterday and it hurt like hell just
changing a tire for my wife this morning. I might wait a few days
before I try to pull that fan.

So far everyone has talked about replacing the fan. What about
replacing the brushes? Is that a fairly advanced job?

Bill

meltedpanda · #7 02-14-2005, 03:23 PM

brushes are a piece of cake, just need fairly steady hands, fairly good eyesite and a low temp soldering iron

Is your vacuum working? Vents opening and closing?

backstage1 · #8 02-14-2005, 09:44 PM

Quote:

Originally Posted by meltedpanda

brushes are a piece of cake, just need fairly steady hands, fairly good eyesite and a low temp soldering iron

Is your vacuum working? Vents opening and closing?

So does replacing the brushes as effective as getting a new
heater blower? If so, that $40 kit with detailed instructions
should do the trick for me. If not, the best prices I've seen are
$151 for the blower and $275 for the blower with the fan
attached.

I'm just hesitant to spend that much time and money only
to find out the problem is in the regulator.

As far as I can tell, the vents are opening and closing. When
I took a drive on the highway this afternoon to see if I could
feel any air coming out of the vents and check if would come
out both hot and cold, I shut down the center and passenger
side vents so everything would come out on the driver's side.
It did.

The back seat vent opened and closed properly as well.

Banging on the panel where the fan is didn't do anything nor
did trying turning the key on an off while changing the cc
settings.

Bill

meltedpanda · #9 02-15-2005, 08:26 AM

on my 300SD (84) it did the trick, I replaced them at 130K. If your armature is worn badly then brushes may not help, but at your mileage I would not think that the case.
Do you have power at the connection to the fan?
Can you "jump start" (turn blower on)the ACC unit by hitting defrost?
If you cannot and you feel it is regulating the hot cold demands then it most likely is the fan, just make sure you have power to it.

backstage1 · #10 02-15-2005, 10:26 AM

Quote:

Originally Posted by meltedpanda

on my 300SD (84) it did the trick, I replaced them at 130K. If your armature is worn badly then brushes may not help, but at your mileage I would not think that the case.
Do you have power at the connection to the fan?
Can you "jump start" (turn blower on)the ACC unit by hitting defrost?
If you cannot and you feel it is regulating the hot cold demands then it most likely is the fan, just make sure you have power to it.

Ron,

Defrost doesn't work. Actually, it was shortly after hitting defrost that everything stopped working. The window was fogged up and defrost had been on for about five minutes when I stopped at a store. When I came back out, the system wouldn't come back on.

I don't have a meter so I haven't checked power to the fan. Are you saying that if there's power at the connection, the regulator is ok?

Thanks,

Bill

meltedpanda · #11 02-15-2005, 02:28 PM

others may chime in but it is my understanding that "defrost" is the fail safe built into the ACC pushbutton unit. If you cannot jump start it then I would lean to the pushbutton unit, and yes if you have power to the fan(past the regulator) then it is probably OK.
One other thing to check is the temp interlock circuit. should be a one prong temperature sensor somewhere around the thermostat housing. At least that is where it is on my 300SD. If this unit fails it will not tell the ACC to come on. It senses when the coolant is warm enough to allow unit to come on.
Try unplugging, turn ACC to all cold and see if comes on.

backstage1 · #12 02-15-2005, 10:30 PM

Quote:

Originally Posted by meltedpanda

others may chime in but it is my understanding that "defrost" is the fail safe built into the ACC pushbutton unit. If you cannot jump start it then I would lean to the pushbutton unit, and yes if you have power to the fan(past the regulator) then it is probably OK.
One other thing to check is the temp interlock circuit. should be a one prong temperature sensor somewhere around the thermostat housing. At least that is where it is on my 300SD. If this unit fails it will not tell the ACC to come on. It senses when the coolant is warm enough to allow unit to come on.
Try unplugging, turn ACC to all cold and see if comes on.

Ron, I'm not sure where the thermostat housing is. Is a temperature sensor a 3-4" long thin rod with a wire attached?

The next thing I'll check is to see if the fan is getting juice. The last thing I want to do is yank the passenger seat and replace to fan to discover the problem is in the pushbutton unit.

Thanks...

Bill

meltedpanda · #13 02-16-2005, 04:07 PM

Hmm, not on mine, I will look in my service manuals tonight.
My sensor looks alot like an oil sending plug except it sits right by the thermostat with a wire clip attached to it.
I also have a used fan speed regulator and temp regulator if you want to give them a try. I think they may be the same part. One is silver box, one is black, if you can check the numbers I will check these boxes. When I took them out they were working.

backstage1 · #14 02-17-2005, 01:21 AM

Quote:

Originally Posted by meltedpanda

Hmm, not on mine, I will look in my service manuals tonight.
My sensor looks alot like an oil sending plug except it sits right by the thermostat with a wire clip attached to it.
I also have a used fan speed regulator and temp regulator if you want to give them a try. I think they may be the same part. One is silver box, one is black, if you can check the numbers I will check these boxes. When I took them out they were working.

Ron,

I wouldn't know an oil sending plug if it were sitting in my pocket.

Other than detailing and checking a fuse or two, I've had the
mechanic do everything. Changing the blower sounds pretty
straightforward. Years ago I used to do car stereo installs so I
can handle unplugging a fan and replacing it.

I need to go ahead and invest in a CD on eBay if I want to tackle
things under the hood.

Bill

meltedpanda · #15 02-17-2005, 11:59 AM

I understand, and you have picked the problem on these old beasts that takes detective work AND some DIYer skills

Don't fret. See if you got power to the fan using a meter

turn ACC unit on off, hit fan button ect and see if meter reads, if it does then replace blower, if it does not, perhaps pushbutton unit or regualtor or or or...
we can takle that later.

Here is an article by George Murphy, the ACC guru you may find interesting

WHAT GOES WRONG...

Mono-valve: These valves frequently fail to operate because of internal leakage. Generally, the symptoms are no heat on DEF mode or full heat in all modes. Usually the rubber diaphragm inside the valve cracks and leaks. This is easy to repair--you'll need Mercedes-Benz part number 000 835 06 44, Valve Insert
The procedure for repair is as follows
First be sure cooling system pressure is released - allow engine to cool down, then carefully open radiator cap.

Find the mono-valve in the engine compartment on the firewall. Remove the 2- wire electrical connector from the coil, and undo the four assembly screws securing the top of the valve. You may have to loosen the valve mounting bracket to allow room to work on the valve.

Remove the coil (a) and shield (b). Grasp the valve insert (f), and gently pull it (along with washers c, d, and e) straight up and out of the body (g).

Make sure the internal seat inside body (g) is clean; flush with clean water if necessary. Place the new valve insert in the body, making sure the diaphragm seats into the recess in the valve body. Then place washers c, d, and e on the new valve insert in correct order as shown.

Replace shield (b) and coil (a), making sure that the notches between them align so that the coil seats properly. It may protrude slightly due to spring tension of wavy washer (d). Replace the 4 assembly screws and tighten them evenly but not too tight. The body is only plastic, and the threads are easily stripped.

Clean the contact pins and refit the electrical connector. Coil resistance can be checked using an ohmeter - it should read 10-20 ohms; or you can test the assembled valve by connecting 12 volts to the electrical connector pins momentarily. The valve should make a clicking sound.

Refill the cooling system and operate the ACC system through all modes. Check for leaks and proper operation.

Pushbutton Panel

The second most common failure that I have seen is in the pushbutton panel for the climate control.
NOTE: The repair technique outlined below for the printed circuit board has been successful in about two-thirds of the cases that I've encountered, but it is worth a try before replacing this expensive device (about $250 list price).

First, remove the unit from the car as follows: pull the knobs from radio and remove the radio molding. Remove the screws holding the lower edge of the wooden panel, then carefully pry out the lower edge of the panel to uncover the pushbutton unit.

Remove the screws holding the top of the pushbutton panel. You may have to loosen (but do not remove) the bolts in the slots on the housing. Slightly pull out the holder for the pushbutton unit at the top, and lift it out upward.

Pull off the 12-point plugs at the left and right side and the sockets for instrument lights. Remove the holder for pushbutton unit from the unit itself.

Disassembly

Remove the temperature dial by squeezing the plastic spring clips together to allow the clip to release from the pushbutton unit; carefully pry the dial unit away from the main body.

Remove the five pushbuttons from the main unit and the three pushbuttons from the blower switch by pulling them straight outward. If you need to pry with a small screwdriver, insert it under the bottom of the button and apply a counterpressue against the top so the button it is forced outward - it will snap outward off the shaft. Note which button goes where and how it is oriented (make a sketch). Remove the front plastic cover from the unit, held in place by spring clips. Remove the blower switch from the unit in the same manner as the temperature dial. Note how the light diffusers are mounted to the main unit.

Remove the bottom cover from the unit, held in place by plastic spring clips.

Carefully pry the printed circuit boards upward at the rear of the main unit so it will clear the rear of the housing. Slide it upward and out to the rear. The black side panels will probably fall off; note how they are keyed to the grooves in the main housing.

To repair the printed circuit boards, you will need a pencil-type soldering iron of no more than 25 watts, plus a small amount of fine resin core solder wire. These can be obtained at Radio Shack for a few dollars.

Inspect the printed circuit boards for burned-through copper foil. The foil side is a network of thin copper foil conductors soldered at each end to lugs or wire leads of the various parts on the opposite side. The control unit generally fails when one or more soldered connections on the foil side loosen due to vibration or heat. If you are careful, it is possible to resolder the connections and get the unit working again. For this, you'll need a steady hand and the 25-watt soldering iron (and possibly a magnifying glass to inspect your work).

Solidly position the printed circuit board, foil side up, in a well-lighted work area. Starting at one edge of the board, carefully apply heat with the tip of the soldering iron to each solder joint on the board. Caution: apply only enough heat to cause the solder around the connecting wire or lug to momentarily melt, then remove the soldering iron and allow the soldered joint to "freeze". Make sure no solder flows to an adjacent connection, or you'll have a short circuit. If the joint appears to lack enough solder for a good connection, add a small amount. Solid state devices cannot tolerate excessive heat, so use care with the soldering iron.

After you resolder each connection on the board, closely inspect for solder "bridges" between connections, which can cause a short circuit. The connections may appear slightly discolored from your resoldering efforts, but no harm should occur if you were careful with the heat. Be sure to re-solder the fillets between the "side" boards and the "bottom" board - most cracked joints are found here.

Dis-assemble the blower switch and resolder the connections inside. Note how the plastic rocker fits between the two switch halves.

Reassembly

Place the two black side panels on the printed circuit board assembly, and slide it into the main unit at an angle so that the side panels fit into the grooves in the main housing. The assembly will snap into place in the main housing.

Replace the bottom cover. Re-attach the blower switch to the right side of the main housing, then position the light diffusers and attach the front cover to the main housing. Press each pushbutton onto its respective post using the sketch you made during disassembly. Reinstall the unit in the car.

Blower motor: This climate control system operates the blower continuously whenever any button except OFF is pressed. Consequently, after 80-90,000 miles, or 5-6 years, the heater blower motor brushes usually wear down and no longer make good contact with the commutator. This is generally evidenced by a delay of several minutes before the blower starts or it suddenly starts when you hit a bump or hit it with your hand. A new blower can be expensive, so it's worthwhile to remove it and install new brushes. The brushes are fairly soft and can't be purchased from Bosch. (Don't use power tool brushes - they are too hard and will cut a groove in the commutator.)

ACC System Response Sluggish or Operates Too Cold

In M-Bs with automatic climate control, system response can become sluggish as the car (and the system) ages. This can be due to a leaky air tube for the in-car temperature sensor. The sensor is located either adjacent to the right side radio speaker or in the center of the dashboard under a small intake grill. In both cases there is a small (about 1/2" inside diameter) tube connecting the sensor housing to the suction side of the heater blower. The tube allows air to be drawn from the passenger space into the sensor housing to continually expose the sensor to inside air temperature variations.

A portion of the tube consists of foam rubber-like material which, over time, disintegrates. This allows air from under the dash to be drawn directly into the blower, bypassing the air temperature sensor.
You can check air flow around the sensor by pushing the AUTO HI (1977 to 1980) or Blower HIGH button (1981 and up) while the system is running. Place a tissue over the sensor air intake and see if the paper is drawn onto the grill - if no air flow is present, the foam hose is probably disintegrated and needs replacement.

The fix is simple - use 1/2" inside diameter foam insulating tubing for water pipes. It is usually sold in 6 foot lengths and costing about one or two dollars at most hardware stores.

Remove the glove compartment first - it is held in place with 6 or 8 plastic pin assemblies. First remove the inner pin from each assembly, then withdraw the outer pin. Snap the glove compartment light out of its hole, then carefully withdraw the box from the dashboard. Locate the sensor tube and check the foam rubber section for disintegration or blockage. If the foam crumbles easily when handled, it needs to be replaced with a new piece of foam tubing. Use rubber cement will help keep it in place.

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