Erratic ACC (A/C) Behavior - Page 2 - PeachParts Mercedes-Benz Forum

#16 08-05-2004, 08:57 AM

It sounds to me like the blower motor is working normally.

Usually the foam hose is just GONE. Since the hose was there, it may not be much of an improvement. Did it seem to be blocked or leaking?

If it doesn't improve today, you definitely need to check the connector as autozen suggested.

Have a great day,

autozen · #17 08-05-2004, 10:24 AM

Like Larry said, the blower motor appears to be working. The blower doesn't change speads on its own. It does what it's told by the ACC through a series of resistors. When a blower fails, it just quits working. If you ever need to deal with the blower, it is a walk in the park. Just drop the under dash cover on the passenger side and look up. About 4 screws and a plug disconnect, and it's outta there.

The mono valve is located on the passenger side firewall. It has a couple of hoses and a two prong elect connector going to it. In operation it pulses and controls the amt of water flowing through the heater core. as I stated when the system is off, a constant voltage is applied to the valve to keep it closed. What usually fails on this unit is the robber diaphragm inside. Just undo the elect plug, unscrew the 4 screws, and lift it out. Inspect it for tears. You can buy a replacement slug. There is no need to buy a whole new valve.

Peter

InDiesel · #18 08-05-2004, 01:18 PM

I found the blower motor and removed it. A simple exercise - thanks MB engineers. I believe that the PO let water leak in from a partially open sunroof and it looks like there was some corrosion in the motor as well as a 20 year built up grime. I used some "Lectra Clean" (spray can forund in the electical section of Home Depot) to thoroughly clean the motor itself (magnets, windings, armature, brushes, etc). Reinstalled the blower motor and now it blows hard and consistently.

The temperature still seems to vary a little even on full cold and fan on high. Will test in heat of the day today and provide results.

InDiesel · #19 08-05-2004, 08:15 PM

Update

Blower and compressor(?) is turning off occasionally (I can hear a relay click) while on full cold and fan on high. Then a few minutes later, another relay click and it is back on all while on full cold and fan on high.

Like before, when blower is on, air temp is still not always cold even while on full cold and fan on high.

Here are the actions taken up to this point:

- Resoldered ACC board (upper, lower, side connectors and pins)
- Replaced temp sensor tube (used 1/2" foam pipe insulation)
- Cleaned blower motor with "Lectra Clean"

I am going to look at the monovalve switch and diaphragm as recommended by Larry and AutoZen.

Not sure where to look next.

InDiesel · #20 08-05-2004, 09:43 PM

Checked monovalve. Seems to be working properly. When I removed the connector, the A/C air got very warm right away. Cleaned the contacts and reconnected.

Where to go from here? Temp regulator? Resolder ACC again?

autozen · #21 08-05-2004, 10:19 PM

Patrick,

You are making progress and that is commendable, but you didn't retension the female connector. Cleaning is not enough. You have to pinch those connectors. I don't know if that will solve the problem, but it will eliminate one possibility.

Peter

InDiesel · #22 08-05-2004, 10:40 PM

I will go back and retention as recommended. Thanks for the moral support as well!

InDiesel · #23 08-06-2004, 06:09 PM

Monovalve connectors retensioned - now tighter than Dick's hatband.

Same results, the A/C when blowing (on full cold with fan on high) varies in temp from very cold to cool or sometimes even ambient temp.

Next steps anyone?

autozen · #24 08-06-2004, 08:27 PM

Did you check the mono valve diaphragm for tears? I don't think that is the problem, but it is always best to check the easy things first. Next I would set the dial on full cold and roll the windows down to prevent the ETR from shutting the system down although I don't think it will, and see if the A/C clutch drops out. You can also pull over while driving when you get warm air to see if the A/C is shutting off. This would help isolate A/C control, flap control, or heater control. You're doing good on the diagnostics. This problem may end up having to monitor voltage and vacuum.

Peter

InDiesel · #25 08-09-2004, 06:44 PM

Checked monovalve - boot (spring cover) is torn, but the rubber "stopper" looks to be in good shape.

Trun system on full cold rolled down windows. Compressor is kicking off from time to time. This seems to correlate to less cold air. I am not sure why the compressor is dropping out occasionally when set to full cold and fan on high.

Seperately, the blower motor is acting up again. When I pulled it out and cleaned it before, upon inspection, the commutator was fairly grooved. The brushes still had some meat on them however. It seems that if the motor is switched on and does not turn immeadiately, it creates some kind of "burn spot" that reduces the performance of the motor. If it does "stick", a sharp rap to the underside of the passenger dash can usually get it moving again.

Should I replace the motor, the brushes, sand out the grooves in the cummutator, check the armature?

nellotare · #26 08-09-2004, 07:27 PM

just a wild thought.. is your tach working when the compressor goes out? I don't know if you have the "saftey" switch on your car, mine doesn't.

lost tach and a/c

InDiesel · #27 08-09-2004, 07:32 PM

Tach works properly. Thanks for the lead though.

autozen · #28 08-09-2004, 10:31 PM

If the diaphragm is torn, you need to replace that slug or your ACC will never work properly.

Peter

InDiesel · #29 08-11-2004, 04:25 PM

Slug is ordered and on the way

InDiesel · #30 08-16-2004, 10:36 PM

Replaced mono valve slug and blower motor.

Fan blows hard and consistently.

A/C still blows from very cold to cool/ambient on full cold and fan on high