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Old 11-03-2002, 10:32 PM
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Join Date: Nov 2002
Location: Orange County, CA
Posts: 95
Unhappy W124 Climate Control Mystery

I just recently bought an 1987 300D with 175,000 kmi in Florida and drove it back to California. During the trip, the climate control was very unpredictable.

Day 1: Started driving late PM and A/C worked until sun went down. Fan stopped blowing. (Florida)

Day 2: Before starting drive, I reseated fuses and whether that was the problem or not, A/C worked fine. (Florida, Alabama, Mississippi, Louisiana)

Day 3: A/C worked fine. SRS light started flickering on/off. (Louisiana, Texas)

Day 4: A/C worked fine. SRS light flickering on/off. (Texas, New Mexico)

Day 5: Heater came on in morning (outside temp was in 60s) and would not shut off. Also, engine would not shut off (diesel) until I used manual lever in engine compartment. Stopped in Tucson at MBZ dealer who fixed vacuum hoses in engine compartment and replaced valve to allow engine to shut off. Dealer said some sort of short was causing heater to stay on and that they could not do anything until after the weekend. I continued towards home with the windows open and the heat on full. SRS light flickering on/off. (New Mexico, Arizona, California)

Day 6: At 1:00 AM, and about 1 hour away from home, all of a sudden, the lights on the bottom of the instrument cluster started lighting up (SRS, Antilock, etc). Some type of smoke or steam started coming out above the radio (below the climate control unit). Also, the dome light next to the power sunroof switch came on. Needless to say, I pulled over and shut the engine off. It seemed that most of the light bulbs burned out on the car and the fasten seatbelts light came on next to the dome lamp and would not shut off. I turned on the hazard lights and only the left front and left rear lights flashed. I called a tow truck and brought the car to my mechanic.

My mechanic said the battery must have shorted. All the light bulbs that were on when this incident happened burned out (running lights and headlights). He also said the surge protection relay burned out and replaced it. With a new battery and a new relay, the car started. The blower fan stayed on until he disconnected it (I assume he disconnected the wire). I originally thought the heater core burst due to the high heat, but the mechanic said the coolant level was fine and that was not the problem. The SRS light remained on and he could not get any code back to diagnose it. The fasten seatbelts light remained on and I had to disconnect the wire so it wouldn’t drain the battery. Radio Works fine. After $600+, I drove the car home with no heat or A/C.


Since I want to repair the car and get the Climate Control System working again and since I have some time on my hand now, I replaced the cracked dash with a good one from the junk yard and also replaced all 7 vacuum actuators for the climate control system. I would hate to put more money into this car and have the same thing happen again.

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Old 11-03-2002, 10:50 PM
jbaj007's Avatar
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Join Date: Jun 2001
Location: Santa Monica, CA
Posts: 2,053
Check and/or replace the voltage regulator in alternator.
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)
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Old 11-04-2002, 10:10 PM
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Join Date: Nov 2002
Location: Orange County, CA
Posts: 95
Voltage Regulator is on order. I'll see what happens when I put everything back together.

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