The pc board in the push button control assembly in my '83 300D slowly
burned up. I could smell it for awhile but couldn't pinpoint it. Finally
the blower and compressor stopped and the pushbuttons froze. I bought a
used pushbutton assembly, a temperature control unit, and a blower speed
control unit, but couldn't find a blower resistor unit (located over the RF
wheel).
While the Electrical Troubleshooting Manual was very useful in testing the
circuits connected to the Climate Control units, I couldn't find many
resitances or amperages with which they could be tested except for the
monovalve (15 ohms) which was okay.
The blower resistors in series showed declining resistance as follows over
the six connections:
All resistors in series (terminals 2 to 5) 2.8 ohms.
As each resistor was eliminated in series: 2.6 1.8 0.8 0.6 0.2 ohms
Separate resistors showed the following: 1.2 0.6 0.4 0.4 0.3 ohms
Visually the resistors looked good.
Old DM was bad so measurements were made with an old VOM.
A path on the PC board to connector #10 on the left hand side of the PC
board appeared to be burned. (See picture.) According to the manual this
connects to the defrost flaps switchover valve electromagnet. I checked
this connection and got no resistance so it seems that the electromagnet may
have shorted out and then burned out.
Would like to hook everything up in hopes of having some air conditioning
but since the cause of the pushbutton unit burning up couldn't be definitely
determined, I don't want to just put it back together and hope that it won't
burn up the replacement units.
If someone who has a 300D/300CD/300TD; 123.133-153-193 could take out the 16
amp fuse #8, the 8 amp fuse #14, connect an ammeter across the fuses
terminals one at a time , and take a reading of the amps on across each fuse
terminal with the air conditioner and fan running on high; I could do that
on my car to see if the amps are approximately the same. If so, it would
hopefully be safe to run my A/C. If the Defrost flaps switchover valve is
actually burned out and causes the A/C to be inneffective, I'll have to pull
the dash and replace it. Help on this repair will be greatly appreciated.
Also, can someone tell me which is the best general purpose DM on the
market?
Thanks,
Gerry
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