This is probably related to my AC problems in the 300TD.

I decided to check the voltage at each terminal of the #8 fuse (AC compressor/blower, etc) against ground.

Voltage at the firewall side was ~12, but voltage at the other side (front of car) was variable and ~6. Also, that terminal was VERY hot. I replaced the fuse, and got a stable voltage ~12, but the terminal was still very hot.

When I have the AC engaged at the head unit, there is no voltage at either terminal lead to the compressor. The Blower motor (on the same fuse) works fine.

I have tried 2 head units, and the result is the same, so I don't think it is a problem there.

What should I do next - could this be due to a bad AC cube relay? ShouldI unplug the blower and see what happens?

Electrical gremlins are my worst automotive nightmare.

Help!!!!!

EDIT: Also wanted to add that there is definately a short in the tach - sometimes it registers rpm and sometimes it doesn't. I have read some linkage b/w tach and AC - could this be related?

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

These may help:



1985 300SD 617 Aux Fan & A/C Thoughts + Help Needed

617 melts fuse 11 in 1985 300SD... what's the scoop?

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Thanks Hitman!

That helped some.

The hot fuse is due to the blower. Unplugging it cools the fuse, but still no voltage at the compressor leads?


This is an 82, so no Klima....there are 2 "cube" style things in a box on the drivers side wheel well - one is 20A and the otehr 30A

Are these part of the ACC electrical relay in my car?

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

IIRC, one is for the aux fan and the other is for the a/c system (Clutch and blower). I may be wrong though.

__________________
RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Hmmm, thanks! I think you may be about right....I have a blower (though it is drawing too much power - but no voltage at the compressor or aux fan switch.....May be one out is the problem!

Feels like progress anyway.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Check for power through the evaporator thermal switch.

Attached Thumbnails

 

Whunter,

I am still reading about how to get to it...will do that and report back

I did confirm that when I plug one of the relays in (but not the other) in either spot, the fuse gets hot.
So I am assuming this relay is bad, but not the other?
Resistance across pins is the same on both units

Blower function is unchanged whether one both or none are in.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

I have voltage at the switch leads (11.4V....). Unplugging one (but not the other) relay or unplugging the switch or the blower keeps the fuse terminal from overheating.

So bad relay? Bad switch? Bad blower?

I don't understand the circuit.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT