I have a 1982 240d, 4-speed car that is now running hot with the A/C on. The temp nears the 120 mark at idle and at low speeds in traffic. It does cool down on the highway after a while as long as I keep it above 50 mph. I jumped the aux fan at the motor and it runs fine, but I'm not sure if I have more than one switch activating the fan (A/C pressure, 212 switch). I don't see a switch near the thermostat housing with an electrical lead wire, only a switch with two vacuum lines attached. Is there a 212 switch on this model? How can I test the A/C pressure switch to check if the fan is turning on when it is supposed to. Yesterday, while it was running hot at idle with the A/C on, the fan never started. The ambient temp in Las Vegas has been running around 105 so it is pretty hot anyway. Someone please point me in the right direction. Thanks

"Someone please point me in the right direction."

The search button is the best place to start.. particularly on a weekend... and much has been posted about AC stuff...

You don't have a 212 switch on that car. 212 switches were started in 85 with the 123 chassis. I think 212 were on SD's earlier. The 212 switch would be in the thermostat housing, which you don't have.

You can check the 140 (I think its 140f) trigger switch that is mounted on the receiver dryer by grounding it while the engine and the a/c is on. If the switch is bad, it can be replaced without evacuating the a/c system. I think its under $20.

You probably ought to check the area behind the aux fan since that often gets clogged with debris. You'll need to remove the fan to get at that area.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

Thanks, checked behind fan and pretty clear exect for a few desert bugs. Will try try A/C switch next. Appreciate the help.....

Tried jumping the two wires leading to the A/C switch and the fan did not turn on. I also checked the fuse for the aux. fan and it is good. Is there a relay that could be bad? If so, where is it located?

Chuck,

Have you had the radiator professionally cleaned and flow tested at a radiator shop? This may be what is needed and isn't to expensive, maybe about $40 if you R&R the radiator and carry it in to the shop.

P E H

Removal and cleaning of the Rad. will be next on the list after I get the fan to turn on. It really does not run too warm when the A/C is not turned on (80), so I tend to believe the extra load and heat the A/C generates is causing the temp rise.

Chuck,


Sure, the higher temperature air coming from the AC condenser causes the engine to run hotter if the tubes of the radiator are coated on the inside with crud. This crud decreases the heat transfer from the water to the tubes thus the water remains hotter than it would in a radiator with clean tubes.

If the buildup in the tubes gets thick enough, it restricts the waterflow in the radiator. That's why radiators are flow tested.

P E H

chuck did you try idling the car without the a/c on to see if it displays the same engine temp?

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

Chuck,

If you can't get it to run by jumping it to ground at the receiver/dryer, you have a bad fan, a bad fan relay or a bad fuse or an open wire. Since you did get it to run at one point, you can rule out the wiring.

Replace the fuse, just don't check it, replace it. You heard me say replace it, right? OK. If it runs, you had a bad fuse. Its common.

Bypass the relay. The relay is on the left front fender. If it runs bypassed, you have a bad relay.

If you have power to the fan, try manually spinning the fan. If you get the fan to turn by manually spinning it you have bad fan motor brushes.

What did you do to get the fan to run "at the motor"?????

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

Had the same problem but not as severe with my 240.

First, replace fuse as has been said. Then replace thermostat - get a good one, not junk. That solved my running hot problem.

The two relays on the left front fender under teh black box control the ac clutch and the fan - they are the same and are interchangeable, so try swapping. If you still don't get the fan, when you short the pressure switch, but you can get it on with a direct wire to the fan, it's somewhere in the wiring.

I have heard of people using the clutch relay to control the fan also - that way the fan is always on when the ac clutch is activated. Just takes a bit of rewiring. Not perfect, but might get you by.

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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer

You can't get the fan to come on by jumping the pressure switch. The pressure switch is a cut-out switch that creates an "open" when the pressure is too low, it cuts off power to the compressor.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

Must be the temp switch I was thinking of that's on the reciever/dryer. Can't keep those two straight.

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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer