Still sorting out the small bugs in my new-to-me 240D. I love the manual climate control (verses the push button debacle in my 300D) but it has a peculiar quirk. Most times when I move the blue temp wheel to the cool area and turn on the fan, the fan comes on in fine order but the compressor does nothing and blows just ambient air.....however a while later driving down the road I may try again and feel the compressor kick in and the cooling begins. I thought at first that perhaps the compressor would not engage because of the low pressure switch but surely it wouldn't come and go as it's doing. The only thing I could find by searching related to this problem was that the ignition key sometimes affects the climate control. Any help on this intermittent problem?

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85 300D 107K present
82 240D 190K present- next-to-slowest car I ever owned
81 240D 1995-2000- slowest car I ever owned
79 350 SE Euro 1996-2001- fastest car I ever owned

Ok, two points:
I have seen bad ignition switches give some really wierd climate control results. One car I had , the fan would sometimes not work. Then I would turn the key back, just a touch and the fan would run fine. I replaced the switch and all was well with the car.
On my '83 300D, it has the R4 compressor. The connections on it are not always great. Just a pair of 1/4 in female connectors in a common plastic housing. If that is what you have, try cleaning the connectors and maybe pinching the metal part a bit to get a solid electrical connection.

OK....not the ignition switch and I giggled the wires going to the compressor to see if the connection was bad. Compressor still didn't kick in. I thought I would next try to jump the connecting wires to the low-pressure switch for a half-second to see if it will turn on....but that seems unnecessary because I already know that the compressor kicks in sporadically. If the system was low on Freon, the compressors would NEVER come on instead of hit and miss...correct?
Thanks

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85 300D 107K present
82 240D 190K present- next-to-slowest car I ever owned
81 240D 1995-2000- slowest car I ever owned
79 350 SE Euro 1996-2001- fastest car I ever owned

The compressor will "cycle" more when freon is low. When the froen level drops below a certain pressure point, I do not know off hand what that is, the compressor wil stop kicking in.

Use a volt meter and check for 12v at the compressor connections. Do this with the engine off. Put the ignition switch in position 3, and turn on the A/C. If you are getting 12 volts, and the clutch is not engaging, could be a bad clutch.

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RRGrassi


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

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

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

Good thought....and if there is NOT 12 volts at the compressor with the ignition switch in position 3 and the A/C set to come on, then this would mean the problem is BEFORE the compressor? Thanks!

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85 300D 107K present
82 240D 190K present- next-to-slowest car I ever owned
81 240D 1995-2000- slowest car I ever owned
79 350 SE Euro 1996-2001- fastest car I ever owned

I may be wrong on this, but it is my understanding that the clutch is not supposed to cycle on this system. If this is true, I would suspect a restriction, such as the expansion valve or accumulator. Or, as you mentioned, a low charge of refrigerant.

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Sam

84 300SD 350K+ miles ( Blue Belle )

You're saying on a 240D the compressor is not supposed to cycle? Runs all the time?

__________________
85 300D 107K present
82 240D 190K present- next-to-slowest car I ever owned
81 240D 1995-2000- slowest car I ever owned
79 350 SE Euro 1996-2001- fastest car I ever owned

WOW! I have the EXACT SAME PROBLEM with my 1983 240D. AC sometimes chooses not to work. I tried solving this problem too thinking that maybe the freon level was low. I had the pressure tested and it was fine. After having the system completely checked, I gave up, learning to live with the AC hesitation, as my experience has been that it may take awhile, but the AC always comes back on. My delay has never been longer than 3 to 5 minutes.

Ok folks...I got back to the 240D this weekend. Here the results of the tips. (1) When I jump across the low pressure switch, the compressor does not kick in. (2) There is 12V at the compressor with the controls set for the A/C to come on, and no voltage at the compressor when the A/C controls are set for the A/C NOT to come on. (3) Switching the relays doesn't result in any change and (4) A jumper wire across the relay socket as Gene suggested to try also did not cause the compressor to kick in.

Since when the controls are set for A/C, there is 12V at the compressor leads but the compressor does not pull in, does this mean the clutch and/or entire compressor is bad? Can a clutch be an intermittent problem? Thanks for you continued help.

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85 300D 107K present
82 240D 190K present- next-to-slowest car I ever owned
81 240D 1995-2000- slowest car I ever owned
79 350 SE Euro 1996-2001- fastest car I ever owned

O.K. If you are getting power to the clutch at the right time. And the clutch does not kick in... try one more thing, unplug the clutch. With the key OFF. Use a jumper wire and go from battery to clutch, if clutch does not kick in, you know it is the clutch.

I'll give it a try. When I connect a jumper from the battery to the leads on the compressor, do I need to be concerned about polarity? If so, do you remember which spade connector on the compressor is the pos and which is the neg? (left being passenger and right being driver sides).

__________________
85 300D 107K present
82 240D 190K present- next-to-slowest car I ever owned
81 240D 1995-2000- slowest car I ever owned
79 350 SE Euro 1996-2001- fastest car I ever owned

I will check mine later today and post.

The brown wire is ground. It is on top if at 3:00 The clutch will kick on either way. Do not know if you should, I am just saying it will.