Air Conditioning Idle Speed and Knobs

[CarlG]

I just got my air conditioner (kuhlmeister) working after many years and have come up with two questions.

First, Is there a source for the part that speeds up the idle when the compressor kicks in?  The shop has set the idle to 1500 for now and says he can get a part that will work but wanted me to check if the correct one is available.

Second, Are the knobs for the control switch available anywhere?  Only one of mine was still there, and the other is not in very good shape.

Thanks for any info you can provide.

[rwmastel]

Carl,
Hi.  First, you should tell us some about your car because parts are different for different cars.

Year
Model
Transmission type

I believe what you need is called an idle control switch or valve.  If your car is an automatic it should already be using this device to keep the idle speed constant when the transmission is placed into gear and the brake is applied.  This would be a good test for this part.  It should perform the same function with the A/C compressor.  Many times they are simply wired wrong.

If you have a manual trans, I'm not sure how to test it, but I guess it's not working since they set the idle so high.  I'm not sure if original parts are available, but I would assume so.  Do you have a reliable parts source?

I can't comment on the control knobs as I don't have A/C in my car.

Rodd
1966 230SL Euro
1994 E420

[Cees Klumper]

The part Rodd refers to as the idle control switch or valve, is AKA the constant speed solenoid. Automatic cars all have this, and cars with A/C should also have been fitted with it. It needs a support bracket, and some other hardware, and the appropriate wiring of course. It sits on the intake manifold side of the car, frequently wears out, is very difficult to fix (although it CAN be done) and is activated when the engine is running and the car is put into gear. It is essentially a fairly strong magnet. New ones are expensive (around $300 at my parts supplier) but I am pretty sure they were also fitted to sedans of the era. So maybe you can find one used for a more reasonable price, which I would put at $15. I picked one up that way, and it works just fine. I will be taking my old one apart to try to fix it, but this involves drilling and welding so it is not your average DIY job.
Having the idle set to 1,500 seems very unpleasant to me! How's the performance of your Kuhlmeister? Many have commented they are not that good, and have fitted more modern components, which is apparently not a big deal.

Good luck,
Cees

white 1969 280 SL

[CarlG]

First let me add the info about my car which I did neglect previously.  It is a 67 230sl with manual transmission.  I had made a post to the Yahoo site about a month ago as an introduction and also asked about the valve guide seals after one had popped off.  I am happy to report that the shop replaced all of them and it is running great now.  

In specific reference to the idle speed, I noted yesterday that it is really not that fast, more like 1,000 to 1,100, which is not too bad.  Another question asked was how was the kuhlmeister working and I must say that so far it is wonderful, quite cold and plenty of air.  It does not have the york compressor, one part of the engine rebuild was adding a rotary compressor.  I don't notice much of a difference at all in power when the ac is on either.  I should add that the temperature in Houston right now is only in the upper 70's, so I was only using the ac to check it out.  The real test will come in a few months when we add another 20 degrees to the outside air.

I note Cees comment about checking for a used one from a sedan and I will try that approach first, may be able to get a knob as well.  Thanks.

[rwmastel]

Carl,
Hi.  You should be able to check the functionality of the constant speed solenoid (thanks Cees) by opening the hood, leaving the car out of gear, applying the hand brake, and then turning on the A/C.  When you turn it on, make sure you can see through the windshield to the constant speed solenoid to watch it's action.  You may need an assistant.  Do you know what device we are talking about?  It's a cylinder about 1.5 inches in diameter and length, I believe, with a small post or arm that comes out of it.  The post pushes on a lever that actuates the fuel injection linkage and increase your idle (or keeps it constant against the increased load of the A/C).

Rodd
1966 230SL Euro
1994 E420

[Cees Klumper]

One minor addition to Rodd's post - the engine has to actually be turned on and running for the solenoid to work. Just turning the ignition key to the start position (fuel pump humming etc) does not activate the circuit that allows the solenoid to engage.
I have found that on my car, not only was the solenoid worn, but also the linkage/lever that it pushes against, had worn (nylon) bushings, and the rod linkage was dry etc. So just checking and replacing the bushings (there are two on my car, top and bottom of the relevant rod - the bottom one is hard to get to and goes through a space in the exhaust manifold) and also cleaning, smoothing and lightly greasing the solenoid-to-linkage metal surfaces that contact each other, may already get you there, without having to do anything to the solenoid switch itself. The nylon bushings cost next to nothing. In general, it is wise to always ensure that your fuel linkages are smooth, that the bushings are not worn (including the two bronze ones supporting the big central rod that crosses over the engine to connect the two main (passenger and driver's side) parts of the linkage, and that it is adjusted properly. Tom provided an excellent procedure description for this in the "low idle" topic that is wortwhile to print out and post to the inside of your hood (bonnet)!

Cees

white 1969 280 SL

[n/a]

Carl,
I have the constant speed solenoid (and have no evidence that it is not working properly). Call me and I can come by so that you can see what it looks like and how it is mounted.
My a/c works fine, even in the Houston summer heat. It is converted to 134A and I assume it has the original compressor, but maybe not. I an interested in seeing what your installation looks like.


Regards,
Stan

[n/a]

I, like Carl am in search of a/c knobs and the small black plastic surround that covers the nut that holds the threaded switch stalk to the a/c unit front panel.

Regards,
Stan

[DavidAPease]

I don't have A/C, so this is an uneducated response, but here goes.  I've seen many pictures of Kuhlmeister and other A/C units.  Some of them seem to have knobs that match the rest of the dash.  If I were looking for knobs, the first thing I'd try to ascertain is whether a Becker radio knob would fit the A/C shafts.  If so, I'd contact Ed Ebel at Becker USA and order knobs that match the rest of my dash.  (Large flat ones for the later cars are cheap; smaller, deeply dished ones for the earlier cars are rather expensive.)  Obviously, you'd miss having any kind of pointer on the knob, but the matching look would be worth it to me.

-David Pease
'66 French 230SL

[ja17]

Hello Carl,
This high idle probably makes the transmission downshift hard also?
Anyway, Rodd is correct in that the different years had some different style knobs etc. Many old W111,W112, W110, W108, W109 series Mercedes sedans and coupes had the exact same controls and knobs. These Mercedes were built between 1963 and 1972, find a sedan close to the same year. The knobs should match those on your dash.
I am sure that your rotary compressor makes a wonderful upgrade since it robs less power and has very little vibration then the old York unit. It would be nice to know who supplies the mounting bracket and what compressor make was used?

Joe Alexander
Blacklick, Ohio

[CarlG]

In response to Joe's question about the make of the compressor and the adaptor plate, the compressor is a Sandin (not sure if that is the correct spelling) SD508.  The adaptor plate is very common and will be carried by any vendor who carries Sandin compressors.  It is made to go between the Sandin compressor and the york mount.  It works in old Porsches and BMWs of that timeframe also.  Because the new compressor is smaller than the York, there is no problem fitting the new plate and the compressor in the place where the York was.

Also, in response to the suggestion that maybe the radio knobs would work, I checked that before I made the post as my old Becker radio is in my garage.  They are just a little bit too small to fit on the AC rods.  It may be possible to file down the rods just a bit, but I am still looking for the proper knobs first.  I don't really need new ones as the front of my AC panel looks its age.  Is there a way to clean the front plate without losing the printing?

[ja17]

Thanks for the info Carl. What year is your car, do you have the early small or  large late knobs.

Joe Alexander
Blacklick, Ohio

[CarlG]

I am trying adding some info about my car to the signature block.  Hopefully that will make it show every time.  The car is a 67 230sl with the small knobs.  Actually, right now one of them is a large knob from a porsche, looks funky, but works.

1967 230sl (stick)