560 SL Air Cond not coming on every time.

Once in a while my A/C does not come on when I start the car. (three times so far) Twice it eventually came on, but once I had to shut the car off and restart, then it came on immediately. Turning the system
off at the dash and then back on does not make it kick in. I think the system is a little low on refrigerant because the sight glass is milky. (But it does blow cold if it is not too hot outside.) I am having the refrigerant checked/filled up today. The question is, can low refrigerant cause the whole system to refuse to come on? Blower fan too? Seems like the fan should run regardless. But maybe there is a sensor that prevents the system from coming on under certain conditions? Like high outside temperature? It was about 92 yesterday here in Phoenix. '89 560SL
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If you are talking about not having any fan control... it would be the ignition switch that needs to be replaced... you can try one thing... with enging running... turn back the key just a bit more without shutting engine off... usually the spring is bad and the switch won't return to 'on' position.
Check fuse... and check freon level.
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Hi
My 560SEL I thought had a low refridgerent pressure switch that stops the compressor running and damaging itself if there is no 'juice' in the system.
Cheers
Neil
1998 C240T 1998 SL500 1950 Land Rover

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Thanks for the input. Had 12 oz of R12 put in yesterday. $75 whew! Worked fine this morning, but it is not hot yet today so I will have to wait to see if that is a factor. I also read that there is a sensor that measures engine tempurature that can give a false reading of excessive engine temp. and shut off the air. Keeping fingers crossed in Phx. Summer is coming fast.
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yeah, mine does that as well.... it's getting a bit tiresome to keep turning back the key a 'tad'. How the heck does one take that switch out? i've been looking at it and given up so far.
cheers, guenter
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WIth the underdash off... you need to turn key into ACC position and then pull the wire plug out on the back. Turn the key back to off... and remove the switch with stubby flat screwdriver. Three of them.
Now, before you stick that new switch in... make sure the slot position match the old switch... otherwise, if you force it in. you will break that tab inside the ignition lock and will need to change out that whole lock... cost alot more.
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stubby flat screwdrivers. Stubby presumably because there isnt' much room but why 3 of them? Geez, I've got enough problems dealing with one correctly :-)
cheers
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..... screws, three screws ..... takes a while sometimes.... :-)
thanks again Tiger
ps I initially had the impression that the return spring was in the tumbler mechanism, but I now realize that it's the rear electrical part of the 3-part ignition switch (Tumbler, housing, electrical switch) Correct??
cheers, guenter

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I meant three screws needed to be removed by one stubby flat screwdriver... not three screwdrivers... Yes, space is incredibly tight... you can use a skewdriver... which is an angled screwdriver where you twist the handle and the screwbits will move... you will need the 1.5" screwdriver bit.
Yes, the spring is in the ignition switch part.
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