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77 450SL, 79 450SLC 5.0, 67 250SL, 61 190SL, 61 190, 62 180;Others:www.cardomain.com/id/challenger_7
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Discussion Starter #1
Hi All.
I am new here, and I can see this is a great forum.
I purchased my 79 SLC about a year ago, and just started fixing the few snags in it a few months back.
The car is still in an almost immaculate condition, seats, body and suspention and I am working through the few little things that are not right.
The A/C cools fantastically well but I suspect that the buttons are not giving the right functions, and I need to know how they should perform.
The "Lo Auto": Am I right in assuming that air should blow only from the front openings and none from the "defrost vents" below the screen?
Same for Hi Auto?
Then Bi Lebel should blow from both front vents and defrost?
And finally the defrost should blow fully from the upper screen vents?
Can someone comment please, or direct me to a thread that deals with this topic, as I could not find one.
I have other questions but will wait till these get cleared.
Thanks for the anticipated help.
 

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2017 Police Interceptor Utility, 2017 Police Interceptor Sedan
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You're correct, except that Bi-level is defrost and floor and is not used for A/C, but for heat.
 

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77 450SL, 79 450SLC 5.0, 67 250SL, 61 190SL, 61 190, 62 180;Others:www.cardomain.com/id/challenger_7
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Discussion Starter #3
Thank you flyboyike. Thats one thing clarified and cleared.
On the temp control, can you explain what happens when I move the temp dial?
Example, if the temp dial is on the lowest setting, then I move it higher up, for a warmer climate, is there a sesnsor that senses the temp? If yes, where is it located?
How does it control? Does it switch the compressor on and off to maintain the desired temp or does that by adding then shutting hot air?
Thanks for your contribution.
 

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The interior temperature sensor is on top of the dash. The resistance there and at the temperature wheel are transmitted to the climate control amplifier behind the glove box. The amplifier, in turn, commands the climate control servo to open or close. The A/C compressor activates only if the compressor switch is in the ON position.
 

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77 450SL, 79 450SLC 5.0, 67 250SL, 61 190SL, 61 190, 62 180;Others:www.cardomain.com/id/challenger_7
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Discussion Starter #5 (Edited)
Thanks again buddy. This sure helps a lot, but please bear with me for one final (hopefully) question, as I am by no means an expert in this field. When you say the Amplifier commands the climate control servo to open or close, where is the servo located and what is its function? What happens when it opens or closes? Does it control the refrigerant gas or what exactly.
Forgive my basic questions but only when I understand the system, that I can hope to repair it.
Regards
 

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See the pic. The servo is located near your firewall, on the passenger side. Essentially, it's an overly complex coolant flow control valve. The more it opens, the more coolant is allowed to flow into the heater core, so, ostensibly, when you temperature wheel is on max, it would be fully open. Conversely, when you're on min, it's fully closed and the air gets into the cabin goes over only the very cold A/C evaporator and an empty (and therefore not hot) heater core. Next to the servo you will find the auxiliary water pump, see pic:



Its job is to supply the servo with coolant at a constant pressure regardless of engine rpm.

The whole system is on the face of it a good idea, but in practice turned out to be very unreliable. The servo is made almost entirely of plastic and has a propensity towards cracking and/or internal mechanism failures. This was originally a Chrysler piece and was unreliable enough that even Chrysler dumped it. Mercedes picked it up and produced it until 1980.

If yours is shot (odds are it is), replacements are available with an all-metal body (less tendency to crack). Also, there are electronic solid state valve kits available.
 

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77 450SL, 79 450SLC 5.0, 67 250SL, 61 190SL, 61 190, 62 180;Others:www.cardomain.com/id/challenger_7
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Discussion Starter #7
Thanks indeed again Ike for your valuable input. As you have rightly guessed, both were shot, and I got replacements from Tom Hanson.
If I had consulted this forum, I would have opted for the all steel one :-(
As u also rightly pointed out, I did recognize the brown lower part of the servo which is identical to what I have on my 71 Challenger, same goes for the vaccuum distributor behind the A/C puch buttons to which all the vaccuum pipes connect to. So ur spot on again there.
Anyway, I still do not have water going through the pump and suspect wrong running of the hoses.
Can you please also guide me on which hose goes where? Is there a diagram for this?
BTW, the servo that I have (like my previous one) has 4 water connectors where as the photo you displayed shows only 2, unless it is the way the photo was taken?
Thanks again buddy.
NB. I too am a flyer, but a much smaller one PPL single engines ;-)
Cheers
Farouk
 

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Proceed over to the R107 forum, somebody on there is bound to have a diagram laying around. Now, when you say you're not getting water to the pump, do you mean the servo or the aux water pump?
 

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Discussion Starter #9
OK will try at R107. On the water, the way I saw the car's water hoses connected was water coming from the servo to the aux pump and then out from the aux pump to the heater core. But even then, you could feel the hose hot only to a certain part but not all the way to the heater core. So we will be playing around with the hoses today pending some firm confirmation as to the correct layout.
Thanks again for your input.
Cheers
 

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OK will try at R107. On the water, the way I saw the car's water hoses connected was water coming from the servo to the aux pump and then out from the aux pump to the heater core. But even then, you could feel the hose hot only to a certain part but not all the way to the heater core. So we will be playing around with the hoses today pending some firm confirmation as to the correct layout.
Thanks again for your input.
Cheers
It looks like your car has been all mishosed (is that a word?). It's supposed to be radiator to aux pump, aux pump to servo, servo to heater core.

Question: with the ignition key in the on (but not start) position, do you hear a whirring sound from the servo? You may have to lean pretty close to it to hear it.
 
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