Slant Six Forum :: AC thermal clutch cycling switch on 71 factory AC

Quote:

Going to a thermal-only switch would not be a wise idea, especially with your impending change to R134a. That lever is what moves when you slide the temperature lever towards or away from "Cold". Move it more towards "cold", and the clutch switch keeps the compressor engaged longer. Move it more towards "warm", and the compressor is engaged for shorter periods. Delete this function, and you will have only one option: Full-cold, no adjustability. Why would you want that...?

Well, to be fair, that IS how just about every other car on the planet except the A-body Mopar works

The EPR systems all give "full cold all the time" and then blend heat for warmth. The later CCOT systems do too. So do CCOT and VOV systems on GMs, Ferds, most asian imports.

The A-body system, though, is BY FAR the best thought-out of the Mopar AC systems in terms of compressor control. Light-years ahead of EPR, and shifting the set-point of the thermal switch in response to temp lever position makes sense, saves fuel, and makes you wonder why they all don't work that way.

Author:	AnotherSix [ Mon Jan 22, 2007 2:53 pm ]
Post subject:	AC thermal clutch cycling switch on 71 factory AC
Well I just tore into my dash to install a new AC / heater control switch. I am also going to change the factory AC over to r134, so I decided to install a new clutch cycling switch at the same time while there is some access to the box. I already knew there was a switch in there and it is probably fine, but I want it all to work without trouble when I get finished. The surprise is that the thermal cycling switch in there also has a cable actuated lever on it. I was not expecting this. I suppose it is the main switch to turn the compressor on and off. If this is the case I cannot just swap it out for the new thermal only switch. Is anyone familiar with the compressor circuit and this switch on the 71?

Author:	SlantSixDan [ Mon Jan 22, 2007 7:16 pm ]
Post subject:
Going to a thermal-only switch would not be a wise idea, especially with your impending change to R134a. That lever is what moves when you slide the temperature lever towards or away from "Cold". Move it more towards "cold", and the clutch switch keeps the compressor engaged longer. Move it more towards "warm", and the compressor is engaged for shorter periods. Delete this function, and you will have only one option: Full-cold, no adjustability. Why would you want that...? The switches don't make much trouble. If the one you have is working, there's not much reason to replace it. But if you feel you must, use the correct lever-operated type. Read this thread and the links off it.

Author:	Charrlie_S [ Mon Jan 22, 2007 7:20 pm ]
Post subject:
If I remember correctly, that is the temp control switch. It works like a refrigerator temp control. The cable is connected to the dash control. It is not just a freeze out control.

Author:	AnotherSix [ Tue Jan 23, 2007 9:47 am ]
Post subject:
Thanks for the input. When I was working on it I tried moving the temp cable and it did not move the switch. Last night I was thinking the switch might be linked to the defrost or Max functions and vacuum operated. I looked at things more and found that the previous owner disconnected some of the linkages on the box to get the heater to work without replacing the main switch. So I have to hook a few things back up to get it working . My main concern was that getting the capillary tube into the evaporator would be a real hassle if I had to change it down the road. But it is actually very easy to get at, so I am just to going to leave the switch alone. I have a factory manual on the way which will make this all much easier. Thanks again.

Author:	440_Magnum [ Wed Jan 24, 2007 2:06 pm ]
Post subject:
Quote: Going to a thermal-only switch would not be a wise idea, especially with your impending change to R134a. That lever is what moves when you slide the temperature lever towards or away from "Cold". Move it more towards "cold", and the clutch switch keeps the compressor engaged longer. Move it more towards "warm", and the compressor is engaged for shorter periods. Delete this function, and you will have only one option: Full-cold, no adjustability. Why would you want that...? Well, to be fair, that IS how just about every other car on the planet except the A-body Mopar works The EPR systems all give "full cold all the time" and then blend heat for warmth. The later CCOT systems do too. So do CCOT and VOV systems on GMs, Ferds, most asian imports. The A-body system, though, is BY FAR the best thought-out of the Mopar AC systems in terms of compressor control. Light-years ahead of EPR, and shifting the set-point of the thermal switch in response to temp lever position makes sense, saves fuel, and makes you wonder why they all don't work that way. On the other hand, the blower and ducting in A-bodies- at least the later ones- is freakin' stone-age compared to the B's and C's. Why bother with in-dash air if you're going to just tack 3 cheesy-looking vents under the dash ane make it LOOK like under-dash air?!?

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Author:	SlantSixDan [ Thu Jan 25, 2007 8:05 am ]
Post subject:
440_Magnum, your comments are right on!

Author:	Charrlie_S [ Thu Jan 25, 2007 8:44 am ]
Post subject:
Quote: Quote: Going to a thermal-only switch would not be a wise idea, especially with your impending change to R134a. That lever is what moves when you slide the temperature lever towards or away from "Cold". Move it more towards "cold", and the clutch switch keeps the compressor engaged longer. Move it more towards "warm", and the compressor is engaged for shorter periods. Delete this function, and you will have only one option: Full-cold, no adjustability. Why would you want that...? Well, to be fair, that IS how just about every other car on the planet except the A-body Mopar works The EPR systems all give "full cold all the time" and then blend heat for warmth. The later CCOT systems do too. So do CCOT and VOV systems on GMs, Ferds, most asian imports. The A-body system, though, is BY FAR the best thought-out of the Mopar AC systems in terms of compressor control. Light-years ahead of EPR, and shifting the set-point of the thermal switch in response to temp lever position makes sense, saves fuel, and makes you wonder why they all don't work that way. There are advantages to both the clutch cycling sw and the POA/STV systems. The clutch cyclig sw is cheaper to build/install, and will return better fuel milage. The POA/STV system will give better humidity control. Newer cars use a clutch cyling swich to prevent evap freeze up, and blend warm air for temp control. That is a compromise to help fuel milage, and provide better humidity control, by keeping the evap at a low temp. Some newer cars have a Variable displacement compressor, that changes its cooling capacity, according to the heat load. This gives excellant humidity controll, and at low loads, improves fuel milage. Some really new cars are using a electronically controled compressor, that does not even have a clutch. The compressor runs any time the engine runs.

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