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AC Low Limit Switch

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apannizzo View Drop Down
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    Posted: Jul/11/2018 at 12:06pm
I have a 1974 AMX with a 360 with AC. My Mechanic just refilled with Freon. The AC is working fine. My Mechanic could not find a low limit switch on system. He says if pressure gets too low without a Switch my Compressor could Blow. My questions are- Is there a Low limit Switch on the System? If so where would I find it? If There is one and my Car does not have it , is it easy to Install? If someone could also send pictures to my E mail at dpannizzo@hotmal.com Of what it looks like that would be a great help!

Thanks Again!

Al
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billd View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2018 at 12:23pm
Since this is an AC (HVAC) question and not related necessarily to any specific engine, moved to the HVAC section.
Thanks.

Wish I knew on the 74s, I can tell you on the later models - there's a switch next to the sight glass up front left side.
Follow the line to the condenser, and from the condenser. They are typically there in one of those lines or near the compressor. I'm talking GENERICALLY, not necessarily AMC. If I get a chance the TSM would tell me - but maybe someone like Ross, etc. will chime in before I get to it.
Good luck - and yes, there needs to be a switch of some sort to protect the compressor. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2018 at 12:29pm
The only swith I know of that regulates flow is valve on the evaporator, which under the dash. If replacing with R12, there is a replacement type made for the R134 conversion. Unfortunately I have no part number on me, though Farna has it in his reference material. The issue is newer freon requires higher pressure, so the older valve will not properly adjust, which will not cool things down properly. Nobody has posted issues with leaving the old valve in place, but many have done the change, while restoring their cars, while they have the chance.

The other switches are on the back side of the control panel.

It's not impossible to get to, but it requires the dash and front section to be removed, to change it, and probably requires the unit to be pulled to properly remove the old valve, without damage. And loss of your freshly charged system.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2018 at 12:38pm
There will be a switch to shut the compressor down in event of low pressure, or there should be on that vintage.
The electronics under the dash would be thermostat, etc. and those only control the compressor on/off cycle based on temperature of the air.

The TSM will tell if anyone has one and cares to look. I'll look in a few minutes........
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2018 at 1:12pm
Well what do ya know - AMC didn't protect the compressor with a low pressure switch. SOME models had an over-pressure switch, but the 70 series had NOTHING other than a fusible link to the compressor.
For some reason AMC handled AC differently on different models (likely the design engineer, whatever, and I've talked to one of those personally who worked for AMC doing electric and he said part of these things were up to the person and it could change if a new person came in or someone was moved, etc. - ideas went with them.............)

Anyway, no switch other than the thermostat inside like 304dude said - but there IS a link wire for Javelin and Javelin/AMX.

They were unusual in not having a switch at all other than the thermostat inside and the fusible link to the compressor. Whatever works/worked. It worked for them........... and maybe those old compressors were more forgiving. 

So the answer is no low pressure switch, only a thermostat inside like 304 explained, and the fusible link outside to the compressor. 

You can "hot wire" the compressor to see if there's refrigerant in it or if it's low-  using the sight glass - it will have one of those. 
You'll need to trace back and see where the power stops to the compressor - the link or the wiring in the dash, etc.
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