I have problem with my 1973 Mark IV ac.
The pressure switch is damaged. Could anyone tell from where I can buy a new one.
Please. look at attaches pictures
1973 Mark IV ac problem
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- Lee
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Re: 1973 Mark IV ac problem
I don’t see that switch in your schematic, but I believe it serves to protect the compressor in the event Freon is low. If you know you have a full charge, you can jump those connections.
1930 A Coupe
1941 LC Coupe
1968 XR-7 (my great-grandfather’s)
1962 LC Sedan (owned 35 years & driven 100k+ myself)
1941 LC Coupe
1968 XR-7 (my great-grandfather’s)
1962 LC Sedan (owned 35 years & driven 100k+ myself)
- TonyC
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Re: 1973 Mark IV ac problem
Not an expert on '70s systems; but if my guess is right, the OP's pressure switch is called the "40° Ambient Cut-Off Switch" in the schematic. If the plug has two black wires with yellow stripes, then that confirms it. But Lee's description of its purpose sounds plausible.
Not sure where one can get a good replacement; but if the part stores do not have listings for it, E-Bay has been very good to me when I'd been in need of new parts. Keep in mind, however, that you may have to empty out the system to replace it, if it isn't already purged of freon.
---Tony
Not sure where one can get a good replacement; but if the part stores do not have listings for it, E-Bay has been very good to me when I'd been in need of new parts. Keep in mind, however, that you may have to empty out the system to replace it, if it isn't already purged of freon.
---Tony
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1966 Continental Sedan, affectionately known as "Frankenstein" until body restoration is done (to be renamed "General Sherman" on that event)
"Question Authority!"
1966 Continental Sedan, affectionately known as "Frankenstein" until body restoration is done (to be renamed "General Sherman" on that event)
- Lee
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Re: 1973 Mark IV ac problem
I saw the 40* switch, but I thought those were in order to disable the compressor in cold weather. I don't know why it would need to tap into pressure, but I've been surprised before.
1930 A Coupe
1941 LC Coupe
1968 XR-7 (my great-grandfather’s)
1962 LC Sedan (owned 35 years & driven 100k+ myself)
1941 LC Coupe
1968 XR-7 (my great-grandfather’s)
1962 LC Sedan (owned 35 years & driven 100k+ myself)
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Re: 1973 Mark IV ac problem
I think it's just a terrible name for a low pressure switch. If it's 40* outside the vapor pressure of the refrigerant will be low and prevent the system from coming on.
The Mark iii doesn't have a pressure switch on the system so I am guessing this might be the first model for such a thing? My guess is they were being creative with the names of new sensors. IMO the name would imply it's a type of ambient air temp sensor which it definitely is not.
The real question would be how a r134a conversion would change the equation of that sensor...
The Mark iii doesn't have a pressure switch on the system so I am guessing this might be the first model for such a thing? My guess is they were being creative with the names of new sensors. IMO the name would imply it's a type of ambient air temp sensor which it definitely is not.
The real question would be how a r134a conversion would change the equation of that sensor...
55 Chevy 2 dr/ht pro street 427
71 Lincoln Mark iii
2004 Dodge Ram 1500 Rumble Bee #1168 of 4000
71 Lincoln Mark iii
2004 Dodge Ram 1500 Rumble Bee #1168 of 4000
Re: 1973 Mark IV ac problem
The shop manual tells about cut-off switch: The switch is preset to open the magnetic clutch field coil circuit when the system pressure drops below approximately 40 psi (276kPa)
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Re: 1973 Mark IV ac problem
Is that sensor on the high side? 40 PSI seems to be to low for it to be on the low side. I think 40psi would be normal operating low side pressure for a day where the weather would be mid 60s.
55 Chevy 2 dr/ht pro street 427
71 Lincoln Mark iii
2004 Dodge Ram 1500 Rumble Bee #1168 of 4000
71 Lincoln Mark iii
2004 Dodge Ram 1500 Rumble Bee #1168 of 4000
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Re: 1973 Mark IV ac problem
I zoomed in on your photo and noticed that sensor is not factory on that car since it's stamped "R-134a". I would assume the switch on there is some universal binary pressure switch like this.
https://www.summitracing.com/parts/fss-36646
You could do some research on the Four Seasons website and easily be able to match it.
Also noticed those are not standard 134A conversion fittings and looked to be part of the line. Does this car have an aftermarket AC system or custom lines?
https://www.summitracing.com/parts/fss-36646
You could do some research on the Four Seasons website and easily be able to match it.
Also noticed those are not standard 134A conversion fittings and looked to be part of the line. Does this car have an aftermarket AC system or custom lines?
55 Chevy 2 dr/ht pro street 427
71 Lincoln Mark iii
2004 Dodge Ram 1500 Rumble Bee #1168 of 4000
71 Lincoln Mark iii
2004 Dodge Ram 1500 Rumble Bee #1168 of 4000
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