Need help with A/C vacuum switch ID

andy72 · Mar 2, 2017

I'm rebuilding the heater/AC box on my 72 Mach and I believe this switch isn't working correctly.

I believe I've seen this switch, #C7ZZ-18C311, on another post and it had a spring in it.

That post was by '72HCODE' way back in 4 of 2011. It is an excellent explanation of all the vacuum controls

on an AC box. I plan on using it this week to verify my rebuild. Anyway,

my switch only pushes and pulls in and out. It seems like it should have a spring in it to return it to it's "normal" position.

The pictures on Summit, Scott Drake, ect.. don't let me see if there's a spring in it.

The switch works otherwise. One position allows air flow through it , the other doesn't.

Can someone verify?

Thanks

secluff · Mar 3, 2017

andy72, all the info I have does not show a spring on that switch. Ford called that a Servo control switch. The actual part number is C6OZ-18C311-A. Since it was used on cars with integral AC, it saw use in the Mustang line starting in 67. That's where some of the C7ZZ part numbers are coming from since some of the switches had C7ZF engineering numbers. It had an internal spring which could fail and cause your system to not switch from floor to defrost. Ford discontinued it around 1995 but there are still some original units available at some vendors. Considering the age of them the repo's are probably a cheaper and better buy. I would check with Don (Ohio Mustang Supply) to see if that is something he stocks or can order. You can also search by the C6OZ part # if you wanted to search on line.

andy72 · Mar 3, 2017

Secluff,

I'm slightly confused. Scott Drake lists that part as C7ZZ-18C311, A/C Vacuum Switch. It seems like it would have to have an internal spring. The lever on the heater box would depress the switch, and the spring would return the plunger to the out position when the lever moves away? They are 40 bucks at Scott Drake and up to 56 bucks at NPD. Expensive little part. That's why I want to know if I need to replace mine.

I hope this is a correct assessment and that mine should have an internal spring as you mention in the middle of your reply?

When you say "does not show a spring on that switch", I assume you are referring to an external spring?

Andy

rocket366 · Mar 3, 2017

yes it has a spring in it.

When the heater control is moved to cold the vacuum switch stops engine coolant from entering the

heater core via the action of heater control valve.

Paul

secluff · Mar 3, 2017

Andy, I should of clarified a little better. There was no external spring on that unit. It had a internal spring which could fail and cause it not to function. With the newest one from Ford now 22 years old it would be cheaper and safer to use a repo switch. C6OZ-18C311-A is the correct and only official Ford part number and was sold by that number until discontinued in 1995 . It was used on various Ford/Mercury vehicles with integral air (AC in the dash and not the Ford air that hung below the dash). Since it was used in the Mustang line starting in 67, the engineers responsible for the Mustang line may have requested some sort of change that resulted in a "C7ZF" ID number. That is probably where some of the part vendors are coming up with the C7ZZ part number.