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My 68’ Factory A/C Thread

451 Views 12 Replies 4 Participants Last post by  matnetik
I have 68’ Mustang with factory A/C. I have been wanting to fix the A/C for some time now and was planning on doing it during the winter. Well the other day I had to drive the car at 7am and the windows were all fogged, defroster didn’t do a thing, luckily once it got in the sun it cleared up. Just to be clear, I have the shop manual and vac/wiring diagram.

Here’s what I know -
-brand new compressor, charged and blows cold
-only blows on the feet
-firewall heater hoses are disconnected
-took a quick look behind the control panel, looks like there isn’t anything attached to control where the air flow goes
-when the compressor is connected and the a/c switch is on, it runs all the time and never shuts off


Here are some of the parts I have but are not installed-
-a/c thermostat
-new vacuum line kit (color-coded)
-water heater valve & hoses

I currently have the vacuum line disconnected from the carb but it normally runs from the carb to a vacuum reservoir (brand new) in the fender-well, then out of there to a vac port in the firewall, the other port from the firewall is what connects to the water valve if I am not mistaken.

Going to take this one step at a time, take things apart, put the new parts in and get it all connected. Am going to take pictures along the way to help others. Any advice is welcomed, needed, and much appreciated on where to start and what to look for!

First question, before I connect the firewall heater hoses, is there anything I need to look at for or do? My car currently looks like the picture this:
Hood Motor vehicle Car Automotive design Automotive exterior

hose goes straight from the manifold to the water pump, I need to get the water heater valve and hoses to the firewall connected.
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As an aside, your good looking engine compartment could be even tidier if you rotated your a/c comp. 90* clockwise. It would put your hoses on the side and under your mc bar. kip
Depending on the model of compressor they may have to be on top.
 

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I added factory AC to my 68. I had to search for all the original parts and restore them so I ended up doing extensive research on these systems, so I have lots of pics and documentation on them. I also spent a lot of time talking with Classic Auto Air about them.

From your pic, I can see the vacuum line going into the vac canister, but I can’t see it leaving. Might just be the pic. The hose should come from the back of the manifold on the vacuum tree to the vacuum canister. From the canister it goes through the firewall. If you have any vacuum accessories you might have a splitter with a check valve in it.
Check Valve - Headlight / Tilt Away Column Vacuum System - Repro ~ 1967 - 1970 Mercury Cougar / 1967 - 1973 Ford

The 68 canisters should have a check valve in it, but the repros I have used suck, so you might want to add an external check valve. Once through the firewall the line goes to a tee. One (Purple) line goes to the water valve vacuum switch, then back out the firewall to the water valve. The other line (Black) goes to the vacuum regulator (control switch). From the regulator you have red, white, and blue lines out to control the defrost, outside/recirculating, and A/C vs Heat door motors. There is also another tee in the red line and as it goes to 2 motors, 2nd hose is green.

The heater hoses are not needed for the AC system to work, but obviously you want them for the heater. The water valve needs to be checked for a vacuum leak though.

From your description, you have a vacuum problem. It could be the hoses, the tees, the check valve, motors, or the regulator. You need to track down the leak or leaks. I had at least one regulator, the simply didn’t work and wouldn’t send the vacuum to the right places. the tees are prone to breaking too. There is a nice little pamphlet on the system that will help you.

Wheel Tire Car Vehicle Hood


It has a diagnostic chart and lots of good illustrations.

The system does not have a low pressure cut off switch so you have to be careful not to run it when pressure is too low. (Or add a switch).

i would start by working from the manifold out, checking for vacuum at each point in the hoses to see when there is a leak.
 
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Looking good. You are on the right path. Looks like someone added a couple check valves (non Ford). You really only need one on the line out of the vacuum canister to the manifold. It keeps vacuum in the system when there is low manifold vacuum. One thing to watch out for, I have found a number of documents the have the vacuum lines drawn or labeled wrong Including the Electrical Assembly manual.
 

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You need to pull the box and rebuild it with new seals. Good chance the defroster duct door is bent or rusted up. You can repair the box with fiber glass resin.
 
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