Once in a great while someone will inquire about putting AC in a Mustang II. Having just completed a second installation of a factory AC unit I thought I’d pass on some of my experiences with them.

This information is for the FACTORY set up. I have seen pictures of one dealer installed set up. Although it does not look to be quite as efficient as the factory installed setup (smaller evaporator and only 2 dash mount AC vents) it would also appear to be a MUCH easier installation if you can find a complete one.

First off let me say that done properly, this is not a simple or cheap project. Besides installing the under the dash unit, control panel, compressor and condenser, you will also have to change the under dash wiring harness. At a minimum, you should plan on new AC hoses, new receiver dryer, new heater core, and new heater hoses. The good news is, if you are capable of changing a heater core and water pump, chances are you are going to be able to install AC in your car (the under dash unit has to come out to change the heater core, and the AC compressor is bolted to the water pump). If you are planning on having a shop do the work for you, expect to spend some big bucks!! I run a garage, and based on the time to do the installation, labor would run about $1000. Parts could easily run another $1000 depending on how cheap you can acquire the AC unit for.

Before removing any AC components insure the system has been properly discharged. Once installed the system will need to be evacuated and properly charged. UNLESS YOU HAVE THE PROPER TRAINING AND EQUIPTMENT TO DO THIS, LEAVE THIS PART OF THE JOB TO A PROFESSIONAL.

You first order of business will be to acquire the parts to do the conversion. I have seen AC units occasionally offered at swap meets and on E Bay, but to date have never seen a COMPLETE one offered. Ideally you should find a donor car of the same year/ engine size as the car you planning on putting the AC in (you may find it’s actually cheaper to buy the whole car than just the parts).

MAKE SURE YOU GET ALL THE PARTS YOU NEED!!!!
For this swap, you will need the following parts:

• Under the dash unit
• Under the dash wiring harness (and possibly ignition switch)
• Glove compartment liner (it’s different on AC cars to clear the blower)
• Driver and pass side dash face
• Heater/AC control panel
• Vent delete plate (located on driver’s side inside firewall up near dash approximately 4"X 6" plate held on with 2 screws)
• All ducting
• The vacuum fitting off the intake manifold
• Vacuum reserve can (located under the plastic splash shield inside the passenger side front fender)
• Expansion valve (bolted to the evaporator pipes on the engine side of the firewall)
• Accumulator /muffler (located on the tire side of the pass side inner fender well)
• Condenser and brackets
• Water control valve (located in one of the heater hoses, it has a vacuum line going to it)
• Receiver Dryer (location varies depending on engine size)
• Compressor and brackets
• All the AC hoses
• Body plugs (located on the firewall that are used to plug the holes not used when AC is installed)
• Ambient Temp Switch (the photo cell looking thing located in the center of the grill attached to the hood latch brackets).

If you cannot find a car of the same year group as yours, or if it has a different engine size, it will still be possible to use some of the parts for this swap. (I used mostly parts from a V6 car in my wife’s 77 Cobra V8 Cobra II). The under the dash units are the same from 74-75 regardless of engine size and any of those will work. The rub comes in the dash and wiring harness.

The 74 dash and wiring is by itself as the wipers are dash mounted instead of mounted on the turn signals as the 75-78s are.

The 75-6 wiring harness is slightly different from the 77-8 harness in that the ignition switch and plug are different. They can be interchanged as long as the correct switch for the harness is used. The other minor problem you may run into is the Tach plug. The 4, 6 and 8 cylinder cars all used a unique plug for the Tach, (the wiring is the same so all that will be required is to change the plug if you are using a harness from a car with a different size engine).

The under the hood wiring harness does not have to be changed, as the only circuit that is goes out there is for the compressor (it goes through the ambient temp switch and has a lead off of it for the fast idle solenoid) but these are easier to add if not already there, than to go through the trouble of changing the under hood wiring.

The compressor brackets are unique to the different engine sizes, regardless of year and must be for the engine that your car has. The Ford compressors themselves are the same and will fit whatever brackets you are using. If you can’t find a Mustang II with the same size engine for the brackets and pulleys don’t despair, as brackets from an early to mid 70’s 302 powered fords will work for the V8 cars. If you have to use brackets from a full size car, make sure it has a 302 and NOT a 351W, as the 351 brackets do not fit. Pinto brackets should interchange for the 6 and 4 cylinder cars.

The condensers, receiver dryers, and accumulators are also unique to the different engine sizes. If you run into a bind on these parts, you can do what I did and use a universal condenser (I used a 23" X 14") and a universal receiver dryer and delete the accumulator.

Once you have all the parts, the next order of business is to check them/refurbish them. As you probably know by now removing the under the dash unit is a major job. I highly recommend that you replace the heater core at this time you don’t want to take the chance of getting the unit all back together and charged only to find you have to take it apart again in 6 moths to replace a 30 year old leaking heater core. Prior to installing the unit I also check the wiring harness, blower and switch unit and vacuum doors. This was rather simple I connected the wiring harness as it should to the switch and AC unit. I applied power to the fuse box at the AC fuse, and grounded it through the little black wire with the eye terminal that connects to the ash tray bracket. For the vacuum motors, you can apply vacuum through the engine vacuum hose with either a vacuum pump or if your up to it my just sucking on the hose. Run the switch through all the positions and make sure all the vacuum doors operate properly.

Finally remember that the cooling system will have an added load on it, and should be in optimum shape. It might not be a bad time to have the radiator checked or replaced to insure the car will not overheat when the AC is used. A fan shroud will be required and if you can find a fan with more blades than what you have so much the better.

All that’s left at this point is installing the unit. Take your time and don’t force anything, remember, the factory did it and so can you.

©1998-2014 The Mustang II Organization, ©1997-2010 D'TechnoArt Designs, & ©1999-2014 Lee Lafountain