Mark Houlahan
Tech Editor, Mustang Monthly
August 18, 2015
Photos By: Christian Arriero

As the summer months wind down and we reflect on how we only spotted a few vintage Mustangs out and about at shows and cruise-ins (here in the hot and sticky south anyway) it is easy to see that many owners are shy to bring their rides out when the mercury starts to rise. Blame it on global warming, or that today just about every home, office, and daily driver has air conditioning and we’re used to it, that the vintage Mustang stays in the garage because it’s “just too hot to drive it during the summer.” We can relate, as we’ve suffered through the sticky, sweaty legs on vinyl seats, no airflow from the cowl vents unless you’re moving (traffic jams are the worst!), and the feeling of being in a sauna when caught in an afternoon rain shower and you have to roll the windows up.

Thirty years ago the answer was finding an original A/C system and refurbishing it to use on your Mustang. Of course, the underdash evaporator wasn’t too difficult to find, and A/C hoses can easily be made, but it was the compressor, mounting brackets, additional drive pulleys, and more that often created the issue of getting a complete system up and running. Of course we’re really only talking about that option with the 1965-1968 Mustangs, as moving into 1969 everything was integral in the dash with really no room for a “hang-on” unit. For those lucky few who could find the stock parts a cool ride was their reward.

Today, thanks to companies like Classic Auto Air (CAA), upgrading your Mustang to the comfort of air conditioning means all new parts with modern electronic controls with full heat, A/C, and defrost functions and the efficiency of a modern rotary compressor. Best of all, when you order a complete system, like CAA’s Perfect Fit Elite we’re installing here, you get everything you need, right down to the pulleys, pre-crimped A/C hoses, wiring harnesses, and more for a true DIY installation just about anyone who can turn a screwdriver can handle. Check out this 1966 Mustang hardtop, as we update it with CAA’s Perfect Fit Elite to ensure the owner gets additional use out of it during those hot summer months.

01. The Mustang’s grille area will need to be disassembled for installation of the condenser, dryer, and some of the lines. This includes removal of the grille, hood latch and support, and the two horns.

02. The condenser is mounted to the Mustang via two pre-cut and bent mounting brackets attached top and bottom to the condenser. The instructions tell you exactly what screw holes to mount them in. The drier is attached to the side of the condenser. You can use the condenser’s liquid line as a gauge to determine drier positioning.

03. Install the liquid line between the bottom port of the condenser and the inlet to the drier. Use two wrenches on the fittings to prevent bending or damaging the drier or condenser. Don’t forget to install the high-pressure switch into the liquid line as well and connect its wiring pigtail to the switch now (easier than once the condenser is mounted in the car).

04. The Mustang’s core support will require two 1 3/8-inch holes to be drilled using a hole-saw. Factory core supports have two dimples where these holes need to be drilled, but if you have a replacement core support there’s a chance these dimples aren’t there to help you. In that case, use the A/C hoses/hard lines from the kit to determine proper hole placement.

05. Moving inside, remove the glovebox door, glovebox insert, radio, and ashtray to allow access for removal of the stock heater components. If your Mustang has a console it will need to be removed at this time as well.

06. The stock heater box is retained by these four nuts surrounding the blower motor at the firewall and one retaining bolt under the dash by the passenger side cowl opening. Drain the cooling system and disconnect or cut the heater hoses from the engine. Don’t forget to disconnect the blower wiring too.

07. Back inside, reach up under the dash and pull the heater box away from the firewall until the motor housing clears to lower the box to the floor. An old towel on the floor will help catch any coolant that drains from the heater hoses without damaging your carpet. Disconnect the resistor wiring connections and the three control cables and remove the heater box from the car.

08. The stock heat/defrost controls are retained by two opposing corner nuts on the 1965-1966 dash. Remove the controls, control cables, and blower switch wiring from the dash.

09. The CAA replacement blower switch mounts to the original dash controls with the included adapter bracket and attaching hardware. All of the control cables have been removed as well, since the Perfect Fit Elite uses modern electronic controls in their place.

10. The two cable integrators are installed onto the original dash controls, as shown here. These electronic slide controls replace the mechanical cables and allow the original mechanical controls to control the electronically actuated doors on the CAA assembly.

11. Remove the knobs from the original control panel and ensure the face is clean and free of grease or dirt. Affix the new control panel decal and then reinstall the knobs, rotated 180 degrees from their original orientation (lettering facing down instead of up).

12. Under the dash, this foam-sealed block-off plate is installed to cover the cowl vent opening, as it is no longer used with the new Perfect Fit Elite. The three tapping screws can be easily located for threading, as the plate comes pre-drilled with the screw hole locations.

13-14. The Perfect Fit Elite evaporator assembly is a semi-universal unit. These molded ducts are added on to make the evaporator more vehicle specific. The first duct is for the main underdash vents and the second duct is for the floor/defrost vents.

15-16. The Perfect Fit Elite utilizes color-coded wiring, which makes the wiring a breeze. Simply connect the blue harness to the motor with blue decal, yellow harness to motor with yellow decal, and so forth.

17. The same color-coding is found at the Perfect Fit Elite ECU. Plug the blue harness into the connector with blue decal around it. If you like, you can connect all electrical components on the bench and calibrate the system with the calibration key installed and using a 12V battery.

18. Using the included paper template from the instruction manual, locate and drill the 5/8-inch hole in the firewall that will allow the system’s drain hose to pass through to the outside. WARNING: There is a brake line mounted on the firewall very close to where this hole will be drilled. Unbolt the brake line retaining clips and relocate the line down a bit if needed.

19. The assembled evaporator unit with connected wiring harnesses can now be installed under the dash. Use a rotating motion to fit the unit up under the dash.

20. The unit is attached to the firewall with this one bolt. A helper positioning the unit and moving the unit as required to line up the unit with the factory firewall hole will be helpful in this one step.

21. Back inside the car there are two mounting brackets to support the unit under the dash. One bracket attaches to the original heater box mounting tab at the cowl vent opening (using a new J-nut and screw). The second mounting bracket is located on the evaporator unit next to the underdash vent duct and is attached to the underside of the cowl.

22. The updated dash controls can be reinstalled at this time and the blower switch connected to the new CAA wiring harness. The opposite end of this harness will connect at the blower motor. There are three ground wires to attach (one at the ECU, one at the blower motor, and one at the harness relay). The red/white stripe wire at the blower switch is your system power feed. Connect it to the original blower motor power feed wire under the dash.

23. In this particular installation the ECU was attached to the cowl vent block-off plate (be sure to use sealer on the screws) and the pre-connected colored wiring harnesses are plugged in. Note the orange harness isn’t plugged in yet. That’s because that harness is for the heater control valve, which will reside under the hood.

24. Slip the plastic line cover over the original blower motor opening, orienting it over the A/C and heater lines appropriately and then secure it to the firewall with the included tapping screws.

25. The original heater hose openings in the firewall will be sealed by these two plugs that are included in the CAA A/C system. Use a sharp knife to carefully place an X opening in the lower of the two plugs. This will be utilized for the heater control valve wiring.

26. We opted to grab some new heater hose from the local parts store to make the installation go easier and look cleaner. Following the labels on the heater control valve, cut the hose for installation of the valve in the upper heater hose and route the hose to the water pump fitting. Connect the wiring harness to the valve. The lower heater hose will attach to your intake manifold fitting.

27. Route the harness to the lower plug that was cut to allow the wiring to pass through and then route the harness under the dash to the mounting location of your ECU and plug it in.

28. While still under the hood, install the clear drain tube through the hole you drilled earlier in the firewall and ensure it is fully seated onto the drainpipe from the evaporator case.

29. The Perfect Fit Elite system includes new duct hoses, underdash ball vents, and defroster reducers and diffusers. Pre-assemble each duct hose onto the end of the reducer or ball vent and secure with the included tie wraps.

30. The defroster reducers allow the diffusers to attach easily. The diffusers are basically plastic versions of the original fiberboard diffusers and secure with the original spring clips. Route these two hoses to the defroster vents at the rear of the evaporator unit.

31. The underdash vents are attached to the forward lip of the dash with tapping screws. Place them evenly/as needed to clear the factory console (if equipped), parking brake handle, and so on. All four duct hoses will route to the four remaining openings on the evaporator unit.

32. Due to the size and mounting of the evaporator unit a revised glovebox insert is included in the kit. The insert attaches to the stock lower mounting points. Not shown here, but if you have a glovebox mounted hazard switch you can drill a hole in the back of the insert to mount the switch after taking the OEM metal bracket off of the switch. At this time you can reinstall the glovebox door, radio, and ashtray.

33. The factory crankshaft pulley is removed and is upgraded with the included kit pulley. Depending upon your fan/shroud and access you might need to remove these items for access. Often you can remove the crank pulley from the bottom without having to do so.

34. The A/C compressor mounting brackets attach to the driver side cylinder head and to the top of the water pump using new/longer fasteners. If you have factory power steering take note of the power steering bracket integration. Once all bolts are tight you can refill the cooling system now as well.

35. Mounted to the forward compressor bracket is this manual belt tensioner. The pulley and tensioner are shipped separate and must be assembled as shown. Leave the lower bolt finger tight for now until you install the belt.

36. Using the supplied spacers, mount the compressor to the two mounting brackets. Do not remove the line caps until you’re ready to install the hoses on the system. You can measure for the proper V-belt at this time too.

37. Installing the hoses is fairly straightforward, as their line size and length pretty much dictate where they go. This is the number 10 suction hose from the compressor’s suction port that routes around the rear of the engine to the large fitting passing through the firewall.

38. The short number 8 discharge hose from the condenser to the discharge port of the compressor is installed next. Shown here is the number 6 liquid hose, already connected to the drier, being routed behind the engine so that it can be attached to the small fitting passing through the firewall.

39. Here’s another shot of the number 6 liquid hose attached at the firewall. Use the included oil on all O-rings before making any line connections and also be sure to use two wrenches at all hose connections to prevent damaging hard lines.

40. The final bit of wiring is from the harness relay output (blue wire) to the pressure switch and then from the pressure switch to the compressor. Route the blue wire along the hose path behind the engine to the compressor area and connect it to one of the white wires from the pressure switch pigtail. Connect the remaining white wire to the compressor clutch wire. If you have the means, you can now vacuum the system and charge it, or take it to your favorite shop for charging.