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1967-1971 Ford Thunderbird and 1969-1971 Continental Mark III
Air Conditioning Tune Up

Tips to make sure your factory air is a chilling experience!

It's that time of year again—when the dark, cloudy days and icy winds of winter turn into bright, sunny days and hot blasts of air—once again signaling the departure of winter and the arrival of summer. And with this change comes the desire for air conditioned air, and the concerns that accompany this comfort feature. Will it work? That's the thought that goes through many of our heads as we set the controls for cooling and flick the switch that is supposed to produce this wonderful manufactured air. Will it overheat? Is another thought that many of us may also consider, in recognition of the additional cooling challenges the use of air conditioning places on classic car cooling systems during the warmer months of the year.

Image: 1970 Ford Thunderbird 429 CID Thunder Jet V-8 EngineSince we're just dealing with tuning up the air conditioning here, we're going to focus on how to make a functioning system work better, and we'll assume that the basics, like refrigerant charge, is good, that your vacuum and electrical systems are functioning properly, and that there are no major issues with your car's cooling system. Major repairs of these systems are beyond the scope of this article, so we won't address them at this time.

One of the most important things to check on at least a couple of times a year is the condition of your cooling system hoses under the hood. These hoses are exposed to high temperatures and can be in need of replacement even though they look fine to the naked eye. Closely examine each hose, looking carefully for small cracks, especially at the ends where a hose clamp may be located. This is often one of the first places you can spot cracking or wear. If the hoses are older, you might be better off just replacing them so you don't have to worry about them. Sometimes loosening the clamp (cold engine only, please...) and pulling the hose off is the only way to check its condition. If the open end is showing cracks in the rubber, it's time for a new one. If there's any bulging around the clamp, that can also signal a weak spot.

Run your hands along each hose, squeezing them slightly to determine if there are any hard or soft spots. The presence of either indicates a hose past its prime. Replace it and you won't have to worry about it. Also look to make sure hoses aren't too close to exhaust manifolds, which can get hot enough to melt them. Check hose routing to make sure they are routed properly, too. Most shop manuals include a diagram indicating the proper routing of hoses. There is a reason the manufacturer placed them where they did; don't relocate them unless modifications specific to your particular car (such as a change of engine or other components) prevent them from being in original locations.

Check your fan clutch by spinning the fan blade by hand on a cold engine. You should feel some resistance, and the blade should only move a short distance before stopping. If there's no resistance or high resistance, or if the fan spins more than a quarter to half a turn, the clutch is likely bad and should be replaced. These cars should all have a fan shroud as well. If yours is missing, not only are you in danger of losing a finger but your car's cooling ability is greatly reduced as well. Even a cracked or broken shroud is better than nothing at all, so repair it the best you can and leave it on the car until you can find a better one to replace it with.The shroud concentrates the air flow through the radiator, and prevents air flow from moving around past the fan, which helps your car keep its cool under high ambient temperatures.

At this point, we're going to say you've checked everything under the hood, and it all looks OK, you've set the controls for cooling, and cool air is blowing out the instrument panel registers. You're at a good place. But perhaps the air flow doesn't feel quite as strong as your newer cars, and the air doesn't seem to be quite as cold, either. OK, there are a couple of things to check on. First of all...accept the fact that you aren't going to ever get the air volume out of your 1967-1971 Thunderbird air conditioning registers that you do in a newer car. Over the years, our standards have changed somewhat and today people expect to feel cold air instantly, whereas back when our cars were new people were a bit less demanding and impatient.

Given that your air volume won't be the same as a new car, let's check to make sure you're getting 100% of what was designed for your Thunderbird. With a cool engine, raise the hood and use a bright light to check the heater core/evaporator core housing mounted on the firewall on the passenger side of the car. Look for obvious cracks or missing pieces. Check to make sure all the screws holding it in place are there, and that they're tight. (Not too tight, these housings are old and can crack easily!)

Image: 1967 Thunderbird SelectAire Conditioner controlsIf all looks well with the housing, turn the ignition key to the accessory position (the engine must be off for this test), and turn the fan speed switch to the high setting. Go back around to the engine compartment and with your hands feel around the edges of the housing. Do you feel air blowing out? If you do, that's air that should be coming out inside the car, not out in the engine compartment! To fix, we recommend a product made by 3M called Strip Caulk. It's soft, doesn't harden, won't shrink, is waterproof, and is designed to fill seams, joints, gaps, and openings in body panels where a seal is needed, but when one of the panels might need to be removed at some point, so an adhesive isn't desirable. This caulk comes in 1 foot strips so it's easy to work with, and can be easily contoured to fit with your fingers. It can also be painted, if desired. We've found it handy for lots of things, and highly recommend it. Some auto parts stores carry it, or you can buy it by clicking this link: 3M Flexible Strip Caulk - 20 yds. total, 1 ft. lengths.

To use, simply insert the caulk into openings and smooth it out to provide a tight seal. Several pieces may be combined to fill larger gaps. Continue around the housing until you can no longer feel air escaping. It may be necessary to turn off the blower motor while making repairs, as the air pressure might force the caulk back out of the opening. Double or triple up the caulking in these areas, and force it into the opening, smoothing it out once the gap is filled. Be careful not to force so much in that it can interfere with the fan cage or air flow inside the housing.

Now get inside your car and with the blower motor still on high speed, shine a bright light up under the instrument panel so you can see the air plenum that directs the flow of air inside the car. Check for loose fittings, missing tape on the ducts going to the registers, and carefully feel for any air loss coming from the plenum or the ducts. Check the back side of the registers to make sure air isn't escaping back into the instrument panel. Ford issued a Technical Service Bulletin (TSB) on this for the early 1969 Thunderbirds. It seems the left air register was leaking air out behind the instrument panel, causing poor air flow from the register into the car. The fix for this is to remove the duct from the register assembly and use self-adhesive 1/4 x 3/8 inch polyurethane foam strip tape on the connection to seal it and prevent the air from escaping.

If you find any loose fittings, missing or loose duct tape, etc., correct and continue checking until no additional leaks are identified. Be sure to cycle the HVAC control to heat and defrost as well, and check to make sure you aren't losing air in any of those areas.

Once everything has been fixed, start up the car and check the air flow coming out of the registers again. Do you feel more air flow? Is it significantly stronger than before? It should be. Also check the ground at the firewall near the blower motor. It's on the engine compartment side. Clean it up and use a little Dielectric Grease to prevent corrosion.

For those of you with 1967 Thunderbirds, you should be aware that Ford issued a TSB on the air conditioning thermostatic switch located in the evaporator core. The original Technical Service Bulletin Number 73, dated August 11, 1967, outlined the step-by-step procedure to replace the switch, but identified the replacement part incorrectly. Instead of using the incorrect replacement part specified in the TSB (identified as C7SZ-19618-D), a later service replacement part was issued and is the only part that should be used. The new part carries part number C8SZ-19618-A. If your '67 still has the old C7SZ thermostatic switch, your cooling capacity is reduced and installing the updated switch should improve overall interior cooling.

With just these few checks, your air conditioning system is better prepared to keep you cool and comfortable on even the hottest days this summer.