By on May 14, 2012


TTAC commentator Kenzter writes:


I recently picked up a 1969 Cadillac Sedan Deville. It was one of those once-in-a-lifetime deals you only hear about, like my uncles cousins sister is selling her deceased husbands garage queen for pennies on the dollar deal.

My problem is, the Automatic Climate Control (a $550 option!) does not work. The only settings that trigger any response are FOG and ICE. Even then, I can only hear the blower motor and just barely feel air from the floor vents. Where to begin the troubleshooting?


Sajeev answers:

Damn son, that sounds like a choice cut of Cadillac. I love Caddy’s “fuselage era” not just because I bleed Panther Love, or started watching Mad Men from the beginning on DVD last week…but that never hurts!

First off, you told me absolutely nothing about the car’s condition.  Odds are older vehicles have worn out HVAC systems because of use or neglect.  I hope you understand the headaches associated with old car ownership: when I removed/replaced the evaporator/heater core/blower motor from my 1988 Mercury Cougar XR-7 with nearly 200,000 miles on the clock, I was horrified at the state of everything! But cleaning and replacing worked so well: even with a conversion to less-efficient R134a, the Cougar now has the strongest A/C in the Mehta fleet.  It will freeze the balls off a polar bear on the low-speed setting!

Even low mile garage queens have HVAC problems, because getting old is a bitch no matter who or what you are.

That said, my gut says you have bad vacuum lines under the hood. Especially the one from the vacuum source to the firewall, to (eventually) the HVAC box behind the dashboard.  But that’s for starters: I am so confident because you said the only “response” was from the defogger setting. Most, if not all, HVAC systems will default to the top setting when vacuum lines fail: this is a safety feature to keep your windshield from fogging up in interior/exterior climate changes. Well, in theory.

But what else do you do? You probably need a new blower motor, at this age. And maybe the factory service manuals (that you need to own) will help you dig deeper and find more problems.  Also get Cadillac specific parts catalogs from various vendors, just so you know what the world has to offer in terms of new parts.  Every catalog I get in the mail is like a mini-Christmas present…even if I may buy elsewhere, especially via eBay.

When you have the proper books, get the proper tools. Maybe join a local Cadillac-LaSalle club. Start reading up, learning and slowly tackle the project in your spare time.  Eventually you will fix the whole system. And enjoy the ride, because everything can and will eventually fail on an antique car. That’s part of the fun.

Welcome to the sickness, I am happy you joined us!

Send your queries to [email protected]. Spare no details and ask for a speedy resolution if you’re in a hurry.

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37 Comments on “Piston Slap: A Real Caddy, A Once in a Lifetime Deal…...”

  • avatar
    Mark MacInnis

    Kentzer: Get out, now, while you still can. Run!

    Find some other fool to drool over what this Caddie might never be….save yourself, your kid’s college fund, your sanity, your marriage or relationship…NOTHING this car is ever likely to be capable of again will ever be what it costs in time, money, relationships and emotional pain.

    The bitch will tease you, titillate you, promise to make you look and feel soooooooooooooooo good in her company, excite you, tantalize you. Cause you to fantasize being with her ALL THE TIME….

    And then she’ll take EVERY DOLLAR you have, and ultimately disappoint you, laugh at you and break your heart.

    You’ve been warned.


    Former (jilted) 1966 T-bird lover, only recently recovered my dignity, self-respect and credit-worthiness…

    • 0 avatar

      I disagree. Old cars aren’t ‘that’ expensive. My current girl friend came into the picture post project car. She knows it is a part of who I am (right now). It’s all about living within your means. Budget out your repairs, save and work on it yourself. People without passion are most likely sad, lonely and boring. If your passion is a car, enjoy it.

      My car will never be show car worthy, but it is road worthy, looks good at arms distance and I enjoy it.

    • 0 avatar

      Mark, having had a sister Wixom-built 1964 Continental in the family, I understand where you are coming from. The ’68 Caddy is not the same thing at all. By 1965, GM shared virtually everything, except engine internals, from Chevy to Cadillac. That includes vacuum operated HVAC systems.

    • 0 avatar

      As a former Jaguar owner, I have to agree with Mark. Now if you need a hobby and have plenty of time and money to invest, by all means go for it. Not my situation, unfortunately, so I had to let my baby go. Yesterday I drove by an XJ6 that looked exactly like mine, I couldn’t believe the emotion it brought out in me, I guess one never fully recovers. So unless you’re ready to commit, save yourself the heartache.

    • 0 avatar

      LOL Mark, thanks for the sage advice. My situation is a little different though, in that my partner loves the car as much as I do, and we do not have kids.

      • 0 avatar

        It’s good your partner loves the car as much as you do.

        Respectfully, any Jag, to me, is a good trade-in on something else. I’ve always understood most Jags and reliability to be mutually exclusive.

        I don’t know enough about the inner workings of ’66 T-Birds…as in how much under the skin did they share with a garden-variety ’66 Galaxie or Fairlane…to be able to comment.

        But as noted above, GM was doin’ a lot of systems sharing after 1965, plus this was the end of the era of Caddies that were actually built like Cadillacs should be built…those days have only returned recently as far as I’m concerned.

        Therefore repairs should not be as big a pain as they might be on other premium cars of that era.

        Get the factory shop manuals…not Chilton, not Haynes…not Motor’s, get the actual Helm manual Mr. Goodwrench used back in 1969. And if it doesn’t have radial tires…spring for a set. Amazing what a difference they make on those older cars.

        Good luck!

      • 0 avatar
        Educator(of teachers)Dan

        Worse comes to worse you could replace it with the control panel from an 1969 Impala with basic straight forward controls.

  • avatar

    If you are serious about keeping and driving this car, do two things.
    Go to ebay and see if you can get the workshop manual for the car. Should be available on CD if nothing else. Then join the Cadillac club

    They have a good forum and someone will probably know something. If you are lucky, you might just have a vacuum leak. If you are not, it might be one of the actuators leaking or broken. If you think the car might be too much for you to work on and maintain right now, there is also a for sale section in the Cadillac Forum.

    Climate control systems can be very difficult to diagnose. My advice is to get the rest of the car up to spec first. Timing chain, brakes, carbs, ignition system, syspension etc.

    Just switch off all the blowers and open the windows. Enjoy the car on a nice day. Then later once you know more about this car, try your hand at the HVAC.

  • avatar

    Actually, forget about everything else and do the timing chain and front bearings first. Many of these older cars had plastic (nylon) around the timing gear. They get worn out after years and having the timing chain jump or break is just a recipe for disaster.

    • 0 avatar

      Yup! I experienced timing chain sprocket failure on my ’77 Chevelle, fortunately it let go about 2 miles from my friend’s house and we towed it there to change it out. Supposedly made it quieter but I haven’t been able to tell much difference. It’s still quieter than the blower motor for the A/C.

  • avatar
    Felix Hoenikker

    My childhood neighbor and mentor died suddenly of a heart attack in 1988 leaving his pristine 1969 white Cadillac two door coupe to his wife who didn’t drive. It sat in the garage until 2001 when my brother convinced her to give it to him. But thirteen years of inactivity took its toll on the tires, suspension rubber, cooling and fuel systems. It took $3000 to turn back the clock and get it running again. But, it was magnicicant when finished. A year later he ended up selling it for $5000 to a collector.
    Not what I would have done, but he didn[t have space for it.

  • avatar

    Is this an 8 mpg Caddy?

    • 0 avatar
      bumpy ii

      Downhill with a tailwind. In those days, if you could afford to buy a Cadillac you probably had enough net worth to buy your own filling station.

      • 0 avatar
        Educator(of teachers)Dan

        Actually fuel economy was better before the primitive smog controls of the 70s. It really took Detroit 20 years to figure it out on that front. And remember when Jack Baruth drove the Talisman for the Mehta family he NEVER used full throttle. Think about that for a min, our barely tame race car driver NEVER USED FULL THROTTLE driving a classic Caddy across country!

        Besides sometimes auto ownership is about love not practicality.

  • avatar

    “because getting old is a bitch no matter who or what you are”

    words to live by

  • avatar
    Educator(of teachers)Dan

    BTW Kenzter, you are my new hero. Love some Detroit Iron.

  • avatar

    This climate control, though “automatic” was from before the age of the microprocessor. My mentor (long since retired) at a “large tier-1 GM electronics supplier” had actually worked on that system which he referred to as a “vacuum analog system”. The vac lines and actuator diaphrams would be the first place to start and work your way back from there. Switches and motors would be next, and then check wiring. The actual control system is probably an electromechanical gizmo with bimetal thermostatic springs linked on one end to the temp adjuster and the other end to a vacuum proporting valve. Think of the system as a “vacuum amplifier”. And good luck.

    • 0 avatar

      I would agree – the system is a complex system of vacuum hoses and actuators. At this age some of the hoses (all of them?) probably have hardened and cracked – no longer a reliable “conductor” of vacuum. At least it’s not the “hydraulic logic” of the transmission that is malfunctioning.

    • 0 avatar

      It’s probably very similar to the system GM used in the mid 70s, if so I’ve got some diagnostic charts to share with him.

      Most likely though it’s just bad underhood vacuum lines or a leaky brake booster. I ran into that with my 77 and it’s plain jane C60 4 seasons system, wouldn’t go into full MAX mode despite the lines being good, turned out the brake booster sprung a good vacuum leak.

  • avatar

    That looks like my dad’s Cadillac – except his was dark blue. Spare no expense!

  • avatar

    I dare you to paint that baby flat black and spray “Predator” in day-glo orange on the sides…

    Just joking. That would actually be kinda sacreligious.

  • avatar

    Thanks for responding! It’s in pretty good shape and has been driven regularly. The full story is on CurbSide Classics.¢-per-pound/

  • avatar

    I haven’t owned one of those Cadillacs, but I have owned Continentals from the same era. If the Cadillac climate control is similar, it is controlled by a combination of electrical switches and vacuum. Electric for fan speed selection and coolant temperature sensor, vacuum for air distribution flap settings and temperature modulation.

    Check all the vacuum lines, reservoirs, and check valves. Check the vacuum after the car has been turned off for a while–you can just tee in a vacuum gauge with the part of the vacuum system that feeds the climate control. If there is no residual vacuum after the car has been off for a while, you have a leak. A tight system should hold vacuum for days.

    The climate control heads also leak. I never had interest in repairing the head units myself, the are pretty complicated and marvels of what could be done with primitive technology. There were specialized services for Continentals that had an exchange program. Buy a rebuilt unit and return yours as a core. Surely someone is rebuilding the climate control units for GM products too.

    The first step if you intend to keep your classic car is to get access to the shop manuals. Your life will be much improved with a set of accurate troubleshooting charts, especially with all the accessories.

  • avatar

    I hate to break it to you but a lot of the a/c system probably needs to be replaced. The freon refrigerant carries a poly oil that lubricates the compressor as well as the o-rings in the fittings and when the a/c has not been run for awhile these bits dry up. The good news is that parts like hoses and o-rings can be replaced, the system recharged with new refrigerant, and you should be back in business.

    You can check to see if the a/c system is engaging by turning off the a/c, then looking at the pulley end of the a/c compressor; the outside of the pulley (where the belt groove is) should be turning but the center of the pulley (the clutch) should not be. Go back in the car and turn the a/c on; now the outside and inside of the pulley should be turning together(compressor clutch engaged).

    If both are turning the system is working; you may just have a bad blower fan (or relay) saving some real money. If the compressor is not engaging, not so good; the system is either out of freon and the leak has to be tracked down, repaired, and recharged or the system is not activating the clutch because of a control system problem.

    Hope that is helpful. Good luck.

  • avatar

    My advice? Bypass the original system with an aftermarket, universal solution for older cars like something from Vintage Air. It will save you a lot of aggravation and money.

    I had a similar “vacuum computer” system in my 1977 Cadillac Eldorado that I was able to restore. I rebuilt the system and luckily found an affordable NOS HVAC control box. The whole project though was a nightmare of chasing obscure parts and trying to make sense of a very convoluted system.

    No one would have complained had Cadillac simply put conventional controls for their AC instead of this Rube Goldberg mess of a system.

    • 0 avatar

      This. Having watched my father (who restores cars professionally) wrestle with the climate control (and related wiring/vacuum lines) on a ’66 T-bird and a friends ’64 Galaxie, the Vintage Air system (which he ended up installing in another client’s Model A) is definitely the least daunting. Vintage Air ain’t cheap, but it fixes the problem in a much more permanent way than tinkering with the factory unit ever will.

  • avatar

    Your system sounds like the one that Chevrolet refered to as “Comfortron”, I think it is basically the same, a fully automatic (not manual)HVAC system. I owned a ’66 Impala convertible with this system and they are very complicated and trouble prone.

    There is an A/C parts & repair place in Tampa, FL on Kennedy Blvd. “Old Car Air” or something to that extent and they can be helpful explaining these systems and providing parts (check Hemmings for the contact information). There are miles (slight exaggeration) of vacuum lines and leaks cause big problems but there is also a printed circuit on the control head and that can be the problem too. You need to get a shop manual, that will help explain some of it.

    One uninformed poster suggested using a basic control head from a Chevrolet; it will not work! The Comfortron based systems are considerably different. The refrigeration components and architecture are basically the same but the control componentry and design are very, very different.

    • 0 avatar
      Educator(of teachers)Dan

      Pardon me, I thought this was one place where the General’s obsession with standardizing as much as possible would give a benefit.

      • 0 avatar

        It actually did for the normal service life of the cars, ten years or so. All the replacement parts were available cheaply and techs everywhere could fix them because they were so common. In reality they worked very well for that first ten years. Vacuum hoses dry up and crack, as to the rubber diaphragms in the actuators.

      • 0 avatar

        The divisions were still fiercely independent in the 1960s, especially Cadillac. I would assume that this system (partly made by Delco in Kokomo, IN, and partly by Harrison radiator in Lockport, NY) is Cadillac-specific, even though it probably uses many of the same individual components (vacuum motors, etc).

        When I worked at Delco Electronics in the mid-1980s, Cadillac insisted upon their own, unique engine ECMs which had twice as many trouble codes as the ones used by every other GM division (who all shared the same ECMs with custom PROMs).

        If you buy an early 1980s Cadillac, expect to find it difficult to obtain a replacement engine ECM (it was getting hard to find good, rebuildable cores for the 1980-82 models even in 1986; Delco had nine regional repair centers around the country where ECMs were remanufactured).

  • avatar

    I fixed this issue once by replacing the control head. OR you can try to simply reseat the connections. If it works on FOG and ICE then I believe the control module or brain behind the glove is toast.
    I went thru the pain of replacing this item once and it worked for two weeks.. Was great while it lasted.. Good luck.

  • avatar

    This car is meant to be driven with the windows down. All of them.

  • avatar

    Let me begin by apologizing for nit-picking a seemingly minor point, but I must correct the reference to this car as a “fuselage era” Cadillac. The “fuselage era” began with the 1971 full-size models and ran through 1976.

    This car contains a design element so significant that’s its designer (Wayne Kady) is still remembered and credited for the concept. In 1965, Cadillac was shorn of its fins. Kady came up with the precise crease line in the side paneling that swept from the top of the front fender downwards across the body to the upper rear fender. This, combined with the rear fender “kick up”, visually gave Cadillac its fins back. These “phantom fins” first appeared on the 1967 full-size models (Eldorado excluded) and were a feature through the 1970 model year. Sorry, I had to give Wayne his props.

  • avatar

    Just be glad it isn’t an Imperial with the Autotemp system.

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