By on December 13, 2019

1988 Lincoln Town Car Rear, Images: © 2017 Sajeev Mehta

Peter writes:

I got a case of Panther Love and bought a nice 89 Town car. It’s a lower mileage (62k) girl, one that has been taken care of. I DD it.

I have been busy fixing everything that breaks on it. Previous owners just didn’t use her much, and so a wide variety of stuff just goes out. Window regulators. Alternator, battery, alignment, tires…… the list goes in and on. Every week something happens. That’s ok, and I expected as much. The engine, body, interior and tranny all seem good-superb.

It has of course an automatic temp control HVAC system, and and already I have been chasing numerous gremlins. Started with needing a new heater control valve as the floor setting never worked for the heater. That was an easy fix. But now it seems she has vacuum leaks under the dash or in places my good mechanics can’t find under the hood. Leaks that cause the system to do weird stuff, like sending all the air to the defroster under acceleration, and or switching from Heat to ac and back just for a moment. They have run all sorts of vacuum tests under the hood and can’t find the problem.

My questions is this: I have very good vintage car mechanics, but they charge 140/hour and it adds up quickly. And they are not HVAC specialists. They will gladly troubleshoot if I let them. Pull the dash and start poking around. That’s the next step.

Is there not a better way? Does an Ford (or any manufacturer) Vintage HVAC mechanic exist somewhere, someone who already knows the system? Seems to me that the experience curve might be mighty handy here. Something like a Lincoln doctor who is board certified in HVAC. That would be too cool. I can dream, no?

Or should I just stick with the guys I have and hope for the best while paying the man. I live in the Washington DC metro area. I am obviously not capable of doing this myself.

Sajeev answers:

You could find a retired Ford tech willing to help via Craigslist wanted ad. Only one way to find out!

I suspect you’ll find a simple repair once you look inside the dash: having disassembled multiple 30+ year old Fords (including an ’88 Town Car) I have little fear, but anyone with plastic trim prying tools, patience and common sense can do this in a matter of hours. I bet the main problem is a vacuum leak (i.e. going to defrost at low vacuum/full throttle) from the hard plastic hose going through the firewall and back into the engine compartment.

Or maybe you’ll get lucky and a smartphone based inspection camera finds the problem after removing the glove box?

I reckon you’re in the same situation as a previous Piston Slap query: a vintage auto tech needs to loosen/remove the dash, inspect and learn by doing. Honestly, it’s a simple system (as far as automatic climate control affairs go) and this is a good time to install a new heater core and clean/replace the A/C evaporator too: as time goes by both will need attention.

If you want to save some cash, take apart the basic bits on the dash yourself: the fake wood, stereo, glove box, dash top, kick panels (the dash normally bolts to the body behind them) before taking it to your mechanic. Buy a factory shop manual for any 86-89 Town Car on eBay for cheap if you need an exploded diagram for reference. It will come in handy for plenty of things in the future!

Since this is your daily driver, this is also a good time to replace all the T-10 bulbs with a bulk order of natural white LED lights (eBay, amazon, etc) to keep the wiring healthier (i.e. not bake) and reduce the load on your battery. Ask me how I know.

[Image: © 2017 Sajeev Mehta/TTAC]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice. 

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17 Comments on “Piston Slap: HVAC Heartaches Beset Panther Love?...”

  • avatar

    I used to work on these- there’s supposed to be a check valve between the vacuum source and the system. It’s under the hood and looks like a fuel filter for a lawn mower. They are frequently removed by mistake and they do fail occasionally. When there’s no vacuum, the system defaults to defrost.

    • 0 avatar

      I am going to second this – start from the source and work your way in. Had the same issue on something much older but same symptoms. There was a hairline crack on the nipple for the vac line going into the firewall.
      Vac gauge didn’t catch it so on a whim I moved it a known good source and problem solved. Do what you must to avoid tearing a 30 yr old dash apart – to fix one prob you get 100 more..

  • avatar

    I’ve had an ’87 and two ’89s as my DD (before moving on to newer model LTCs), and on my ’87 this happened. Most of the independent shops I use have a few older guys that are used to working on these, so you should be able to find someone relatively easily. On my ’87, I recall it was a part behind the glovebox area (there are two, one is the HVAC Mode Door Actuator, and the other is a Defrost mode door) that they replaced. This was back in the mid-’90’s and was about $100 for the parts. Sounds like your problem likely is one of these bad boys.

  • avatar

    I had a similar problem with my wife’s vintage Mustang many years ago. It turned out to be a rusted out vacuum reservoir which provides vacuum for the system when accelerating and there is little or no manifold vacuum. The mechanic should check for vacuum at the A/C function selector valve. A road test which includes WOT would be best.

  • avatar

    You’re lucky it’s still at an age where most controls are done with cables, linkages and levers and can be improvised with a little ingenuity and or similar parts donated from junk cars, trucks or farm/yard equipment. And for very little cash.

    Today’s gadgets for days and 200+ processor controlled cars are another story.

    • 0 avatar

      It’s for the same reason I always advise people to stick with vacuum tube and relay based computers instead of these junk solid-state things. Can’t just swap out a tube to fix your fancy non-serviceable CPU, now, can you? I didn’t think so!

      • 0 avatar

        Nice! All’s fine as long as they know what they’re buying. The point is cars are getting as disposable as electronics.

        That’s not a bad thing necessarily, and many would say it’s a worthwhile “trade off”, as long as they know what they’re getting themselves in to, top trim, luxury, etc, especially. Volvo, Alfa, Mercedes, BMW, Maserati, etc, double especially. They should come with a disposal fee.

      • 0 avatar

        Peak electronics = the 555 timer.

        Sajeev, your articles are costing me money and I don’t even own a Panther! (Just ordered a set of shop manuals [on CD-ROM] for my ’95 CK as there is an AC evaporator replacement in my future – have put it off long enough.)

        • 0 avatar

          It won’t be long until they’ll just drive themselves to the nearest contracted junk yard at the end of the lease and a new one just shows up, unless you cancel (in time).

          • 0 avatar

            There is a running joke in Japan about the “Sony timer” where the product stops working just after the warranty ends.


      • 0 avatar
        Art Vandelay

        “these junk solid-state things.”

        LOL…My Pioneer SX-1980 Amplifier My Dad got new in like 1979 and will still rattle the house courtesey of Eddie Van Halen begs to differ.

        Automotive circuitry of this sort is not complicated. I have run some of that stuff on hardware far less powerful than a Raspberry Pi in my job.

        • 0 avatar

          To be fair ;

          I too have some 1960’s & 1970’s Japanese radios that soldier on well yet I’ve also had Japanese electronic products that were shoddy and didn’t last even with careful use .


  • avatar

    Vacuum controls are only as good as the hoses, and vintage cars like this boat look like a spaghetti plate under the hood. Would companies like GM and Ford spec lower-grade hoses to save a nickel, hoses that last 5 years instead of 25? You bet they did, and owners reap the whirlwind when they start failing. Good luck with your “project” car — it’s like a box of chocolates…

  • avatar

    As Sajeev & others mentioned, it’s 90 + % certain a vacuum leak issue .

    Begin by finding out where the vacuum check valve is supposed to be and test it ~ I highly recommend a ‘Mity-Vac’ tool Harbor Fright sells then and a cheaper one that invariably leaks vacuum making it worthless for this typ of work .

    30 years of thermal cycles and hydrocarbons floating under the hood means none of the original vacuum hoses are any good ~ grab one and pull ~ if it comes off without a vigorous twist, it’s bad and is leaking .

    Find out what size inner diameter hoes you need and go buy a 25 foot roll of it and replace each and every hose one at a time (!) you’ll be amazed at how much faster and better the plenum doors will change position .

    The Mity-Vac tool can be used to test the various vacuum diaphragms too, they must all hold vacuum indefinitely .

    Often just replacing all those damned hoses will make the system work O.K. even with a leaky diaphragm .


  • avatar

    What you want is a place that specializes in emissions repairs. They will be able to find the leak quickly with their smoke machine. Usually it is used to find vacuum leaks in the EVAP system but it will find other vacuum leaks too. Or you can look on youtube and there a number of people who will show you how to make your own smoke machine for cheap.

  • avatar

    I probably miss Sajeev’s Town Car more than he does.

    Such a lovely color combo.

  • avatar

    I bought this endoscope in August as a cool toy, and it’s already saved a friend from hours of teardown on a bulldozer.

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