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My heater/ac ducting isn't working 700 1989

The vents aren't working on the heater/ac ducting. I tried tracing the vacuum lines but aren't able to find any tears or other damage. The car has
Heater control With manual ac control. Any suggestions?










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    My heater/ac ducting isn't working 700 1989

    I forgot to ask, did you start with the basics to make sure you have vacuum to the servos? Even though the odds are very high you'll find a leaking servo, you will normally still be able to hear a bit of hissing or movement at one of the servos when you operate the heater vent control. You'll want the engine running and maybe blip the throttle to generate extra vacuum (unless a turbo with a vacuum pump). As needed, check that the engine is capable of generating vacuum by pulling the booster hose nipple after running the engine to hear the vacuum released. Verify that the check valve on the firewall that's a couple feet up the vacuum line is working, that the line to it isn't plugged and that there's no damaged or melted vacuum line on the engine compartment side.
    --
    Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now








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    My heater/ac ducting isn't working 700 1989

    Almost guaranteed it's one or more failed pneumatic servo actuators. There are three of them on the left side of the main air distribution box in the centre console. With vacuum shunted through the heater control panel switch, they open and close the vent shutters. It's the internal diaphragm that fails. The inability to hold vacuum in one servo can affect the others. It's an extremely common problem, but not an easy repair, especially as the Volvo parts are no longer available. The middle one has two vacuum lines to it and it's the one that seems to most often fail, leastwise it's the one that most often causes noticeable problems. There is a relatively simple bypass you can do blocking off the lines to restore partial functionality. Once you've got the left console side panel off, it's usually fairly easy to figure which one is leaking by attaching a length of plastic hose to each nipple and applying suction by mouth. You can access some of the hose connections without removing the side panel. Most people just do the bypass and learn to live with reduced functionality. There's all kinds of good info here in the 700/900 FAQ on both the bypass and doing a proper repair with substitute parts. There have been additional posts in more recent years here in the RWD forum with more tips and suggestions of other substitute parts. You'll have to try searching for them.
    --
    Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now








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      My heater/ac ducting isn't working 700 1989

      Thanks for the dose of reality. I was hoping for a miracle fix without having to deal with the vacuum motors. Which is worse? Working with these things or changing the fan motor on a 140/240. Both suck.








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        My heater/ac ducting isn't working 700 1989

        Hmmm, tough question, Bob. It's been a lot of years since I tore into my 140 dash (same as a 240) to work on a horridly chirping blower that was headed towards a seizure. The skinned knuckles have since healed and the flashbacks have stopped. I've since done two 700/900 heater cores, a similar PITA job regarded by many as worse than the blower motor. I wrote up the procedure for the FAQ as therapy to avoid PTSD.

        If you've never torn very far into your dash then I would call replacing a servo motor an onerous task for some people. For such people, my heater core writeup has step-by-step details on how to tear into the dash and even get to and remove the front section of the distribution box for full access to the shutters and levers. For me, I have yet to replace a servo in any of my 700/900s, but have had to do the bypass in all of them. It's a matter of time and priority. If I was ever faced with a heater core again then I would definitely make an effort to source suitable servos and do a proper replacement. I could probably do it in my sleep after all the times I've been under the dash for one reason or another. My back is quite used to all the contortions.

        I'd recommend starting with a bypass and decide later if you want to waste another day trying to do the servos to get a bit more air.
        --
        Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now







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