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HVAC goes to floor/defrost while accelerating/cruising on Expressway

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    HVAC goes to floor/defrost while accelerating/cruising on Expressway

    Howdy folks.

    I read gadget's sticky before posting!

    Last night I noticed that if I did over 65 or so the HVAC would do what it's designed to do in failure mode: go to the mix position. I typically do 75-85mph whenever possible. It's probably been doing this but this was first time I drove car on the expressway in shorts, so I could feel the difference on my legs and then air flow out of the defrost register. Take my foot off gas to make more vacuum, all is normal. But, when I go back to 80 it goes back to the mix position shortly after. Is that just normal for 80 mph or extended acceleration? These things have no balls at that speed and my foot feels like it's at least halfway into the gas pedal so I can't imagine it's making much vacuum... I also noticed it this morning driving into work but that's probably because I'm aware there's a potential issue now.

    I want to know if it's normal for the system to do this before I start probing for problems. I want to say it isn't, but you guys know better than me. Within the last three weeks I replaced my TBL switch with a Motorcraft one and have been enjoying floor heat ever since. Before then I was just using the mix (floor/defrost) setting or the vent position. Never noticed any issues then. Also, I haven't been driving the car that much since I swapped over the switch, too much saltyness on the streets for my liking. Sticky says to check the switch, soup can, check valve or the line. I do have a vacuum pump and I suspect the TBL as that's what was changed recently. How do I test that, cover one of the nipples while trying to apply vacuum to the other?

    Thanks fellas,

    Derek
    1985 LTD Crown Victoria - SOLD
    1988 Town Car Signature - Current Party Barge

    #2
    Unless Town Cars are different the default, no vacuum, is all defrost. They need vacuum to move the air to vent and floor. I am not sure if you are saying the floor shuts off at higher speeds?
    03 Marauder DPB, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
    02 SL500 Silver Arrow
    08 TC Signature Limited, HID's Mods>235/55-17 Z rated BFG G-Force Comp-2 A/S Plus, Addco 1" rear Sway, Posi Carrier, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
    12 Escape Limited V6 AWD, 225/65R17 Vredestein Quatrac Pro, Winter 235/70-16 Conti Viking Contact7 Mods>Beamtech LED headlight bulbs, Husky floor liners

    Comment


      #3
      I thought default was the "Mix" position or where air flows through the defrost and floor vents. When there's sufficient vacuum, 95% of the air flow goes through the floor like I have it set to, however, extended hard acceleration or speeds above 70mph for longer than 10 seconds or so and you can feel the air speed decrease, the system begins to divert air through defrost and floor. Let off the gas and it's back to just the floor.
      1985 LTD Crown Victoria - SOLD
      1988 Town Car Signature - Current Party Barge

      Comment


        #4
        Well my experience is limited to the cv/gm's but this sounds like a very common problem.

        The first thing to check is the vacuum can. Does it hold air?

        Take time and look at each vac line under the hood, you might just see a crack.

        It is a very tedious process to check for these tiny leaks. After the can, I usually start by seeing if the leak is inside the car or in the engine compartment. If it is inside the car check the interior temp sensor first.

        The vac tree on the firewall is grand central for tracing these leaks. There is a least 1 one way vac valve near the tree that keeps the vac in the can, this is also a common failure point. The temp valve on the heater hose line is another failure area.

        It takes a little while to get used to the system.
        03 Marauder DPB, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
        02 SL500 Silver Arrow
        08 TC Signature Limited, HID's Mods>235/55-17 Z rated BFG G-Force Comp-2 A/S Plus, Addco 1" rear Sway, Posi Carrier, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
        12 Escape Limited V6 AWD, 225/65R17 Vredestein Quatrac Pro, Winter 235/70-16 Conti Viking Contact7 Mods>Beamtech LED headlight bulbs, Husky floor liners

        Comment


          #5
          How do you check the TBL? I think that's what it is. I recently replaced it and up until now I never noticed this before. I'll check the can and stuff this weekend along with the vacuum tree. Don't think there's a leak in the car as I don't hear any hissing. I'll get my "soapy woder" out and look for bubbles and such if need be.

          CV&GM would be same setup if they had the ATC option.
          1985 LTD Crown Victoria - SOLD
          1988 Town Car Signature - Current Party Barge

          Comment


            #6
            Since you recently replaced the TBL, check the vac lines to that thing and make sure you seated the vac connector all the way.

            Like Jay said, default should be full defrost. I'll second a vacuum issue as well but at the moment I can't think of any other advice beyond what was already suggested.
            Vic

            ~ 1989 MGM LS Colony Park - Large Marge
            ~ 1998 MGM LS - new DD
            ~ 1991 MGM LS "The Scab"
            ~ 1991 MGM GS "The Ice Car"

            Comment


              #7
              Word. It was seated all the way last I checked, I even put some dielectric grease on the rubber thingy to help make a better seal. Maybe rodents got to it or there is a leak within the TBL itself. How should I go about testing that?

              Also not sure if the thing does actually go to full defrost, it might but I'm pretty sure I still end up feeling some air going to my feet, majority being through the defrost. What position would require more vacuum to hold, Vent or Floor?

              Lastly, this isn't normal is it? You guys ever have problems with your HVAC holding it's setting at higher speeds?
              1985 LTD Crown Victoria - SOLD
              1988 Town Car Signature - Current Party Barge

              Comment


                #8
                TBL leak or the check valve at the firewall is bad. I've had this happen on both my beater and the Mark before I sold it.

                This is normal when vacuum drops out. But vacuum isn't supposed to drop out. Though with the front grill intake (redneck ram-air) on my beater, it drops vacuum below what can maintain the vacuum actuators when going over 60mph and the check valve allows the vacuum to bleed out after about 2-5 minutes and the vents drop to floor/defrost. I added a vacuum pump to augment that so it never drops below what it needs. I've also bypassed the TBL on that car.

                This is definitely normal for higher speeds up a hill as your foot will be down and manifold vacuum will probably drop almost to atmosphere. The system can hold a while when in good shape, but will still bleed out after a while. Hence the reason I added the vacuum pump so I wouldn't have to deal with tracing out all the vacuum fittings and re-sealing any that are leaking.

                Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                Originally posted by gadget73
                ... and it should all work like magic and unicorns and stuff.
                Originally posted by dmccaig
                Overhead, some poor bastards are flying in airplanes.

                Comment


                  #9
                  Its normal for it to shift when the vacuum drops, but its not normal for it to happen if something isn't wrong. Mine won't shift even driving up hills under heavy acceleration, though I did spend a lot of time fixing all of the vacuum leaks. None of them are air tight, but they will definitely hold vacuum for a long enough time that you won't notice it going stupid unless you're doing really unusual things.

                  I never had much luck with those TBL's. They leak internally. I'd unplug it and stuff a couple of ball bearings or other suitable plug into the vacuum lines to seal it off. Chances are fair that it will stop acting up. The check valve not quite checking or the can leaking are the other two common issues. Any of the rest of it can leak, but mostly its the stuff under the hood that is the big headache.
                  86 Lincoln Town Car (Galactica).
                  5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                  91 Lincoln Mark VII LSC grandpa spec white and cranberry

                  1984 Lincoln Continental TurboDiesel - rolls coal

                  Originally posted by phayzer5
                  I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                  Comment


                    #10
                    To check the tbl, remove the vac hose, attach another clean piece to the tbl and suck on it. While the hose is still in your mouth put your tongue over the end of the hose to make a seal. It should hold vacuum.

                    You can do the same thing with the check valve and then the can. This sucking thing is sort of the old fashioned vacuum pump.

                    I did go through leaks in two interior temp sensors in 14 years.
                    03 Marauder DPB, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
                    02 SL500 Silver Arrow
                    08 TC Signature Limited, HID's Mods>235/55-17 Z rated BFG G-Force Comp-2 A/S Plus, Addco 1" rear Sway, Posi Carrier, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
                    12 Escape Limited V6 AWD, 225/65R17 Vredestein Quatrac Pro, Winter 235/70-16 Conti Viking Contact7 Mods>Beamtech LED headlight bulbs, Husky floor liners

                    Comment


                      #11
                      yeah they seem to last maybe 10 years at a shot. The bad one in my car had an early 1990s date code on it when I replaced it in the mid 2000s. Its probably about due again, and I do not believe they are available any more. Next time it dies, if I can't get one I think it will be time for a conversion to manual controls. Probably just change the cable and fit a bracket onto the top of the blend door box.
                      86 Lincoln Town Car (Galactica).
                      5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                      91 Lincoln Mark VII LSC grandpa spec white and cranberry

                      1984 Lincoln Continental TurboDiesel - rolls coal

                      Originally posted by phayzer5
                      I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                      Comment


                        #12
                        Oddly enough, the TBL on my 88 still worked fine, but the rubber on the hoses going to it has degraded and the electrical connector was about gone, but the TBL itself was in good shape. I still tossed it though as it was original and there's no telling how much longer it would live.

                        Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
                        rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)
                        Originally posted by gadget73
                        ... and it should all work like magic and unicorns and stuff.
                        Originally posted by dmccaig
                        Overhead, some poor bastards are flying in airplanes.

                        Comment


                          #13
                          I ditched that thing a long time ago. The car had none when I got it. I did put one on it at some point, within a month it exploded and blew all of the coolant out of the engine. It went away forever at that point. It also had a vacuum leak from the moment it was installed, so that part got disconnected again. I was especially annoyed about that, those vacuum lines had been melted off some years prior and I actually spent the effort to splice new lines in from under the dash and feed them into the engine bay to make use of it.
                          Last edited by gadget73; 01-07-2017, 01:10 AM.
                          86 Lincoln Town Car (Galactica).
                          5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

                          91 Lincoln Mark VII LSC grandpa spec white and cranberry

                          1984 Lincoln Continental TurboDiesel - rolls coal

                          Originally posted by phayzer5
                          I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

                          Comment


                            #14
                            Pull vacuum lines off the TBL POS, plug them shut in any suitable way you can think of, go for a ride. If there are no issues holding vacuum then the TBL is indeed a POS in any shape or form (highly likely if it's a non-OEM part). If the issues do persist then the TBL is still a POS by design, but likely not the cause of the vacuum loss.

                            Personally I'd delete the whole mess once and for all. It has zero merit from day-to-day functionality stand point, and all it does is introduce potential (or already currently present) points of failure in both the HVAC and the cooling systems. Nix that shit, hid the vacuum lines, no one will ever know something ain't OEM-like. Cause fuck Ford and their "better ideas" and their ASSumption that ALL drivers are idiots that need constant baby-sitting.
                            The ones who accomplish true greatness, are the foolish who keep pressing onward.
                            The ones who accomplish nothing, are the wise who know when to quit.

                            Comment


                              #15
                              I just have to say I really like auto temp control. It is of course a level of complexity above manual controls and thus more of a PITA on old cars. I really like getting in and driving the car till the heat automatically comes on when the water temp is enough to make the air coming in warmer then the outside air. Also the fan speed being controlled by the inside temp is just great.

                              Between dodging people passing on the right shoulder, pedestrians "J" walking and generally looking where I am going while thinking how not to get boxed in and cut off, the auto climate is just set and forget.

                              The potential new wagon I have sitting around has manual controls and it bothers me. Yea I know it is very small, teeny tiny, in the grand scheme of life. After all who wants a car with options in it to foul everything up.
                              03 Marauder DPB, HS, 6disk, Organizer Mods> LED's in & Out, M&Z rear control arms, Oil deflector, U-Haul Trans Pan, Blue Fuzzy Dice
                              02 SL500 Silver Arrow
                              08 TC Signature Limited, HID's Mods>235/55-17 Z rated BFG G-Force Comp-2 A/S Plus, Addco 1" rear Sway, Posi Carrier, Compustar Remote Start, floor liners, trunk organizer, Two part Sun Visors, B&M Trans drain Plug, Winter=05 Mustang GT rims, Nokian Hakkapeliitta R-2 235/55-17
                              12 Escape Limited V6 AWD, 225/65R17 Vredestein Quatrac Pro, Winter 235/70-16 Conti Viking Contact7 Mods>Beamtech LED headlight bulbs, Husky floor liners

                              Comment

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