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'87 GM A/C Issues

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    #1

    '87 GM A/C Issues

    The last few days I have noticed the following issues with the A/C:

    1) It is Auto Fan capable and even on a set speed, the fan speed raises and lowers.

    2) The Receiver/Dryer is barely cool and not "frosty" as it usually is.

    I was thinking the first issue was the fan switch, which I replaced. The connector, that many times is shorted "appears" ok. Only changed the switch but not the connector. Same problem so it didn't help. Could it be the Blower Resister?

    I checked the low pressure side and it is in the 40's. Don't have a high pressure gauge so I am limited. Also didn't take a reading of the inside temps. They feel "cool" but not "cold". Could there be vacuum issues? Perhaps the control unit has issues? Just throwing it out there to get some ideas.


    "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

    "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

    "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"
    Tags: None
    #2
    no clue about the fan speed thing when not on auto... but if the ambient air temperature sensor under the dash pad popped it's bimetal spring, it'll do stupid stuff. Also, if the main vacuum line to the controls is kinked, it'll do stupid stuff too. I'm guessing the compressor is cranking when you're measuring 40psi? If so, that should be the R134a happy spot for the low side.

    The only guess I have on the fan speed is either the resistor is starting to have issues (pull the connector off and check the leads for arcing burns) or the module that controls the fan speed is doing stupid stuff. But I have no clue where that is and it should be the same as my 88 and I've had that entire dash apart. There's nothing electrical on the blend door, so I have no clue where the hell they mount that thing to sense the blend door position or even how it does it or if it's part of the control module on the climate controls itself. (called blend door lever actuator in some parts lists) ATC is nice when it works... but a big PITA when it doesn't.

    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

      #3
      Compressor is running and the clutch is engaged. I'll have to peak at the blower resistor. I know I have changed it but that was back when dinosaurs roamed the earth! Also (around the same time) changed the ambient temp sensor which was a pain since it bolts "backwards".


      "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

      "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

      "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"

      Comment

        #4
        Then I'm betting on a vacuum issue or the controller in the switches.

        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

          #5
          Could be the parts we spoke of are bad (they have been in for a while). Will check the blower resistor first as it is the easiest to get to. Will have to wait, at least a few days, but will report back and still taking suggestions....

          P.S. It has the "slide switches" so who knows if the controller is at fault.


          "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

          "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

          "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"

          Comment

            #6
            Wonder what the best way is to narrow this thing down as opposed to merely changing the two mentioned parts? Took a quick look at the pin area of the resistor and di not see any burnt areas. Could still be bad but I don't know. Have to check the hose going into the ambient temp sensor to ensure there is no "funk" in there...


            "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

            "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

            "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"

            Comment

              #7
              Are the fan speeds changing or is it switching around (vent, floor, windshield) making it sound louder and softer?
              sigpic
              89 LTC 429>557 Cobrajet stroker
              13 F-150 XLT 6.2 l
              "If I could separate what's real from what I've been dreaming I could live to fight another day"

              Comment

                #8
                Appears to be fan speed changing. Good question, though, so will have to make sure! If it changes "location" it would probably be a vacuum issue.


                "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

                "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

                "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"

                Comment

                  #9
                  The fan speed changing in auto mode means the blend door is moving around. It runs at full speed towards the full hot or full cold ends of travel, and runs at low speed in the middle of the range. If you have the temperature set to full cold and its doing that, the interior air temperature sensor is probably bad and causing the blend door to wander around. It will also open and close the fresh air / recirc door as it moves off full hot or full cold, and it will tend to pick up noise and airflow in recirc mode.

                  Is the compressor running steady or cutting in and out? If its running steady but not blowing cold, that goes along with air temp sensor issues. If its cutting out, that may be low charge, but could also be blend door issues. Without enough airflow across the evaporator, such as when the air door is set towards hot, the system pressure will drop below the cutout pressure and it will cycle.

                  I'd fix the sensor issue and see what that gets you. It may well sort out all of the issues in one go. If you want to test the idea, unhook the blend door vacuum motor from it's supply line and apply vacuum to it directly. That will force the air door over to full cold, and should hold the fan speed steady as long as there are no leaks in the vacuum motor.

                  Vacuum leaks in the climate control system may also cause this. Loss of vacuum shifts air temperature to hot, and moves the air towards the defrost.
                  Last edited by gadget73; 05-14-2015, 06:27 PM.
                  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
                    The fan speed changes, up and down, while the switch is on a "non-Auto" position. So it occurs when on the top speed and everyone down to low. The compressor stays on and the car is "cool" but not cold. The receiver/dryer is barely cool but not cold as I am used to. Ambient temp sensor? As I said, I need to check the inlet hose to it to ensure there are no leaves or other items in it. I have the temp slider all the way to the left (lowest Cold setting).


                    "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

                    "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

                    "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"

                    Comment

                      #11
                      looks like you have the list... also, pay attention to when the speed changes... if it's when the engine is loaded, it could just be the vacuum dropping out and you'll need a new check valve.

                      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

                        #12
                        Originally posted by sly View Post
                        looks like you have the list... also, pay attention to when the speed changes... if it's when the engine is loaded, it could just be the vacuum dropping out and you'll need a new check valve.
                        You mean this "bad boy"??

                        Click image for larger version Name: 87 GM Check Valve.jpg Views: 1 Size: 13.4 KB ID: 1277501


                        "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

                        "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

                        "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"

                        Comment

                          #13
                          yup... that's the bastard. I have a spare one sitting on my desk just in case.

                          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

                            #14
                            Got a spare in my stash, as well. Do you remember where it is located? I would think near the intake perhaps on the driver's side???


                            "Hope and dignity are two things NO ONE can take away from you - you have to relinquish them on your own" Miamibob

                            "NEVER trade your passion for glory"!! Sal "the Bard" (Dear Old Dad!)

                            "Cars are for driving - PERIOD! I DON'T TEXT, TWEET OR TWERK!!!!"

                            Comment

                              #15
                              Passenger side (just) firewall on the vacuum tree.

                              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

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