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A/C is fast cycling but still cools only while driving

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    A/C is fast cycling but still cools only while driving

    Hey guys, I am trying to determine a problem with my A/C.

    While driving the A/C cools good. Not excellent but it does a pretty decent job. While at idle it hardly cools at all, I have to rev it up. When outside of the car I hear the clutch engaging every 3 seconds.

    I bought the car almost 2 yrs ago with 53k on it, I threw a can of DIY freon in it last summer. I assumed now I need a complete evacuate and recharge but the very fast cycling worries me a bit.

    I planned to take it in for an A/C system check ($20) and recharge ($90) tomorrow but if there is another problem like a relay or something, I would rather address that problem myself rather than pay someone else to do it.

    Suggestions? Thanks in advance!


    Also, is it true that you won't lose ANY refrigerant unless have a leak? IE-if your A/C is not cooling you must have a leak 'somewhere'.
    '01 Mercury Grand Marquis GS 4.6L
    '01 Ford Mustang GT 4.6L

    #2
    What year is your car? Does it have a condensor fan? Sounds like the condensor is not getting cooled properly and over heating in traffic. If it has a fan (like on my '95) see if it is working, not working or only sometimes. Mine had a short at the harness connector so I cut it out and reconnected the wires with connectors so I could later easily remove/replace the fan, if needed. If no fan, also check radiator and fan clutch.


    "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


      #3
      Sorry it's my '01 GM.
      '01 Mercury Grand Marquis GS 4.6L
      '01 Ford Mustang GT 4.6L

      Comment


        #4
        Like I said.....


        "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


          #5
          relay for the compressor must be working (it's cycling, after all).
          Like miamibob says: '01 will have an electric fan. Turn on the car with the a/c off, cold start. The cooling fan will not be on (because the car won't be hot). Now turn on the a/c. The electric cooling fan should immediately come on.

          The compressor cycles for a few reasons.
          I know for certain that it'll cycle when pressure is too low on the low side, which is a symptom of too little charge. So yes, too little charge will cause rapid cycling (pressure drops quickly because there's nothing there, clutch cycles off; cycles on, pressure drops quickly again: click, click, click, click...). There might be other causes for rapid cycling though.
          When you do an evac and recharge, (as opposed to just squirting in a can), they will be able to tell you how much they recovered. If they recover, for example, .2lbs... well, there's your problem. You were way too low.

          It's normal to loose say a tenth of a pound/year, ballpark. So a recharge every few years is nothing to worry about: you will never find that leak.
          If it's leaking rather faster, then they should be able to spot a leak. You use yellow tinted glasses and a blacklight. Check all the seams, wherever a pipe or hose bolts to a component or another pipe or hose, those o rings can leak; check the condenser for leaks; and check under the car by the evaporator drain tube.
          Or for their $20 checkup, they should be looking for these leaks.

          Comment


            #6
            *lose. apologies.

            Comment


              #7
              Theres a pressure problem, either its low, and dropping out because the low switch is cutting in and out, or its overcharged and the high pressure switch is cutting it in and out. You really need a set of manifold gauges to see whats going on.
              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


                #8
                I just put a can of R134a in my mom's vic earlier today. Compressor was cycling about every 5 seconds. Meh feeling air at idle. I put one can in and it nearly froze me out of the car. 104 degree day and the air coming out of the vents was 38 degrees. Woo

                Comment


                  #9
                  Cool thx guys.

                  I just went out and something weird (but good I guess) happened. I took an old gauge from a DIY can (can still attached to the gauge) and hook it up while the car was off and the pressure was around 100psi. I started the car and turned the AC on max (the electric fan started right up) and eventually the pressure dropped to about 45 which was just on the yellow (warning) & blue (fully charged) line. And the entire time the car idled, the AC was pretty darn cold (rather than being ambient). All lines were sweating and the clutch was not fast cycling anymore. Even after running for 5+ minutes full blast.

                  Not sure what that means but as long as it gets cold and isn't working overtime by fast cycling I gonna let it be. I'll keep an eye on it over the weekend.
                  '01 Mercury Grand Marquis GS 4.6L
                  '01 Ford Mustang GT 4.6L

                  Comment


                    #10
                    you might need to add a little. But also, keep in mind that if the car has been sitting in the sun, it will take 20-30 minutes to cool the interior on a 90+F day.

                    If it's been in the shade... 5 minutes tops. If it's an OLD system with R12 still in it... cut all numbers by 80% since R12 generally blows around 34-36ºF out the vents (at least on the ones I've measured) and with a good blower will freeze your ass PDQ.

                    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


                      #11
                      Rev the motor some. If the pressure drops off to under 25 psi or so, it may be low. Also keep in mind that the system is designed to cycle that compressor in order to keep the evaporator from freezing so some cycling is normal. It should not rapidly cycle though. Every few minutes is normal, every few seconds is not.
                      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
                        And the saga continues....

                        Friday the car did fine. Did not hardly cycle at all. Got cold almost immediately during idle. Pressure was no less than 45 I think (right on the line of fully charged and overcharged)

                        Then on Saturday it went to a fast cycle again, not cooling during idle, only during a slight rev of the motor. And at one time after I cut the car off, started it back up, then turn the max AC back on again, the AC compressor didnt cut on at all. (I started the car, cut the AC on, got out of the car and looked and saw the compressor not turning at all) Then again yesterday it went back to normal again. AC was cold at idle and got there quick.

                        Being that it gets cold immediately while running properly I believe the car does not need any additional charging. Could this be some type of switch/relay problem?
                        '01 Mercury Grand Marquis GS 4.6L
                        '01 Ford Mustang GT 4.6L

                        Comment


                          #13
                          Wiring short to Compressor or elsewhere???


                          "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


                            #14
                            loose connection on pressure sensors/compressor/relay?

                            corroded contacts on any of the above?

                            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


                              #15
                              the clutches on these can also need to be re-shimmed. The usual symptom is it won't engage unless you whack the compressor, or it simply engages or doesn't engage as it damn well pleases. Bad electrical connections or faulty high or low pressure switches, or a faulty AC WOT relay or compressor relay in the HVAC control head can also do the exact same thing.
                              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

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