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  1. #1
    Member damoroso's Avatar
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    Default Need A/C help in Florida

    I'm outta ideas, I hope someone out there can help. I have a stock 81 with about 65K miles on it that I bought in January (This is my second 81, I've had a 65 and a 67 as well). I can't get the a/c to get any colder than 66 going down the road with the a/c on max.

    Here's the story. A few months ago, the a/c wasn't getting as cold as is should have so I replaced the hotwater shut off valve, as that seems to be a part that fails fairly often and it's not very expensive. That didn't work.

    I took the car to an a/c "expert" and he informed me I needed a new compressor. It was original and was making alot of noise, so I agreed and decided to change over to R134 at that time. He replaced the compressor and the dryer/accumulator. Then just a couple of weeks ago I took it back to him and he replaced the clutch fan. Still the sytem only got down to the mid sixties. He tried several times and told me that's as cold as it gets, because this is an old car.

    Next. The next "expert" I brought the car to this last week, re-wired the electric fan so it comes on any time the ingnition is on, telling me that moving air across the condenser would fix the problem. At least that's what he told me when I picked the car up. Nope. Still the best it'll cool is 66.

    I've check all the vacuum valves, the outside air, and vent, are working as they're supposed to, I've seen them. They also seem to be sealing. The duct work under the dash is intact, and the hotwater valve is getting 20+ inches of vacuum when it's supposed to close.

    I'm outta ideas and it's freakin hot here in Florida!!!!!
    Anyone got any ideas?!?!?

  2. #2
    Member gmjunkie's Avatar
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    Quote Originally Posted by damoroso View Post
    I'm outta ideas, I hope someone out there can help. I have a stock 81 with about 65K miles on it that I bought in January (This is my second 81, I've had a 65 and a 67 as well). I can't get the a/c to get any colder than 66 going down the road with the a/c on max.

    Here's the story. A few months ago, the a/c wasn't getting as cold as is should have so I replaced the hotwater shut off valve, as that seems to be a part that fails fairly often and it's not very expensive. That didn't work.

    I took the car to an a/c "expert" and he informed me I needed a new compressor. It was original and was making alot of noise, so I agreed and decided to change over to R134 at that time. He replaced the compressor and the dryer/accumulator. Then just a couple of weeks ago I took it back to him and he replaced the clutch fan. Still the sytem only got down to the mid sixties. He tried several times and told me that's as cold as it gets, because this is an old car.

    Next. The next "expert" I brought the car to this last week, re-wired the electric fan so it comes on any time the ingnition is on, telling me that moving air across the condenser would fix the problem. At least that's what he told me when I picked the car up. Nope. Still the best it'll cool is 66.

    I've check all the vacuum valves, the outside air, and vent, are working as they're supposed to, I've seen them. They also seem to be sealing. The duct work under the dash is intact, and the hotwater valve is getting 20+ inches of vacuum when it's supposed to close.

    I'm outta ideas and it's freakin hot here in Florida!!!!!
    Anyone got any ideas?!?!?
    It needs a FORD "Blue" orifice tube and Exactly 10 % less 134a than the original R-12 charge!!I retro fitted my 78 15 years ago when I had to replace the evaporator!! It'll still freeze the KaHoonies off a Brass Monkey!!
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


  3. #3
    Member damoroso's Avatar
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    THANKS!! I was completely outta ideas, at least that gives me something to try! I'll let you know what happens....

  4. #4
    Member gmjunkie's Avatar
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    Quote Originally Posted by damoroso View Post
    THANKS!! I was completely outta ideas, at least that gives me something to try! I'll let you know what happens....
    You can get the orifice tube at just about any parts store!!It's allot better if the 134a is weighed in,there is only a 2 oz window with 134a,It's not as forgiving as R12!! If its 1 oz overcharged or 1 oz undercharged the system won't work properly!!
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


  5. #5
    Member minifridge1138's Avatar
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    What is the orifice tube you're talking about?

    My AC is also only cooling to about the mid-60's.

  6. #6
    Member gmjunkie's Avatar
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    Quote Originally Posted by minifridge1138 View Post
    What is the orifice tube you're talking about?

    My AC is also only cooling to about the mid-60's.
    The orifice tube on a C3 is located in the inlet of the evaporator at the end of the high pressure line!(small line!!) Thats where liquid Refrigerant changes to gas!!134a expands at a little different rate than R12,so to be optimum the system needs a different size orifice and less refrigerant!! Go's in the long end as Liquid,comes out the small end and turns to Gas!!! Thats where the cooling comes in!!

    White StockGM ...............................................................Ford "Blue"



    P.S. Your low side pressure switch should be set to disengage the compressor at 21-22 psi!!Other wise,freeze up can occur!!
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


  7. #7
    Member minifridge1138's Avatar
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    How do you set the low pressure switch?

  8. #8
    Member navy2kcoupe's Avatar
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    Junk, I also heard that if you convert to R-134a, the system won't get as cold as with the R12 because (and here's where the memory starts freezing up) either the evaporator or the condensor should be larger for the R-134a, and I don't remember which one. Kind of a moot point anyway because there ain't no room for a bigger one of either in there.
    Andy
    Andy Anderson - PROUD VIETNAM VETERAN.

    Vietnam Veterans Corvette Club - Founding Member #1

    "Dream as if you'll live forever...........Live as though you'll die today" - James Dean

    "Money isn't everything.........but it SURE DOES keep the kids in touch!"


  9. #9
    Member gmjunkie's Avatar
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    Quote Originally Posted by minifridge1138 View Post
    How do you set the low pressure switch?
    Unplug the connector on the switch,right between the 2 spade connectors there should be a small screw,Turning the screw Counterclockwise will lower the cycle off pressure,Clockwise will raise the cycle off pressure!! "Helpful Hint" If the ambient temp is too high,the low side pressure will not drop to the point where the compressor clutch will disengage.If this happens,disconnect the blower motor.The reduced air flow will enable the pressure to drop below the cycle off pressure!! (This can help the technician check the cycle off pressure of the switch!!) If 21 psi cannot be obtained,replacement of switch will be necessary!!
    PS. 1/8th turn = approximate 1 1/2 lb

    Quote Originally Posted by navy2kcoupe View Post
    Junk, I also heard that if you convert to R-134a, the system won't get as cold as with the R12 because (and here's where the memory starts freezing up) either the evaporator or the condensor should be larger for the R-134a, and I don't remember which one. Kind of a moot point anyway because there ain't no room for a bigger one of either in there.
    Andy
    Maybe Andy!!I know that on a Hot day a 134a system takes a minute or two longer to start Kicking than R12, But if I follow my "Guide to Retrofitting" to the T,You CAN hang Meat in Them!!
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


  10. #10
    Member damoroso's Avatar
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    Thanks for all the help, we're getting there!!

    I had the orifice tube changed and the charge put in @ 90% of what the R12 called for. The system is down to about 53 in the car now and the low side is @ 26 psi (I'll check the cycle pressure of the switch tomorrow) with the high side at 235 - 240. What we checked next was the evaporator temp. Pulled the resistor block outta the housing and using a infra red temp gauge found the evap to be at 36 degrees, so the system seems to be working pretty well. Then we checked the housing temp itself and found it to be about 180 where it faces the engine, which has to heat the air around the evap. I've got to believe that has some impact on the temp of the air getting inside the car, so I ordered a 12"X12" piece of KoolMat that I'll put on tomorrow. It's not there yet, but it is getting better!!

  11. #11
    Member minifridge1138's Avatar
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    What is the correct psi for the low and high side?

    You say pull the connection and the screw is between the spades. This is the electrical connection going to the compressor?

  12. #12
    Member gmjunkie's Avatar
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    Quote Originally Posted by minifridge1138 View Post
    What is the correct psi for the low and high side?

    You say pull the connection and the screw is between the spades. This is the electrical connection going to the compressor?
    No, It's the 2 wire connector on the Low Pressure switch!! This switch will be somewhere on the low pressure side of the system!! Usually it's located on the Accumulator (Receiver Drier) or on the Large line coming out of the Accumulator!! (See Photos below,screw is between the spades on the switch!!) This is on my hauling truck,but is the same type system,My 78 and 81 are in Storage right now!!

    PS. Be sure that the Gages and Hoses are Pre Charged,Otherwise you WILL end up with a Under Charged System!!
    "If its over 1 oz overcharged or over 1 oz undercharged the system won't work properly"!!
    Gage Set can hold from 3-6 oz depending the length of the hoses!!

    There is no Pre Set High side pressure,High side pressure is determined on Ambient Temp and will usually run between 145-350 PSI!! More than that and you probly have a restriction in the high side!!(Lines,Condenser or Plugged Orifice tube!!) or Overcharged system!!

    Low side should run between 22-32 PSI!! With Compressor cut off set at 21 Lb!!

    "Helpful Hint" If the ambient temp is too high,the low side pressure will not drop to the point where the compressor clutch will disengage.If this happens,disconnect the blower motor.The reduced air flow will enable the pressure to drop below the cycle off pressure!! (This can help the technician check the cycle off pressure of the switch!!) If 21 psi cannot be obtained,replacement of switch will be necessary!!
    PS. 1/8th turn = approximate 1 1/2 lb







    Most switches have a regular Screw Slot,this one is a Aftermarket and is Bass Ackwards and requires a Special Tool or Needle Nosed Pliers!!
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


  13. #13
    Member minifridge1138's Avatar
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    The low pressure starts at about 26 psi and goes up to about 30 psi as the engine warms up (i assume the engine heat causes the gas/liquid to warm up and expand).

    The compressor never shuts off. It runs the entire time.

    The AC blows air that is about 65 degrees.

    What is the proper compressor shutoff adjustment procedure?

  14. #14
    Member gmjunkie's Avatar
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    Quote Originally Posted by minifridge1138 View Post
    The low pressure starts at about 26 psi and goes up to about 30 psi as the engine warms up (i assume the engine heat causes the gas/liquid to warm up and expand).

    The compressor never shuts off. It runs the entire time.

    The AC blows air that is about 65 degrees.

    What is the proper compressor shutoff adjustment procedure?
    You can't get there from where your at,You have other problems!! Over Charged,Under Charged,Too much oil in system,Improper Orifice Tube,Bad Accumulator Drier,Bad Fan Clutch,Bug's in Condenser,The low side pressure should go the other way, Down, Not Up as it's running!!

    Answer these questions,and I'll try to Help you Narrow it down!!

    1.Whats the low side pressure do if you unplug the blower motor??
    2.What is the High side pressure??
    3.What is the Ambient Temp??
    4.What is the engine Idle RPM??
    5.What is the engine Temp??
    It's got so it seems to me that the Internet has created a lot more Horses A$$'s than we have Horses!
    junk!~!!
    Founding Member: 10 Corvettes Anonymous


  15. #15
    Member minifridge1138's Avatar
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    Quote Originally Posted by gmjunkie View Post
    1.Whats the low side pressure do if you unplug the blower motor??
    2.What is the High side pressure??
    3.What is the Ambient Temp??
    4.What is the engine Idle RPM??
    5.What is the engine Temp??
    1) How do I unplug the blower motor? Pull the fuse or find the connector in the engine compartment?
    2) about 250 psi
    3) about 90 degrees
    4) 700 RPM
    5) 185

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