I have a 1981 corvette I put freon in it and 1 line is cold 1 line is hot contro l door is closing from hot to cold but will not cool.

sounds like you may have an over fueling problem. check for a leaking carb allowing fuel to run into the intake after shut down. have you checked to see if your missing spark when this happens. if not check if it could be a distributor component problem or coil.

Sometimes a temp problem like that is the ignition coil.
Hope this helps.

Well the blend door theory would work if the ac never got cold. But you say it starts out cold and then gets hot.
Its possible the system is freezing up due to lack of air flow thru the evaporator, or a blockage in the freon lines.
You would need to watch the high and low pressure gauge readings as the system gets warm.
You may need professional help for this.

u can get a deal that clamps on can with a r12 hose on it will poke hole in can put it in the low side

First of all get the Freon level checked, if Freon/ refrigerant is low then it can cause this problem.Wen Freon is low it takes time to cool.--- So first get Ac pressure tested.It can be tested at any local car garage.Some times pressure will be checked OK, but still if Freon is getting clogged in the line/ tube then it will not reach the front , but reaches rear then front will not cool, but rear will.--------

But mostly this problem is related to blend door.

If the rear is working well and front is not I would suspect a blend door or actuator issue in the front.Double check and see if you can hear anything moving when you are adjusting temperature from hot to cold.Also check and make sure the air flow moves properly from defrost to vents and floor etc.

Either a bad blend door motor or Climate Control Assembly. The A/C heater function selector switch combines a vacuum selector valve for direct control of the vacuum control motors and electrical input to the instrument cluster module.

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The blend door actuator is located behind the glove box.-----

To see blend door diagram for your Yukon Denail, click the link below :---

http://howtobyme.blogspot.com/2011/08/where-is-blend-door-actuator-located-on.html

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This will help.Thanks.Helpmech.

if full off freon. check system for a leak. that is the most logical solution to this problem.

Are you sure you checked the temp door ?Is it hot air ,like the heater?First check the ac compressor to see if it is actually turning,then check the large ac lines near the firewall near the windshield to see if they are cold,and sweating.If they are that rules out freon problem.The temp door might not be moving,check all selections on ac control and watch is door and see if one of them doesn`t move.If one door doesn`t move then it is the one you need to fix,if I can help,let me [email protected]

I Think I Can,
You Might Be Blending Hot Air With A/C Cold Air And Being 100Deg Outside, Your Getting
Really Warm/Hot Air Inside,
Your System Is Charged w/Freon, The A/C Compressor Is On/Engaged,
There Are 2-Aluminum Tubes Comming From The Compressor, [In & Out Pressure]
1 Tube Will Goto The Front Condensor, Infront Of The Raidator,
The OTHER Tube Comming Out Of The Condensor Will Goto A Dryer,
[Aluminum Looking Cylinder] Bigger Aluminum Tube[s]
The DRYER Will Then Feed Freon To Your Evap-Coil Inside Your Car [Cool-Air],

OK, The Dryer Tube's, 1 Of Them Should Be Cool/Cold, Locate That Tube, A Thermometer
wrapped w/Alum-Foil Around This Tube,
A/C ON, [A/C Compressor Engaged]
If You See The Temp Is Around 50-55 Degree's Or Lower, You Have Cold Air,
If Not, Above That, Low Freon, Or A restriction In The System. [Comes Later]
You Have Cold Air, You Have Warm/Hot Air Inside Car/Vents?
You Are Blending Hot Air w/Cold A/C Air, Problem Is With Heater-A/C Blend Box
Under Dash. There Are 2 Seperate Coils Under The Dash,
1 For Winter/Heat, Other [Evaporator Coil] For A/C, There Is a Diverter/Flapper door
That, For A/C, Closes Off The Heater Coil, Or It Should, To Prevent Engine Hot Water/Heat
From Blending w/ Cold A/C Air.
Most Are Controlled By A Diaphram, Vaccum Controlled From The Heater-A/C Controller
On The Dash.
If You Can Select From Defrost Vent To Dash and Floor Vents, Most Likely you Have
a Bad Diaphram That Controls The Heat-A/C Flapper Valve.
Most Time's You Can Open/Remove The Glove Box And See It,
A Temp Fix, For Cold Air, Would Be Remove The Vaccum Line From That Diaphram,
And Plug It, Pull The Metal Rod Back On The Diaphram with a Needle Nose Pliers,
If you Get Cold Air, Take a Ty-Wrap, Around The Shaft, Secure It, To Keep The
Vent In The Cold Air Position.
Then You Will Have To Get A New Diaphram Installed, Most Time's, Can Be Done
Through The Glove Box Opening.

Now About The Restriction In A System,
You Will Need A Set Of A/C Gauges, Car-Off, A/C Off, Connect Gauges.
IMPORTANT: The Gauges Before Connecting Should Show Pressure In Them [Freon]
Either The Gauges Have Freon In Them Or They Are In A Vaccum.
Otherwise They Have Air In Them, Air w/Freon=BAD Things.
OK, Gauges Show Pressure, Gauges Not Connected To Anything,
Open Up Both Knob's, Blue [Low-Side], Red [High-Side]
Gauges Needles will Move/Equal Out pressure,
BOTH Gauges Should Read Same Pressure, If Not, Quick Fix, Remove Gauge Glass
Covers, Need Little Screwdriver, If Gauges Off By ie: 4 psig,
Adjsut Low-Side [Blue] By 2psig and other, by 2psig, [Split The Difference]
So Now Both Gauges Read IDENTICAL Pressure.
Close Both Valves, Blue & Red
Connect Gauges To Car, Car=Off, A-C=Off
You Will See Pressure On Both Gauges,
Low Side Shuld Be Around 75-95psig, Depending on Outside Temp, If Around 60 or less
need freon.
OK, BOTH Gauges Should Show SAME Pressure reading,
If There Is MORE Than a 4psig Difference Between Them,
There Is A restriction In The System,
a Plugged "Orfice Tube" [Filter] Part Cost $3.00, Servicing The Filter, Alot More.
Restriction Causing Might Be , Moisture/Air in System [Improper Vaccum On System During Last Repairs], Compressor Breaking Down [Metal, Black Goo Bul-up]

Hope You Get Some Cold Air Soon.

tell me more how much did you put in the system? and did the compressor ever kick on ? the compressor is turned on and off by a pressure switch on your dryer .. when your full or at right level with your freon the compressor will kick on .. let me know if this helps any .. you might not have quite enough in there yet to turn on the compressor.. usually empty takes about 3 cans to fill the system.. thanks Jerry

Run the OBD diagnostic with the ATC self test feature. I bet you'll find a faulty blend door or motor....accordianman PS Three Pounds??!!?