AC compressor When I start my Envoy and the engine is cold, the air works great, but after drivng it for about 5 mins it quits. I started it up when it was cold and let it run with the air going for 30 mins. Air quit 5 mins down the road. took it in to get checked and they said the compressor wouldn't come on. Compressor works fine if the engine is cold. Should I just go ahead and replace the compressor or is it just something loose?

Who checked it ? Was it the dealer or a qualified repair shop ? You need to know how it works to test the system . Pressing the A/C button enables the HVAC control module to request A/C compressor engagement and turn ON the A/C button LED. The HVAC control module sends a class 2 message to the PCM for A/C compressor engagement. The PCM will provide a ground for the A/C compressor relay enabling it to close its internal contacts to send battery voltage to the A/C compressor clutch coil. The A/C compressor diode will prevent a voltage spike, resulting from the collapse of the magnetic field of the coil, from entering the vehicle electrical system when the compressor is disengaged. Defrost and Defog mode selections will request A/C operation but not turn ON the A/C LED.
The following conditions must be met in order for the A/C compressor clutch to turn ON:
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Ambient air temperature above 1?°C (35?°F).

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A/C low pressure switch signal circuit is grounded.

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A/C refrigerant pressure sensor parameter is less than 2413 kPa (350 psi).

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A/C compressor temperature switch contacts are closed.

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PCM receives an A/C request from the HVAC control module.

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Engine coolant temperature (ECT) is less than 123?°C (253?°F).

This all happens if the PCM sees the right voltage from low & high pressure switches . Plus the fact that you say the compressor comes on when cold, then shuts off 5 min. down the road . Just off the top of my head I'd say you have a pressure switch problem. Possible
A/C Refrigerant Pressure Sensor The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuits enable the sensor to operate. The A/C pressure signal can be between 0-5 volts. When the A/C refrigerant pressure is low, the signal value is near 0 volts. When the A/C refrigerant pressure is high, the signal value is near 5 volts. The PCM converts the voltage signal to a pressure value.
The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high pressure condition exists. The powertrain control module (PCM) disables the compressor clutch if the A/C pressure is more than 2413 kPa (350 psi). The clutch will be enabled after the pressure decreases to less than 1578 kPa (229 psi).
I would check it myself by finding the A/C compressor clutch relay in the under hood fuse / relay box an take a jumper wire an jump pin 87 & 30 sockets , where the relay plugs into the fuse box . If the clutch engages that part is good an there is a control problem ,not the compressor . If you pull the relay out of the fuse box an look on the bottom you should see four set of numbers , 87- 30 & 85 -86 .May have a fifth one 87a , don't worry about that one . There also be a diagram on the side of the relay . You can find videos on you tube testing relays . I would have it checked at another place too ,
I would