I have an 02 Disco SE with the automatic climate control and I have a weird issue with the AC.
When I turn the car on, the AC starts to cool and works well but if I drive 10-15 min warm air starts coming out of the vents.
This happens if the system is in Auto or I manually adjust it.
Also, the passenger side blows warm all the time, even if it is set to 60 or LO while the drivers blows cold air. I pulled out the glove box and did see the blend doors moving when I adjusted the temp but I still think there is an issue with the heater core note being fully blocked off. I'll have to dig into the second issue further but what has me baffled is the issue with the AC slowly starting to warm up after driving a while. The system is charged and the pressures between high and low are in spec when the compressor kicks on (I have a buddy with an AC machine that checked this out last weekend). I also checked for faults but did not see any in the HVAC control panel.

Any suggestions?

 

Put the HVAC controller in to diagnostic mode and monitor the evap temp sensor. If it is faulty it will eithher turn off the compressor or run it continuously and freeze over the evaporator.

 

If your drain tubes are clogged / and its filling up with water, it can cause this condition. Give them a chk

 

Thank you for the suggestions, I will give both of those a try and see what happens.