98 blows hot air

[UpInSmoke]

all the time!
The speed adjustment works fine, but will not blow cold/warm, only full hot all the time!
Where should I start to diagnose this issue?

Thanks!!

[CajunSpike]

Have the a/c coolant pressure checked to see if you have any. If a leak developed and you lost the r134, it won't get cold.

Also, the mk1's have a heater control valve which lets hot water flow past even when its closed, when it fails. Not sure if mk3's have same type valve..probably so. If thats bad...won't cut off hot engine water and will always have hot air out the a/c system.