Only cooling one side

[SNSHN47]

I have a 2002 S60 Volvo. The air conditioner cools on the driver side all the time. But the passenger side blows cold and hot air intermitently. If I push and hold down the thermostat knob for the passenger side, it seems to start blowing cold air again but it doesn't last long. The clutch has been replaced recently but that was not the issue.