Intermittant A/C fault

Hi there. My 1999 6n polo has a wierd gault with ac opperation. When engine temp rises above 70 degrees the ac eill not pull clutch in, the switch illuminates but theres no volts at cluch plug on comp.
If ac is on at start up when cold it stays on.
Ive replaced the thermo swith in the thermostat housing and still the same.
Gas level in ac is good.
Anybody had similar issues. All help appreciated.
Gamba.

Hi again.
Anyone on here have any idea or k ow where i can get a wiring schematic for said vehicle?
Tia.
Gamba.

All sorted now. Thanks for all the replies and advice.