Could be the resistor pack, but I'd bet on brushes -- intermittant operation could easily be worn out brushes not making good contact.

The test is to check for voltage at the blower wires -- if you have voltage and the fan only operates sometimes, it's the fan. If the voltage comes and goes, it's probably the PBCU or fouled resistor pack.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!