Yup, if the heater core is plugged, it isn't going to give you good heat at high fan speed.

However, if it gets hot in defrost and not other modes, it's probably the PBCU, not the heater core. Hot water has to go through the core to get heat in defrost, too!

That doesn't mean the core is good, though -- if the outlet hose is still only warm in defrost, it's plugged, and it's a real pain to replace.


Peter

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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!