Heater not blowing warm air
This happened to my '06 3-series the other week. Started happening after coolant hose was replaced. New coolant was added but the system was not bled/flushed correctly (obviously I'm not a mechanic). Fix was super easy ... almost toooo easy???? Synopsys (sp):
Action that Caused Problem:
Coolant not added correctly.
Residual air in the coolant system.
b/c air in the coolant system, thermostat valve (valve controls the flow of cooolant to engine) remained in the open position (thermostat's job is to prohibit the flow of coolant to engine until engine reaches a certain temperature, at which time, it open the valve, allowing coolant to flow to engine.
Result of Problems: Coolant is constantly flowing to your engine thus not allowing your engine to warm up to the necessary temperature to deliver heat to the cabin of car. Also, makes your engine run very rich (eg, consume a lot of gas).
Note: (b/c we have different cars, you may have to improvise of modify a little but you should still be able to accomplish the same thing. My car has a square key hole adjacent to the steering column and a start button just above the key hole. To start the car (just a plain old regular start), key goes in key hole, step on brake pedal, and pressing the start button turns over the engine)
Insert key into keyhole. Do NOT step on brake pedal. Press start button. This will cause your climate control system to turn on but your engine stays off. Set your heater to maximum temp on both sides (mine's 84 or 86 degrees), turn fan to the lowest setting (but not off). Step on the gas pedal for exactly 10 seconds (pedal to the metal, baby). Release gas pedal after 10 seconds and let car sit it's current state for 15-20 minutes. Repeat once more if necessary. Completely shut down car (remove key, make sure climate control goes off, etc.) Hopefully car's thermostat/heating system is fixed and the car should be ready to drive immediately.
If this method fails to work but you still insist on having a warm cabin, there's one more fail-proof method: move to the desert (Phoenix, Palm Springs, Arabia, etc); accelerate in vehicle to moderate to high speed; roll down window. If cabin becomes to hot, take shirt off and discard out window.
Seriously though, I have know idea how the gas pedal/high temp, low fan trick worked, but it did.