wen u say it dosent work sufisiantly do you mean not enough flow of air or just not warm enough, if its low flow check the CABIN POLEN FILTER you can get from moste car shops its probley choked/dirty. if its not warm enough posibly the heater controle is jamed / damaged or the engin thermostat has failed open does the engin only warm up wen the car is stationary if so i wouild look toward the stat.
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