If you are talking about your Nitro, Chrysler uses an electronic mixing valve, to control the temperature entering the cabin. There is a small electronic motor that moves this valve, via a plastic gear. Sometimes the motor fails, and sometimes the plastic gears can strip. If you turn your control valve from cold to hot, or hot to cold, and you hear clicking, the gears are probably stripped, not allowing the valve to mix. If you turn the heater fan down, you should be able to hear the motor - it should be on the passenger side, behind the glove box. At least, that is where it was on my Jeep. Good luck.
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2011 Nitro Heat 4x4:
Bright Silver Metallic,
Dark Slate Gray; Customer Preferred Package 24C; Trailer Tow Group; Hood-to-Fender Stripes; Navus 2; Uconnect.
MODS: S/S Nerf Bars;
Mopar Chrome Rear License Plate Brow, Chrome Exterior Package, Production Style Cross Bars, Deluxe Molded Splash Guards, Cargo Security Cover, Door Sills & 3.7L Emblem; Media Center 230; Kicker Speakers; Carbon Fiber Dash Kit.
FUTURE MODS:
Mopar CAI, Pedal Kit; Heated Katzkin Leather.