Auto Air Conditioning & Heater Repair: loss of heat, full size chevy, chevy van

Question
i have a friend that has a 1999 to 2001 full size chevy van that puts out veried levels of heat. he has replaced the thermostat with no change, the fan works and fuses are all good, what else could be the problem?

Answer
You need to be more SPECIFIC. Are you saying that the blower motor is not operating at full speed or are you saying that the air is NOT coming out of the correct vents or are you saying that you DO have full blower air coming out of the PROPER vents ?.

What was the last mechanical work that was performed on the vehicle of any kind ?.

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