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Sonic full of hot air

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By Brad Bergholdt

Published: Friday, Aug. 16, 2013, 9:07 p.m.

QUESTION: I bought a new Chevrolet Sonic last year. When I brought it in for the first service, I complained about the temperature of the fresh air. When the outside air is about 64-65 degrees, the fresh air coming out of the vents is noticeably warmer to the point that I need the air conditioner on and set for max cold. Then the exhaust air is moderately cool, not cold.

The service department wrote up a nice explanation of how the system works and said of course the air is warmer because the heater case is warmer. I complained that my last car — a 2004 Saturn, of similar size and shape — did not have this problem. They had me wait an hour, and then they told me they had looked at another 2012 Sonic and it also warmed the exhaust air when set for max cool. I told them that does not mean this is normal; that car just does the same thing.

Five thousand miles later, I again complained that I should not have to use the air conditioner on a mild day. This time I waited six hours before a mechanic said it's OK. When I asked if they could just show me the blend door, they said no — it would take 12 hours to pull the dashboard apart and they would not do that. I asked about contacting Chevy's regional troubleshooter to resolve this problem and they said no. Any advice?

— Stan Klezmer

Answer: Stan, it might help to take a series of precise temperature measurements with a digital cooking thermometer for comparison and further discussion. It's understandable the ventilation and A/C air discharge will be a few degrees warmer than the outside air. That's because of GM's temperature blend door method of regulating temperature, meaning the heater core continues to receive hot engine coolant at all times, and due to electronic devices behind the instrument panel radiating heat.

Your manual A/C Sonic uses old-school cables to link the control panel to the temperature blend and mode doors rather than more-techie and now common servomotors. If your ventilation air is more than about 4 or 5 degrees hotter than outside, it's possible the cable is misadjusted, misrouted, derailed or binding, or the door mechanism is simply not closing all the way, allowing unwanted airflow through the heater core. Another possibility is warm engine compartment air is entering the intake air grates at the base of the windshield because of a faulty or mispositioned cowl rubber seal.

Diagnosing warmer-than-desired A/C air discharge is tricky as there are many variables: ambient temperature, relative humidity, airflow across the condenser, refrigeration issues and the blend door. It's probably best to approach your concerns from the ventilation side, and assume A/C discharge would be identically affected.

GM Engineering has requested input on two occasions from servicing dealers regarding customer concerns of difficult operation of Sonic temperature and mode controls, and poor air conditioning performance. It's reasonable to assume these smart folks have or can come up with a solution to your concerns. I'd contact Chevy's customer service folks directly at: http://www.chevrolet.com/help/contact-us.html or800-222-1020.

Readers may send Brad Bergholdt email at under-the-hood@earthlink.net; he cannot make personal replies.

 

 
 


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