I have a horrible smell coming out of the vents of my '09 Corvette whenever I use the air conditioning or heater. The smell seems to get better after I drive the car for awhile (or maybe I just get immune to the odor). My daughter Samantha was home for a few weeks in the summer. She asked me to take her car to the service station to fill it up with gas, and I noticed the same smell coming from her air conditioning. She drives an '07 Chevy Cobalt. Is it just me, or is there a problem with the A/C systems on GM products?
Via the Internet
You're correct: GM has received a lot of complaints about musty odors coming from the heating, ventilation, and air-conditioning (HVAC) systems of its newer vehicles at start-up, especially in hot, humid climates.
It's possible that the odor is the result of microbial growth on the evaporator core.When you turn on the blower-motor fan, the microbial growth releases a musty odor into the passenger compartment. This condition could be caused by condensation build-up on the evaporator core. This condensation can't evaporate naturally in high-humidity conditions. Other potential sources of the odor include a stopped-up HVAC drain tube, which can also cause microbial growth.
Remember: if there's any way for water to enter the vehicle and get into the carpet, that could also cause a musty odor to develop. Some of the culprits here include a leaking heater core, torn weather stripping, or a poorly sealed window.
If you determine the carpet isn't wet, and the HVAC tube isn't stopped up, the odor is most likely caused by microbes on the evaporator core. Fortunately there's a technical service bulletin (TSB # 99-01-39-004C) covering a repair procedure for this problem. It covers all '93-10 GM passenger cars and trucks.
The repair procedure includes the following:
•Diagnostics to confirm that the A/C drain tube is not restricted
•Visual inspection-and, if necessary, replacement-of the cabin air filter
•Applying a cooling-coil coating to the evaporator-core surfaces
•If needed, installation of an Electronic Evaporator Dryer Module Kit (PN 12497910 or A/C Delco 15-5876)
This repair is a time-consuming and complicated job, so it's recommended that you have it done by a GM-certified technician. If you decide to attempt this operation yourself, be sure to get a copy of the TSB and follow the step-by-step procedure. Here's to the sweet smell of success.
Oil-Change Intervals Revisited
I've had more feedback on this topic than any other I've written about. It seems there are a lot of conflicting opinions on when to change the oil in your Corvette, most of them having to do with the onboard engine-oil-life monitoring system and the durability of synthetic oils.
Since 1990, Corvettes have been equipped with an oil-life-monitoring computer that records the number of engine starts and revolutions, coolant and oil temperatures, and other data to help determine when the oil should be changed. Once the computer has determined that the oil's life has been exhausted, it will illuminate a "Change Oil" light in the instrument-panel cluster (IPC). The system can't, however, analyze the oil-it can only make an educated guess at its condition by measuring trends in engine operation.
On newer Corvettes, the "Change Oil" lamp will typically illuminate at between 3,000 and 10,000 miles after the previous oil change. In cases of severe duty, it may come on before 3,000, but it will never come on at more than 10,000, which is the maximum oil-change interval allowed by GM for the LS engine. (Remember: This monitoring system must be reset after each oil change.)