A/C’s not working; car chugs then stalls

Q: I have a 2009 Chrysler Sebring with 185,000 km. The air conditioning did not work last summer and I really do not need it. Is it important to have this working? I drive very seldom and only short trips. I am just concerned about it.

Ray

A: It isn’t important to have the air conditioning working unless you desire the comfort on hot days. Most of the time air conditioning stops working, it is because the refrigerant charge has leaked out of the system. The leak may be very small and occur over years. In this case, all your vehicle needs is to be checked for leaks and recharged. If the leak is measurable, then the system needs to be fixed before it can be charged.

When you operate the engine without the air conditioning working, the clutch on the A/C compressor does not engage. The compressor pulley is turning but it isn’t driving the compressor. The compressor pulley is acting like a big idler pulley. You don’t need to worry about belts or the compressor. Even when you select A/C on the interior control panel, the system won’t operate because low charge switches prevent the compressor from engaging, so keep the windows open and enjoy the fresh air.

Q: I own a 2004 Chevrolet Malibu that stalls when it is cold. It takes a couple blocks after starting before it stalls.

Then it chugs like it is starving for fuel or air. The check engine light comes on and a code sets for the mass air flow sensor. The light goes out after the car warms up.

Three mechanics, two air flow sensors, one computer chip, fuel filter, and injector clean later, I am out $1,500 and the car still stalls.

One mechanic checked for a manifold vacuum leak but couldn’t find one. Can you help?

A: There are a couple possible causes for your car’s stalling. A misadjusted minimum air setting causes the throttle plates to close too much and block off the engine’s air when you decelerate.

Normally, the idle air control valve controls idle speed, but it may not be able to react fast enough during a cold engine deceleration condition and the engine stalls. The throttle stop screw on these vehicles is not supposed to be adjusted but sometimes are by someone who is not familiar with fuel injection systems. Have the base setting for the throttle plates checked by monitoring the position readout of the idle air control valve when the engine is warm and idling. If the position of the valve is too high, then the throttle plates are likely open too far.

A sticking idle air control valve could also cause the stalling. Replacing it may be the answer. Finally, carbon deposits on the back of the engine intake valves could be the culprit. The carbon absorbs the fuel and the engine runs lean during cold start up.

Short of removing the heads and cleaning the valves, there is no other easy way to clean them. Some shops may use a walnut shell blaster (like a sand blaster) to clean valves, but this equipment is not common.

The mass air flow sensor code may be setting because of the uneven airflow through the sensor as the engine stalls. I am guessing the code is a symptom rather than the cause of your problems.