Letters: Repair shop can’t find AC leak

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Updated: September 27, 2011 3:54PM

Q: I’ve had the air conditioning system in my Mercedes-Benz serviced and it doesn’t last for the entire summer. Last time it was inspected, a dye was added and the repair shop could not find a leak. What could be the cause of this? Can I put refrigerant in myself? What do you think? – Dave, e-mail

A: My first guess would be that the evaporator core is the source of your leak. That’s because the evaporator core is contained within a housing and isn’t as easy to inspect as the compressor, condenser or lines and hoses. For the refrigerant to leak out that quickly, the leak has to be fairly large. And if that’s the case it should be easy to identify.

One way to identify an evaporator core leak is to look for the presence of dye at the evaporator drain tube. Another way is to remove the blower motor resistor (or blower motor controller) to allow for a visual inspection of the evaporator core.

If the evaporator core is leaking, it’s a big, costly, repair. I wouldn’t recommend adding refrigerant to it as it will just leak out. And I wouldn’t recommend putting in that AC “stop leak” stuff they sell at the auto parts stores. The best way to stop a leak is to replace the leaky component or seal. I think you should find another repair facility and have them perform an inspection.

Q: In regard to oil change frequency you mention every three months or 3,000 miles. Does that rule apply for synthetic oil, too? – Alex, Bartlett

A: You probably could get away with extending oil change intervals when using synthetic oil, but I always recommend following the manufacturer’s recommendations. I looked at the maintenance guides for some high-performance sports cars that use synthetic oil from the factory and cars like the Corvette and Viper still call for 3,000-mile oil change intervals.

Q: Like many GMC Envoy owners, I have a low-beam headlamp that is out. The dealer is telling me it will cost about $1,300 to repair it. I noticed online that some are saying the HID headlamps can be eliminated by installing regular ones made for the same year S-15 Jimmy. Do you know anything about this? I’ve seen them priced as low as $100 for a pair. Do you know if they’ll work? – Ed, Oak Lawn

A: That’s one expensive headlamp. HIDs are great at providing better light, albeit, when they’re working. But unfortunately, they’re not as cheap to repair as halogen headlamps are. I spoke to Bob Cozza at All Guard Auto Alarms Inc. in Alsip. His facility repairs and installs a variety of electronic components including lighting systems. He said the price the dealer quoted you seems a bit high. Cozza explained that there are more affordable alternatives to fixing your headlamp. I’m not sure if the lighting units from another model will work in your Envoy. But I would recommend you get another opinion.

Questions for Ira Siegel? Call the Auto Advisor Hotline at (708) 633-6839 or e-mail autoadvisor.irasiegel@gmail.com. Siegel is an automotive instructor and an automotive service excellence-certified master auto technician.