Auto Air Conditioning & Heater Repair: 1994 Buick Park Avenue, buick park avenue, diagnostic charts

Question
The air conditioning will default to Econ without reason. Once it does, it can not be placed back on Auto. The system is charged and working fine. To reset it the battery has to be disconnected/re-connected. The air conditioning is factory of course.

Answer
Joel,

Right off the bat, I'd say there is an issue with the A/C Control Head (manual -C67), but that doesn't take into consideration that the (uplevel -C68) system has an HVAC Programmer that does all the work. Depending on your system, and the feedback you're getting from the control head (if any), that's where I would concentrate my diagnosis. The diagnostic charts can be a bit lengthy (sometimes they don't even have one, and you have to make up your own!), and the multimeter gets a good workout, but it should be pretty easy for a tech to track down. It's tempting to 'shotgun' a diagnostic, and just replace a control head or programmer, but bear in mind that most parts departments are sticklers about accepting returned electronic components.

Somewhat related, there is an issue (in TSB# 43-11-08) with the Blower fan feeding voltage back to the Control Head, but the symptoms are different than yours (starting out 'defrost' or 'defog' regardless of what it was when turned off). That's the only TSB close in a large list -- just for your information.

Good Luck!