With all the electronic controls on today’s systems, it’s awfully easy to fall into the trap of looking for responses to them and letting those responses color our diagnostic thinking. The dual system on a 2003 Land Rover Discovery seemed to fit into that category. It switched from hot to cold and cold to hot nicely on the driver’s side, but seemed to be stuck in hot on the passenger’s side. So the technician started to think “electronic controls” and began digging into the HVAC case, first disconnecting the motor to see if he could hear any difference. He couldn’t, and he was next going to head for the heater, first hooking up the recovery machine so he could disconnect the evaporator, when another technician (who hadn’t settled into a particular line of thinking), said to do an evac and recharge. By this point, you’ve probably already figured out that the problem was just a low charge – about 12 ounces low on a 32-ounce system.
The “second opinion” is standard procedure for complex medical procedures. It’s always worthwhile getting one before you dig too deep into an automotive system unless the problem is very well defined. Much of the time during the heart of the A/C season, the shop is too busy to post the question at an online forum and wait for answers (although many technicians do, and are surprised at how fast many technicians respond). However, talk to another tech in the shop, another shop with which you have a friendly relationship, or look at a diagnostic chart or an on-line system like Identifix—just get that second opinion.
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Mobile A/C professionals should plan to attend 35th annual Mobile Air Conditioning Society (MACS) Worldwide Training Conference and Trade Show, Mobile A/C The Next Generation, February 11-13, 2016 at the Caribe Royale, Orlando, FL.