ACtion Magazine - June 2012 - (Page 28)

Diagnosis isn’t always as easy as looking up the symptoms in the computer. Trying to work out an unusual problem on a low-volume or seldom seen car often requires some extended thinking and experimentation. How do you do it when time is limited? by Richard McCuistian Running Short On Time and Info o troubleshoot an unfamiliar system, every wrench guy knows that we need three elements: First, we must understand basic principles; second, we need accurate information on hand for the vehicle system in question; and third, we need the time to apply the first two in gathering data to formulate a strategy and go through with a viable repair. If we come up short in any of those areas, the customer is usually disappointed and we tend to appear inept. Nobody wins in cases like this. The Jaguar owner waltzed up to my service desk with an HVAC problem that sounded extremely simple. Her air conditioner wasn’t cooling, but she didn’t have much time for us to look at it – she was only on campus for a short while, but how hard could it be? The repair order was written and the concern was verified – it was a hot day, and I had one of my sharp first-semester students start the car and dial the dual controls to their coldest setting. With my hand at the register nearest the driver window, I felt lukewarm air. I reached under the hood and felt the liquid line right by the high pressure charge port. That line was room temperature even with the compressor engaged. So the Neutronics identifier was yanked out, and we shut everything down to search for the low side port. Following the suction line (which was difficult) I couldn’t find the port under the hood, so I had Chelsea raise the Jag on the lift, and we found the port just inboard and behind the driver side front tire, pointing down. The identifier buzzed its way through calibration and showed we had 100 percent R-134a and nothing else. With the RRR unit connected we saw static pressures around 70 psi and with the A/C engaged they were running at about 38 on the low side and 175 on the high side. Those numbers seemed odd, so we decided to recover the juice and record its weight. Nothing was making any sense – after two recovery cycles (my machine is good, but it’s no J2788, so on balmy days, I do it twice) we got 2.25 pounds from the car, more than a half pound too much. I was thinking the pressures should have been higher 28 ACTION • June 2012 T since that was the case, but they weren’t. Somebody must have added some with a can and a hose trying to get things cool. A proper charge (1.7 lbs max) warmed up the liquid line (this alone was counter-intuitive) and chilled the suction line quite handily. But inside the car the leftcenter register was hovering around 70 while the rightcenter register was a toasty 100 degrees. Was this a blend door problem? No, because this car doesn’t use blend doors – it uses a split heater core with two inlets and one outlet, an electronically driven heater control valve with three hoses, three wires, and two solenoids, which is (in my opinion) a screwball way to handle cabin heat. From what I gleaned on Identifix from others who had blazed similar trails on this make, the problem was as likely to be the A/C control head as the heater control valve, but my rule of thumb has always been that the component that is in the most hostile environment doing the most difficult job is the part that fails. In this case, that would point toward the heater control valve, but how could we know for sure?

Table of Contents for the Digital Edition of ACtion Magazine - June 2012

ACtion Magazine - June 2012
Contents
Outlook
Expansive Valve
Technically RELAY-ted
Under the Southern Cross
Leonard's Law
Cooling Corner
Virtual View
News & Updates
State of the Art Detection
Running Short On Time and Info
The End of R-134A?
Association News
Quick Check
New Products & Services
Last Watch

ACtion Magazine - June 2012