April 14: Since I was fixing things, I decided to tackle another long-standing annoyance that had transformed into an issue over the last 9 years.

When I first test drove this car back in 2011, I encountered one instance where the air conditioning defaulted to the windshield while driving. This is an indication of a vacuum leak somewhere within the system. I didn't worry about it because it happened one time and didn't happen again for several more years.

All was well until last year when that annoyance started making its presence known more often. I also began experiencing a lack of airflow through the center vents. I did some digging and discovered one of the vacuum actuators within the system was leaking, (i.e. no longer holding vacuum). Like just about everything for this car, the part was obsolete and no longer available. I was able to find one used from a Jaguar parts specialist and installed it last summer. The system would now hold vacuum, but the defaulting issue was still there.

Since I currently have the time, I figured that now was as good a time as any to take a more in depth look at this problem. My first step was to borrow a coworker's "smoke machine." This is a diagnostic tool that detects leaks in non-liquid systems, (like a vacuum system). To my surprise, the smoke machine revealed no external leaks. But it did reveal a check valve that wasn't working which explained the defaulting concern.

But the airflow concern was still there. Now it was time to investigate further which required tearing things apart. Access to the main vacuum harness is behind the center console trim. I removed the lower trim shields so I could examine the connector.

Several vacuum lines are present, but not easily seen in the photo above. The main vacuum supply for the HVAC system is supplied via a white line. A blue line supplies vacuum to the recirculation door which is part of the blower motor housing. A red line supplies vacuum to the heater control valve under the hood. A green line controls the operation of the defrost vents. And a black line controls the center dash vents.

The white connector in the bottom center of the photo above is a for the red and white vacuum lines. I checked this connector and found it good and working properly.

Moving to the driver's side of the car, I removed several shields and trim pieces to access the vacuum control switch, (the black piece with four ports). This switch is basically the brains for the vacuum part of the system.

The red connector seen in the photo above plugs into the vacuum control switch. Four vacuum line colors I mentioned earlier can be seen, (red, green, black, and blue). The fifth line, (the white supply line), connects to the back of the switch.

My limited understanding of how this system works is that the white vacuum line supplies vacuum to the switch. The switch diverts that vacuum to the appropriate line depending on what is being called for, (i.e. a/c, heat, or defrost). This means a malfunctioning switch could be the cause of this whole problem. That would be wonderful because I wouldn't have to remove the dash to get to any of the inner components.