One problem after another with Mercury
(MCT) -- QUESTION: I have a 2008 Mercury Grand Marquis with 51,600 miles. I had the oil changed per regular maintenance. Shortly thereafter, it was found to have a "leaking shock." Then at a recheck as I questioned it, they found the power steering switch leaking. The work was done by the dealer. Within a day after picking up the car, the blower switch on the dash that regulates the amount of air stopped functioning properly. Sometimes it just blows nothing from the floor, even though the A/C is on and it's supposed to be cooling the car. All of sudden, this is temperamental. What is causing all this?
ANSWER: Don't worry! Your car isn't going to crumble before your eyes. Many times during a service, additional issues are discovered, and not all faults may be noticed without a thorough inspection.
It's not unusual for a shock absorber or strut to leak after traveling 50,000 miles or more; same with a power steering pressure switch. Shock and strut seals withstand countless jounce and rebound cycles, and power steering pressure switches have as much as a thousand pounds of pressure within, trying to escape.
It's difficult to be sure of the cause of your current problem. Is this a blower speed or mode (air delivery destination) complaint? Also, it appears your car may be equipped with either a manual or automatic heating/ventilation/air conditioning system, and this alters the manner in which it's diagnosed. The Ford/Mercury manual HVAC system uses old-school resistors to regulate blower speed and engine vacuum to provide needed movement for mode control doors. Resistors can burn out, but they usually stay broken. A faulty electrical connection or flaky switch could result in intermittent operation. Vacuum controlled mode systems typically divert air to the defroster position when in trouble, to prioritize visibility. A vacuum leak or kinked hose typically remains that way also. Diagnosis of this type of system is fairly easy, requiring mostly mechanical smarts rather than fancy tools. Accessing many of the parts is usually tough due to their location behind the instrument panel.
If your Mercury employs automatic temperature control, a system fault will likely set a diagnostic trouble code, suggesting a greatly narrowed path to resolution. Scan tool data will also indicate if successful blower speed and mode position signals are being requested by the control switches and where various ventilation doors are positioned. I hate to sound like a broken record, but this'll require a dealer or heads-up independent shop job to diagnose and repair.
I can't imagine a connection between any of the Mercury's recent faults. Car problems seem to be like seeing a deer cross the road in front of you - there's always one or two more close behind. Your Grand Marquis has a solid reputation for durability. I'm hoping for smooth sailing after getting past these bumps.