2005 Mercury Marquis - A/c still intermittently blowing after blower replacement

run this test to see if the EATC Control head for you ac and heating is bad turn car off, close doors, start car w/EATC off, hold both off and floor buttons simultaneously, release both buttons and press automatic button w/in 2 secs. self test will begin, takes about 2 mins. If all lights come on, unit is probably good. If a code appears, need to check if unit is bad. If unit is good, Code of 888 is a pass any other code is a fail.

The KEY clue for me is the sensitivity to vibration. In my 45 years of electronic servicing I have found an appalling use of brass rivets as conductors on double clad copper PC Boards, typically it takes about 5 years for humidity and electrolysis to create corrosion and about 2K ohm resistance between these two dissimilar metals, in dynamic trouble shooting the technician would find an 12V voltage drop between the two sides of the speed control power transistor PCB, in static troubleshooting you would use a VOM to locate the 12Volt drop, however I always just clean all of the rivet connection on the PCB with a wire brush and carbon tetricloride and solder each rivet on both sides of the PCB... The Power transistor PCB is mounted on an aluminum heat sink an tucked away inside the AC flume located on the fire wall below the windshield of the engine compartment, you will need a 3/8 socket to remove the two bolts it to the flume. In my 45 years as an AVIONICS technician on aircraft I have never found this insulting practice used in fixed or rotary wing aircraft but only in land mobile vehicles and marine craft. Good Luck you youngins, n 73s to ya. Charlie AT1 USS KITTYHAWK CV63 / W8EIV / FCCP1 / FAA Cert.

I had the same problem on my 2004 Grand Marquis. The blower would stop dead then a bump would bring it back to life. Taking the blower out, it works fine. I discovered that the resistor module was the problem. With ETAC the resistor module is a power transistor that the ETAC throttles current to the blower. The little circuit board that the power transistor sits on is poorly designed. One of the circuit traces intermittently goes open circuit and it stops working. A little scraping and solder fixes the problem permanently. I don't know if a new resistor module has a better designed circuit board. The poor circuit board design is a time bomb waiting to go off.