Chrysler Repair: 87 Chrysler 5th avenue/intermittent air, amp fuse, rear wheel drive

Question
Goodmorning Roland,
I have a 1987 Chrysler 5th Avenue with very low miles which I love but the air (air conditioning/heater) is intermittent at best.  Sometimes when I go over a bump the heater starts working but then cuts out when I go over another bump.  Once it starts working the heater blows hot and ac blows cold.  The only thing is that I never know when it will work.  I've tried playing with the temperature slider (back and forth), turning it on and off.  You mentioned vacuum in earlier posts? Not sure how that would affect intermittent blower problems. I'M FREEZING...PLEASE HELP!  Thank you, Raymond

Answer
Hi Raymond,
My '87 front wheel drive manual lists the New Yorker, but not the 5th Avenue. Is your car a rear wheel drive model? I do have the '83 shop manual for the rear wheel drive but again no 5th Avenue there. In any case, if the wiring is similar there should be a fuse socket that sends 12v to one side of the blower motor when the ignition switch is in the 'run' position, then the other side of the motor has a wire that goes to blower speed switch thru one of several resistors in what is called the 'resistor block' and then after passing thru the speed switch that wire is grounded. You could be loosing the blower because of a loose fuse or a fuse that has a crack in the conductor which is opening and closing spontaneously, or there could be a loose connection in the control switch, or the resistor block could be breaking down electrically. If the block were going bad the result would be that the blower would only run at the high speed setting, otherwise it probably is not the problem save for a loose wire at its connector. So I would look closely at the 30 amp fuse (shown as #4 in '87 New Yorker) that powers the fan and see if it is loose, has a crack, or has a corroded contact. Then see if the fan switch might be bad by checking whether it operates as flakey in all the different speed settings. Finally, get under the dash and find the blower and nearby check the plug-in for its wires to be sure it is isn't loose in its socket. I can tell you about the resistor block and how to find it if you strike out after trying these first.
I hope you can get the fan going, but in the meantime be thankful for global warming :)
Roland