hi , sometimes ( often…) due to high heat, the contact mounting pocket of switch back melts from the current , then contact is unstable recedes into rear plastic.
Really , there is too much current on AC cars for a thermoplastic switch to handle , then the high speed contact does not mate with the slider inside .
Related , any wiggling of those wires on the protruding part of switch( (that is the hi fan and ac contact , —the larger different switch “end look “ than a non ac —obviously) WILL loosen the flag on the rivet going through plastic in to the contact , main reason it heats up . Almost 30 A flows . I know this issue from Dodge 70’s truck heater fan on hi , both the speed switch burns up and the 30 A fuse holder end melts in the fuse block . Same reason . Darts too They needed better EE’s than they had ( the same guys that brought you melting bulkhead connectors, running 40 A through 1/4 flags , —- they are 15 -18 A things ) .
Due to this flaw and fragility, Correct removal of wires on the high current AC switch end means turning small screwdriver between black hood of female wire and metal of male tab ,(not the plastic) Any wiggling and pulling will cause this loose rivet failure . Did not happen much on older cars with same design switch as switch backs were phenolic , they did not melt .
Back to 300 switch , early on (F) I tried to solder the flag to the rivet , but that makes it sink in even worse , ( solder temp melts the housing quickly) later used a setup with a “third hand “to try to keep it about right , then soldered it ,(while disassembled ) but contact was still no good inside as it had moved back , or tilted . Leads to frustration unreliable repair messing with it by hand
As they are hard to find , (variations of AC switch ) in early days , had to fix it — so then we set up tooling in machine shop to machine the inner pocket and contact plane about .030 deeper ( only as needed ,absolute minimum ) this evens plastic and contact again ,into same plane , fixes it back to stock — but loose rivet (now soldered ) will not matter or heat up from that cause . Contact might … YMMV on repair — some are melted too bad to fix . have to be spotless shiny so solder “ takes” fast or you wreck it .
Wrecked a few early on ..
For example You cannot tighten rivet with hammer and block it fails again ( plastic sandwich is a loser) cracks too .
We can fix most as described ,gets you new button cams too ,so - “ wow” the buttons work right , can fix bad nipples too .
DO NOT wiggle that vacuum plug either or you break off the nipples . Mechanics do that all the time , destroying switch . Forewarned is forearmed . Pry it straight back two screwdrivers . Lock clips not needed on that .
Generally 3-4 nipples worth fixing — more it might he better to find a new junkyard core switch . We have replaced all of them , if all broken , up to you
See Forward look parts website for detail, more nipples are more $ . each one takes 20 min. with tooling . No tooling they always come out crooked / angled .
Correct solution to all this is to add a 30 or 40 A 12 dc fan relay driven by the contact … like real cars have . If enough demand , might make a kit/ harness , or you can figure out , if so inclined . Let us know any comments on a kit / harness for relay
Long story , but what happens..
John Grady PE
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