Tired of it thinking it’s satisfied when it’s still 80plus degrees in car! When it works it works fine, but then your hear the relays slow the fans down then off, then nothing works, even moving switch to defrost only puts fans on low, high and low do absolutely nothing when this happens, every time i try to test it, everything works fine!!!! Inhave followed numerous threads here, saved them, and no form of testing gives me any ideas!! Will
my ac stay cold if I just add a switch to the fan wires and throw a full 12 volts at them? Or will some servo somewhere start adding hot air?? At my wits end!!!!

 

I had an 83 XJS that had the exact same problem, It would be 95+ degrees (LA) and all off a sudden the heater would come on full blast!!! Never figured it out but there is a couple of You Tube videos explaining how the system works (or not), and how to convert it to manual operation. It may be a bad amplifier, inside temp sender or a leaky air duct shooting cold air on said sensor making it think that its too cold, hence turning on the heat. Not kool!!! (pun intended)

 

There is more to it than just changing fan speeds. The servo, controlled by the ac amp, operates flaps to blend hot and cold air to reach the desired temperature. If set to heating mode, you won’t get any cooling!

There are some tests you can perform to check various sensors etc.



I have developed a replacement AC amp, so if you determine your amp is not working (very common after 40+ years of use), you could PM me for more info.

However, if the fan speeds do not alter with different positions of the mode switch, then you have a further problem, possibly with the micro-switches on the mode switch or with the fan relay.

 

Will try again with testing, hopefully it stops working this time and I can do the tests
thank you

 

Thought maybe I had found the issue one of the micro switches was not making a good contact, couldn’t get continuity through it, just a bunch of resistance, swapped it out ( as I had a set of them from testing before ) now it has good continuity when switched, but no change in operation!!! As yes it’s currently not working, but theres a possibility I put a wire back in wrong spot, anyone got a
picture of the wiring connected to the mode switch? Or at least can tell me which switch is which, schematic just has switches a,b,c,and d pretty sure I got it right but would to verify oh and I also found the pin on the vacuum switch there bent and not allowing it to slide , so replaced it too!!

 

I'll post what I have, Darren, one or two might help.





(';')

 

Thank you Elinor!!!
looks like I have the switches wired correctly based on your pink wire and the black and white!!! Guess I’m still digging!!! But wouldn’t you know it, it’s working again right now!!! So frustrating!!!

 

Oh Goodie! An Intermittent!
What Fun!
not
(';')