recently replaced the evaporator in my 850. After getting everything back together and preparing to recharge a/c. I found that the entire A/C-Heater unit has no power and that the dash light stay on. Only after disconnecting battery do the lights go out. I have checked and rechecked numerous time over the last two weeks every connection that I unplugged and found nothing amiss, no fuses blown, relays have been replaced with others . I have even gone as far as back feeding 12v into system at the major power wires in and around the blower fan relays and such, nothing. I have checked grounds applied extra grounds, nothing. I have two other 850's, however they are both ACC types while the one I am stumped on is a manual a/c. The only unplugged unused connections is a yellow multi-pin connect attached to a bracket under drivers trim panel. However it has a dummy female plug into it for protection I suppose. Every thing else works fine. Feel free to contact me via this board or e-mail, or I can provide a phone number, thanks

 

Hi Guy, welcome to the forum.

I don't know what the problem is but have you considered replacing the unit? Has the system been serviced?

 

Is your serpentine belt on? No belt = dash lights on.

 

Once again I just replaced evaporator. After putting every thing back in place, hooked up every wire/plug combination I unplugged, replacing orfice tube and dryer, all o-rings etc. I crank engine try to engage a/c so as to charge, but the entire heater/a/c was dead, no power. rechecking every connection multiple times using volt/ohm meter,frequency generator, old school trys of providing power to a/c circuit, still nothing electrical side dead. The odd part is the radio can be turn on and off with out key and dash light stay on until the battery is disconnected. re-connect battery and dash lights stay off. I am former ASE ceritified in imports, factory trained by BMW, Madaza, and Ford., This one has me stumped. When I say dash lights I should clarify it is the dash board illumination lights, not the the idiot lights.

 

If the radio can be turned on with the ignition in the OFF position and it couldn't previously, I would venture you have a bad ignition switch.

Might help with the AC power problem too as power for the heater and AC is controlled by the switch as it cuts power to the AC compressor and blower motor in OFF and Start positions.

 

next chapter in this saga. Have used a good known prefect working order 850 as an parts car. I have swapped every relay, circuit breaker, ign ignition switch etc. I have determined that overload relay #3 is closing when ign. switch is in on/run as it should, but it is not opening when ign switch is of. Therefore keeping radio,windows powered.

I have not been able to find a good enough wiring diagram that can show me what is triggering relay, were does switch side of relay originate?

 

You can find a wiring diagram in this PDF document.

http://www.matthewsvolvosite.com/for...pic.php?t=8018

 

After all was said and done, of all the electrical connections that plugged together that for the most part cannot be cross connected, colored coded, and if there are identical plugs with in path of harness most are some distant apart. Not so for to identical plugs at the blower resistor. Cross plugged you developed afore mention problems in early post.