Central Locking stopped working
 

I have an 84 Volvo 240 and the central locking system crapped out on me. Checked all the fuses and electrical and all seems fine. So I start taking off the door panel and got everything off but the window crank. I got the screw out of the center but it will not come off. Is there a certain trick to this? Also I need to know what to look for when it comes to the central locking troubleshooting.

according to the wiring diagram, 84 240 central locking has two relays, 'lock' and 'unlock'.

here...

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I do believe I'd start with my digital multimeter at those relay sockets (relays unplugged!), and verify all the right signals are getting to the right places. the pin 86-87 on both relays green wires should be always-hot, whether ignition is on or off. if there's no power there, check fuse 8, and the green wire coming off the fuse spade middle or left column on the fuse 8 row.

if you use a jumper wire to briefly connect pin 87 to 30 on the 'lock' relay, the doors should lock. if you do the same on the 'unlock' relay, the doors should unlock. if that all works, then the lock solenoids are fine.

if the doors lock and unlock, then connect a ohm meter between pin 85 of the 'lock' relay socket and ground, and depress the drivers lock, you should see conection (0 ohms), release the lock and it should go open circuit (infinite ohms, sometimes 0L overload on a digital meter). connect ohm meter to to pin 85 of the 'unlock' relay socket, and lift the lock, and you should see 0 ohms connectivity, release it and 0L/overload/infinite ohms.

if someone inserts the key and turns it to lock, and to unlock, you should see the same 0 ohms on pin 85-ground of the appropriate relay.

if those ohm tests fail, then the microswitches in the door locks are the problem. if they pass, then its maybe the relays.

oops, my lock/unlock test of the solenoids won't work as written above.

with both relays unplugged, you would have to jumper one relay pin 30 to 87a (ground) and the other relay pin 30 to 87 in order to lock or unlock the door locks.

my ohm test of the plunger and key switch are, I think, still correct as written.

all this was developed under the influence of a few pints.