Resolved Checking Relays?

[805eclipse]

I was wondering how to check if the relays in my car are good or bad?? my door locks, radio, and interior lights just went out so i want to check them. Thanks

 

[Amazin' Wasian]

we were just talkin about this in my shop class the other day, and my shop teacher pretty much said its a pain in the ass, he said somethin like u have to hook them up with little jumper cable things to your battery and use a test light or a d.m.o.v., if im wrong im sorry i dont know a whole lot about relays. he said the DMOV is alot easier, but im guessin u probably dont have 1. there like 60 bucks. and is like a test light but alot better.

 

[psychlow]

If it's a SPDT relay, for example, you'll have something like below:

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For this relay, you have a N/C (normally closed) post, a N/O (normally open) post, a common post and two coil posts. You'll need a multimeter with a resistance (ohms) option and/or a continuity option.

You would first test the N/C (normally closed) pole's continuity by checking resistance between the N/C pole (87a) and the common pole (30). There should be little to no resistance between these poles. Then, you'd check the resistance between the common pole (30) and the N/O pole (87). There should be no continuity (infinite resistance).

Next, you would apply 12V between the coil poles (85 and 86). Then, you would recheck resistance between 87a and 30 - there should be infinite (or very high) resistance (no continuity). Then, you would check resistance between the N/O pole (87) and common pole (30) - there should now be continuity (low resistance).

Basically, it's all about understand how the relay works: you apply a voltage to the coil, the coil energizes and closes a switch. A closed circuit should have continuity - an open circuit should not.

 

[Defiant]

we were just talkin about this in my shop class the other day, and my shop teacher pretty much said its a pain in the ass, he said somethin like u have to hook them up with little jumper cable things to your battery and use a test light or a d.m.o.v., if im wrong im sorry i dont know a whole lot about relays. he said the DMOV is alot easier, but im guessin u probably dont have 1. there like 60 bucks. and is like a test light but alot better.

Your shop teacher had better stick to teaching.

Grab a known good one and substitute it into the suspect circuit. If it fixes the circuit, the relay was bad. Or, vice-versa, put the suspected relay into a known-good circuit. If the circuit no longer works, the relay's toasted.

Shop teachers.