Testing Relays
 

The Search found me nothing so......

Is there a multi-meter test I can perform to check relays ?
In searching the archives, the only suggestion was to plug a relay into the horn socket to see if the horn blows.

The BB can do better than that, can't it ????

The relay has 5 numbered terminals.

Numbers 85 and 86 are the coil and an ohm meter should show very little resistance if it is not broken.

Number 30 is the relay common. When 85 and 86 are not energized, an ohm meter will show zero ohms between 30 and 87a and "infinity ohms" (open circuit) between 30 and 87.

If you apply a 12vdc source to terminals 85 and 86, you will feel/hear a click and the ohmmeter will read 0 ohms between 30 and 87 and "infinity" ohms between 30 and 87a.

OK?

Here's a few hints: Check coil for resistance or open; be aware that the red relays have a diode in parallel with coil. Check operation of the contacts with resistance or continuity multimeter function while using 12 volts from the battery to energize coil. Jim

Perfecto.

I'm back in business.

Thanks....

Yep, that sounds exactly right, of course it is much easier to plug it in to the horn socket and see if the horn will blow. ;)

The coil resistance is typically in the 70 - 90 Ohm range, and getting an 'open' or infinite resistance at terminals #85 and #86 could explain the problem!

Also, the socket terminals can be corroded, and testing in another socket won't tell you where the problem is!

The wiring and terminal designations are identical, whether the relay is of the round, multipurpose Black, Red, Gray, Tan, or aluminum-case variety, or of the DIN 'icecube' type ... so testing is a useful tool, and familiarity with the electrical system components never hurts!

<b>One final note ... Terminal #85 is ALWAYS GROUND! The RED relays could catch fire or be destroyed if you apply +12 Volts to Terminal # 85 and ground to Terminal #86!!!</b>

Warren,

Thanks for the clarification.

However...if you build a circuit from scratch, or if the original circuit does NOT use a diode....85 and 86 can be reversed, they're bi-directional for black/ non-diode relays.

--Wil Ferch

Not book info but,

I've measured about 300ma-400ma for relay current draw.. and I've heard that relays can become stuck in the contact closed position.

Which relay is the WUR one -- on CIS cars? Is it one of the ones in the back? Which one?

There are two relays on the driver side rear, in the back.
The one on the outside (toward the left rear tire) is the Rear Window defogger Relay and the one on the inside (engine side) is the Heater Blower.

Funny, I'm trying to hunt down the same WUR voltage source.

Stay tuned...I'll find the d@mn thing......

Viola !!!
I think I'm closin' in on it.
80 -83 WUR is energized from the Oxy relay which, on my '80 SC, is under the passenger seat - square silver one.
I tested it per the brilliant minds giving me advise and .... low and behold .....it failed. The coil had 80 ohms but the 30 ---> 87b is bad.

Hello Wayne...my credit card number is ___-______-___.
I think I'll be smart and pick up his book while I'm at it.

This Bud's for you. Thanks for the help !!!!

A 9-volt battery can be handy for a quick 'click' test.
If you happen to have a few relays sitting around... or want to test at a swap meet...or...

I have a question about the engine compartment controller relay, aka blower control unit, aka additional blower relay..this is porsche p/n 911-618-153-00...located in engine compartment next to rear wiper relay...question is on an 87 w/manual heat is there supposed to be voltage on pins 9 & 11 with the key in run and the heater levers down? also what is the function of pin 1 (goes to speedo)...that time of year trying 2 get heater to work..can't get blower on motor to run and it looks like bad blower control unit but @ $150 I'd like to be sure before i spend $$$ thnx

My floor heat levers had a switch connected to them in a dirt/dust pile..

I would confirm a good or bad engine blower.. If good then maybe jump the floor switch with a toggle switch because many times I wanted heat but didn't need the blower operating

What's wrong with testing in the horn relay socket? It's quick, easy, and tells you if the relay is working.

your correct Matt.. I assumed the obvious was done.

BTW do you have the routine style devil's sun burn?

Just on my face;)

Ronnie, I'll send you some pics and and story of my trip when I get home from work.

Most Excellent

Small update, now that I understand the schematic.

The regular round relays switch between the 87 & 87a terminals when the coil is energized (85 & 86) BUT on the Oxy Relay (a silver square one) the 87 & 87b poles energize together and likewise open circuit together with the 30 common ground.