Relay question

[ftpiercecracker1]

Is this a "change over" relay? If so why and how does it function?

 

If not why does it have 5 wires?

 

 

 

 

It was my understanding that a five wire relay is used so that when the relay is energized a particular device is powered and when the relay is denergized another device is powered.

[gogmorgo]

It does look to me as though that's what it is. The function can be achieved with a standard automotive relay, which switches power (supplied to pin 30) between 87 (normally open) and 87a (normally closed). 

As to why it's set up like that, tough to say, because it seems to be alternating between supplying power and ground to the a/c relay and rad fan. The ground could be something to do with the diagnostic connector, possibly to disperse induced voltages from either the a/c clutch or rad fan (solenoids, motors, collapsing magnetic fields and whatnot), or it could be a sneaky and unorthodox way to prevent the rad fan's temperature switch from also triggering the a/c clutch (unlikely but AMC could be creative sometimes). Changeover relays can also be used for latching, but I don't think that's what's going on here. 

[Minuit]

You can use five-wire relays any way you like, it's just that switching 12V between two devices is a fairly common use of them. In this case, the normally closed (i.e. the relay coil is not "on") contact of the relay serves to ground both sides of the compressor clutch and diode. I assume this is to shunt any flyback voltage to ground and protect the diode (which is also there as flyback protection). When coils and other inductive loads close, there can be quite high voltage surges that can cause damage to electronics. That's also why you'll often see diodes across the coil of relays. Same idea.

 

When the relay is active, the clutch receives 12V and engages, turning the compressor.

[Ωhm]

When this relay is picked, power from Pin_4 is routed to Pin_1 and the AC clutch/Rad Fan is activated. When AC clutch/Rad Fan is deactivated, the winding of the wires within the coil/motor can cause a large voltage spike unto the circuit. Note Pin_1 is routed to Pin_3 and to ground. This configuration will tie both ends of the AC clutch/Rad Fan to ground. I believe this is added protection for the clutch diode.

[ftpiercecracker1]

So it just grounds out any residual back current and shouldn't mess with its configuration. 

 

 

 

Here's another question related to relays.

 

The starter relay, why is it needed? My starter, as most starters I've seen have a piggy back solenoid directly attached which does the job of the "starter relay" pic attached.

 

 

 

 

 

 

The only time the relay is energized is when you are trying to start the engine, meaning it is denergized in all other positions, other wise the starter would be spinning with the key in any position except for off. Having a second relay that sends power to specifically trigger the starter solenoid, which is what actually connects the starter directly to B+, seems redundant. Why not have the ignition wire that is energized with the key in start position run directly to the starter solenoid?

[ftpiercecracker1]

More baffling electrical.

 

Link to diagram

http://jeep.zerok.ru/index.php?page=196

 

 

The yellow wire is energized when the key is turned to run. This wire triggers the fuel pump relay but also supplies power to the O2 heater relay. 

The O2 heater relay is wired such that when the relay is energized power is cut to the O2 heater.

 

From what I am seeing both the yellow wire and the trigger wire for the O2 relay are energized simultaneously. Meaning the O2 is never heated.

 

The only thing I can think of is the ground wire for the O2 relay, which does go directly to the ECU, must be timed/controlled by the ECU. Did I just solve my own question? 

 

[Ωhm]

57 minutes ago, ftpiercecracker1 said:

shouldn't mess with its configuration.

1. Starter Relay bypasses Fuel Pump Ballast Resistor during CRANK.
2. Allows for P/N function if equipped with Automatic Transmission. Not your problem.
3. Provides stud for Battery/Fusible Links.

[gogmorgo]

It also takes a fair bit of current to fire the starter solenoid, as it does have a pretty hefty gear to be shifting, and it needs solid pull to get it engaged. The added relay means you're not running all that current through the ignition switch, NSS (if equipped), etc. 

The more I've looked at the diagrams on that Zurok.ru site, the less confident I am in them. They may be correct, but they're not always labelled correctly. There's a decent electrical manual on here somewhere, check the DIY master index maybe. 

[ftpiercecracker1]

14 hours ago, gogmorgo said:

It also takes a fair bit of current to fire the starter solenoid, as it does have a pretty hefty gear to be shifting, and it needs solid pull to get it engaged. The added relay means you're not running all that current through the ignition switch, NSS (if equipped), etc. 

The more I've looked at the diagrams on that Zurok.ru site, the less confident I am in them. They may be correct, but they're not always labelled correctly. There's a decent electrical manual on here somewhere, check the DIY master index maybe. 

 

 

Thanks for the tip. 

 

I have both my engine bay harness and cab harness totally gutted and splayed open. I'm removing all unnecessary circuits and fixing lame factory connections. Thus far every single wire/plug/connection I've traced has been accurate, as far as color and location, but it does lack some wire paths that just leave you guessing.