1986 Bronco II A/C clutch field coil - no power

[jbldsdad]

[1986 Bronco II, 2.9 v6]

Great help from this forum over the past few years helping me resurrect this gem from the dead.
Detailed her last week to a beautiful shine.

With the summer still on, I figured I'd take on the (stock) A/C. Replacing hoses, I figured I'd check the compressor before closing the checkbook.
With a direct jump from the batter, car running, the clutch engages and runs!
Otherwise...no A/C from inside the cabin, so I started troubleshooting. (Clearly I'm stuck, or I wouldn't be posting...)Found the 30A fuse blown, so replaced that.

• A/C button pressed (defrost mode), the light illuminates...
• WOT relay (picture attached) seems to fit the "2.3L EFI" diagram from this post. With the WOT relay removed (KOER) I read:
  • 13.63v from the far left red wire (See picture below)
  • .43v from the center red wire
  • 13.73v from the Lg/P wire
  • -.04v from the B/lg wire
• WOT relay installed (KOER) I read:
  • 13.60v from the far left red wire
  • 13.6v from the center red wire
  • 13.65v from the Lg/P wire
  • 13.65v from the B/Lg wire
• 13.6v on the near-side of the pressure switch connector.

So far so good! (A/C button --> WOT relay --> pressure switch: energized!

I add a jumper between pressure switch blades (Just to eliminiate a possible failure there) and the fuse blows.

I removed all tape and plastic casing around the B/lg wiring headed to the compressor for a visual inspection, and I see no visible shorts. I confirmed the ground wire is clean/secure on the passenger wheel well. Just for kicks, I test for voltage on the A/C clutch connector (red lead to the battery "+"), and both blades read 12.38v.

Here's where I'm raising my hand for what to check next.

Other than the fusible link, I wouldn't think there'd be a closed circuit between those two blades, so maybe a short in that connector?
I'm also curious about the BK/Y wire coming off the A/C compressor (one leg goes to the pressure switch, the other seems to head to the EEC), as that white connector looks confusing. (4 red wires, B/Y and a ground wire all meet)

Any recommendations on where the short might be?

 

[RonD]

Don't have a 1986 AC diagram but do have a 1991

Power path should be

AC switch(12v)---------pressure switch------WOT relay-----AC Clutch

Ford liked to use these micro relays seen here: https://www.gtsparkplugs.com/images/micro-automotive-relay-wiring.jpg

But also the mini relays seen here: https://www.gtsparkplugs.com/images/mini-automotive-relay-wiring-840x.jpg

The slot locations are different the the numbering does the same in each

85 and 86 are to activate a relay, one is 12v and the other a ground to activate the relay, remove either and relay is off

30, 87 and 87A are the 30amp contacts that pass power(12v) to the device being controlled

WOT relay is used a little differently than most relays, as its TURNED ON to shut AC compressor OFF
So its normal state is OFF

So WOT relay MUST BE a 5 pin relay or it won't work, make sure you have a 5 pin relay in the WOT base

So slot 30 and 87A are the slots used to pass 12v to the AC clutch inside the relay

At Wide Open Throttle, computer activates relay so connects 30 and 87, so no 12v to AC Clutch and AC is off

Test voltages with key on engine off
With AC switch on, WOT relay pulled out
slot 30 should be 12v or slot 87A, test it
If so then turn off AC switch and retest, no 12v now
This means AC switch and pressure switch are wired up OK

If no 12v on either 30 or 87A then could be pressure switch or AC switch in cab

If 30 or 87A has 12v then when you plug in the 5 pin relay you should hear the AC Clutch "click"
If not then the "other slot", that didn't have 12v is not connected to AC clutch

 

[jbldsdad]

Thanks for the quick response!

I noticed the same feedback to another person, and that comment caught my eye: "WOT relay MUST BE a 5 pin relay or it won't work, make sure you have a 5 pin relay in the WOT base."
The picture I posted shows 4 pins (and a 'stub'?). I only have 4 wires going to the relay. I'm not the first owner, so is it possible that 5th wire is missing/modified?

Meanwhile - I did he test(s) as requested:
Since I don't have two wires at the top (2) blades, I'm not sure if the (lg/p) wire is 30 or 87? In any case, I do get 12v on that wire with the a/c button is pressed and 0v when it's not. So we're good from the a/c button, through the relay and to the pressure switch?

After replacing the WOT relay, no "click". The A/C button is still illuminated, so the fuse hasn't blown again. (I went through 3 today, testing)

So there's something wrong with the wiring between the pressure switch and the A/C clutch...

Does having both the connector wires at the compressor reading 12v provide any hints? (red probe on the battery "+", black probe on either blade - both read 12v, and I get continuity between those blades.)

 

[RonD]

It only needs 4 wires, but the relay needs to be 5-pin model

4 pin relay has no 87A, so no ability to pass 12v to the AC Clutch when relay is off
As said, its a "reverse" relay setup for this, passes 12v when relay is OFF, cuts the 12v when relay is ON, which is why it doesn't need the 5th wire

Look at the diagrams of relay bases, which one do you have, mini or micro?

We/you do not care about slots 85 and 86, they are for control, and there is no control of this relay required UNTIL you are driving at Wide Open Throttle

Just test slots 30 and 87A only 1 will have 12v, key on, AC button on

WOT relay will never "click", unless you were driving at Wide Open Throttle, and I doubt you would hear it, lol

 

[jbldsdad]

Definitely micro.
(bottom 3 are horizontal, top two are vertical)

 

[jbldsdad]

Any tips on troubleshooting power getting to the A/C clutch connector?
I'm seeing voltage in both blades of that connector. Seems like a grounded wire?

I'm guessing the 'dashed' lines are energized and the 'solid' lines are grounded. That would suggest the blades on the a/c compressor expect a positive on one side and ground on the other. (Yet I'm finding both sides will read 12v with the other probe on the battery "+".

The diode...(fusible link)...looks like it joins positive and grounded wires which isn't making sense to me. Thus, I'm unclear on how to troubleshoot "no power" getting from the pressure switch to the a/c clutch switch. What am I missing here?

 

[RonD]

If the AC Clutch is plugged in then BOTH wires should show 12v if AC is on
Clutch is just a coil of wire, so 12v in = 12v out
If you unplug the AC Clutch connector then one wire will be 12v and the other 0v, a Ground

If both wires show 12v when its unplugged then the Diode is bad

12v-----|<------0v

12v---->|------12v

The line on a diode blocks "+" voltage

The diode is there to prevent voltage spikes as the clutch engages and disengages so frequently when in use

 

[jbldsdad]

Very helpful. Thanks!

Now...I'm not finding many leads on where to find a replacement diode. (I would have assumed an in-line fuse, but a quick search proves that's a mistake)

The only clue I've found so far is to grab one off a donor vehicle. I've been semi-restoring this truck for a few years now, trying to do it right. Is there a better option for a diode replacement? New?

 

[RonD]

You don't need the diode hooked up to test the system, so remove it so the 2 wires are no longer connected together to continue testing the system

Yes, wrecking yards would be best bet, but you can get diodes with wires attached to splice in for $25-$45

 

[jbldsdad]

Thanks for the tips!

So I cut out the diode and retested...still getting a 'ground' on both blades of the compressor connector. Tracing the B/Y wire toward the EEC, it appears to connect directly to a ground wire. (Black wire in this picture is grounded to the front body.) Not being the original owner...is that wiring correct? (A/C has never worked since I bought it)

 

[RonD]

The 12v wire(black/yellow) on the AC clutch should go to the WOT relay, on passenger side inner fender

There are 3 relays used if you have AC
Brown Base relay is the EEC relay
Green Base relay is the Fuel pump relay
Black base is the WOT(wide open throttle) relay

WOT relay must be a 5 post relay, as it passes 12v power to AC clutch, when AC is on, all the time UNLESS driver presses gas pedal to the floor, at WOT the EEC activates this relay to turn off AC for best engine power

The 12v comes from the switch in the cab, passes thru the pressure switch and then to the WOT relay, then out on the black/yellow wire to AC Clutch

12v IN from pressure switch at WOT relay should be dark green/orange
This wire also connects to EEC as a Monitor wire, so EEC knows AC is on so it will activate WOT relay as needed

This is from 1991 AC wiring so not sure about 1986
But AC is pretty straight forward in its wiring and how it works
AC is either on or off, no temp control

Switch in the cab, when on, sends out 12volts to the AC clutch
This 12v usually passes thru 1 or 2 pressure switches and then to a WOT relay, which always passes the 12v directly when off, 5 post relay
And the 12v goes to the AC Clutch

Cab switch(12v)-------pressure switch------WOT relay----AC Clutch--ground

Not a lot to it, the pressure switch cycles AC Clutch off and on based on pressure, so compressor doesn't burn out if pressure drops to low or hoses don't blow off if pressure gets too high

 

[jbldsdad]

Great summary, but that isn't addressing the grounded ac clutch (b/y) wire.

I see we keep referencing a 1991 wiring diagram which does not reflect this '86 B2. I'm attaching an accurate drawing (albeit Microsoft Word 'chicken scratch') showing the actual path as:

Cab switch -->WOT --> Press switch --> A/C Clutch --> Ground

It's the plug intersecting [4 red wires, (b/y) and a (p/y) + (b) wire] that has my attention now. For some reason when I test between battery (+) and the (b/y) wire at the A/C clutch switch, I'm getting 12v. Given one branch of the (b/y) wire goes to that plug which has a body-grounded (b) wire - it makes sense that it's grounded (but shouldn't be?) However, even when I remove that front-facing ground wire from the body, the (b/y) wire at the A/C clutch is still grounded.

Anyone have a wiring diagram for this '86 Bronco 2 showing where those wires should go, and for what purpose?

 

[RonD]

Found this thread here: https://www.therangerstation.com/fo...king-for-a-ac-diagram-for-1986-ranger.194161/

"AC De-ice switch" is the pressure switch

Not seeing the extra wiring you are

Not sure how you are testing for a Ground
0 ohms to battery negative is a ground, 2 ohms and up is a relay or AC coil's ground, not a direct ground

 

[jbldsdad]

I found the '86 digrams in the back of a Haynes manual. The reference above is for an '87, and it appears the routing is a little different (a/c clutch --> WOT --> pressure switch in the '87, but ac clutch --> pressure switch --> WOT in the '86. (As I'm visually confirming in my truck)

Diag1 shows the routing (347) from the a/c compressor --> press switch --> WOT... Also the two red wires (331 & 361) and a lg/p wire (348) coming from the WOT...

Diag2 shows (361), (331) and (347) terminating in a connector (1448) connecting off-page to 12A581.

Diag3 appears to be the other end of that connector (14A459), where the same (331), (361) and (347) continue on to the EEC (not shown, but validated). The diagram shows an lg/p (348) leaving 14A459, but not entering (14489). In my previous post, a picture of that connector under my hood just doesn't match up. There's no lg/p (rather an empty socket), and the (b/y - 347) is jumped into that blue connector where a purple/yellow wire heads toward the EEC, and (b) wire heading elsewhere. (Assuming it was to be grounded, I grounded it next to the radiator) Unless I'm looking at the wrong connector in Diag3...

Anyone with more of an electrical background than I (none) recognize this? (I can scan/upload the full page diagrams if it would help)

 

[sgtsandman]

With Haynes and Chilton manuals, always trust but verify. They get you by but they have been known to have bad information as well.