FJ40/45 AC Question

[wngrog]

Hey guys.

I have a 1982 FJ45 with factory AC.

When I got the truck it had a hacked up harness with a toggle switch making compressor kick on.

I redid all the wires. Bought a new controller. Got all of the wires back to stock but the signal wire won’t engage the compressor clutch.

If I add direct 12v the compressor kicks on. It’s just not getting a signal.

It was suggested the relay is bad but I can’t find the damn thing.

 

[JaxFJ]

1. Wiring Diagram Overview:
   • The AC relay (item 7) in your wiring diagram is responsible for controlling the signal to engage the compressor clutch.
   • It appears the AC relay receives power from the heater fuse (item 8) and is triggered by inputs from the control switch and possibly the thermistor or oil pressure switch.
2. Relay Location:
   • The AC relay is likely mounted near the heater fuse box or along the firewall under the dash. It’s often a small gray or black box (like the one shown in the relay photo).
3. Relay Part Details:
   • The relay part number in your photo, 90987-02028, is a 12V relay commonly used in Toyota vehicles.
   • If the relay is faulty, replacing it with an identical relay should restore functionality.

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Next Steps:​

1. Locate the AC Relay:
   • Use the diagram to trace the relay’s location near the heater fuse or under the dash.
   • Remove and test the relay with a multimeter to check for continuity and proper operation. If it's not functioning, replace it with the relay shown in your image.
2. Check the Heater Fuse:
   • Ensure the heater fuse is not blown and is providing power to the relay.
3. Bypass the Relay for Testing:
   • Temporarily bypass the relay by directly connecting the signal wire to the compressor clutch. If the compressor engages, the relay is likely the issue.
4. Verify the Signal Path:
   • Check for 12V at the relay when the AC is turned on.
   • If no signal is reaching the relay, the problem could be with the control switch, thermistor, or wiring

1. Locate the AC Relay​

• Use the wiring diagram you provided:
  • The AC relay (item 7) is likely near the heater fuse (item 8) or mounted on the firewall under the dash.
  • Look for a relay that matches the photo you provided (90987-02028).

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2. Test the AC Relay​

Tools Needed:

• Multimeter.
• A 12V power source (battery or bench power supply).

Steps:

1. Remove the Relay:
   • Disconnect the relay from its socket to test it independently.
2. Identify Pins:
   • The relay typically has four or five pins. Using the wiring diagram:
     • Locate the coil terminals (trigger side).
     • Identify the switch terminals (load side).
3. Test the Coil:
   • Set your multimeter to Ohms (Ω).
   • Measure resistance across the coil terminals. It should read around 50–120 ohms.
     • No reading (open circuit): The coil is damaged, replace the relay.
4. Test the Switching Function:
   • Apply 12V to the coil terminals (you should hear a click as the relay switches).
   • Use your multimeter to test for continuity across the switch terminals.
     • No continuity or no click: The relay is faulty.

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3. Check the Heater Fuse​

• The heater fuse (item 8) provides power to the AC relay.
• Locate the fuse in the fuse box (usually under the dash or near the engine bay firewall).
• Test the fuse:
  • Remove it and check for continuity with a multimeter.
  • Replace the fuse if it's blown.

---

4. Bypass the Relay for Testing​

• Temporarily bypass the relay to ensure the rest of the system works.

1. Disconnect the relay and identify the signal wire and compressor wire in the socket.
2. Use a jumper wire to connect the signal wire directly to the compressor wire.
   • If the compressor engages, the relay is likely the issue.

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5. Test the Signal Path​

• If the relay tests good, troubleshoot the signal path.

Tools Needed:

• Multimeter.

Steps:

1. Check for Signal Voltage:
   • With the AC turned on and the relay in place, measure the voltage at the relay’s coil input terminals.
   • You should see 12V. If not:
     • Check the control switch (item 4): Ensure it sends a signal when turned on.
     • Inspect the thermistor (item 1): Verify it’s operational and not blocking the signal.
     • Check the oil pressure switch (item 9): Confirm it completes the signal circuit when the engine is running.
2. Inspect Ground Connections:
   • Ensure all components, including the compressor and relay, have proper grounds.
   • A poor ground can prevent the system from working.

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6. Verify Compressor Operation​

• Since your compressor engages with direct 12V, the compressor clutch is functional.
• Once the signal issue is resolved (relay, fuse, or control path), the system should work properly.

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Common Points of Failure:​

• Faulty Relay: Replace if it doesn’t click or pass current.
• Blown Heater Fuse: Replace if damaged.
• Control Switch Issues: If no signal is reaching the relay, the switch may be faulty.
• Thermistor or Pressure Switch: These can block the signal if they detect incorrect conditions (temperature, pressure, etc.).

 

[Skreddy]

@JaxFJ has a much better path to follow. My simple question: what rpm are you; idle? The compressor typically won’t kick on until over 1000 ish rpm. If you’re testing higher than 1000-1200 rpm, disregard everything I said and see above.

 

[fjc-man]

Adding to what Skreddy said, you can ajust the RPM cut-in point in small increments on the side of the controller. With the compressor engaged at idle you would want a speed more like 750-800 anyway. Turn it “on” and try small ajustments and see if you get it to kick on. Hey, if you’re working on a 2F that diagram is for a diesel. You need the speed signal from the ignition coil to the controller. The diagram I posted doesn’t show the pin numbers, I’ll try and look them up.

 

[wngrog]

Mine is a 2F.

Thanks for the FSM info.

I need to find that relay.

 

[wngrog]

I can’t find this damn relay.

 

[charliemeyer007]

Back in the day a lot of parts were NLA so folks hacked the system and just wired in a switch to activate the electric clutch. My deceased BOL wired in a switch on his Blaser to cut the power to the AC clutch when he was pulling grades in the AZ heat, rather than shutting the system off.

 

[Engineer8000]

Pictures I've seen have the relay mounted to the rear top of the evap housing. Also, someone was selling 24V controllers on ebay as 12V units.

fake 12V controller - they are erasing the 24V on the bottom of the controller.

 

[Engineer8000]

The 24V units can easily be modified to work on 12V but they do not have the RPM sensing circuit.

 

[wngrog]

I see where it is looking at old pics. Now I am going to try to get it out of there without pulling the unit and losing my charge

 

[fjc-man]

The hoses going through the firewall have enough flexibility that you could dismount the unit, lower it, and set it on something like a foot tall to get at that relay.

 

[Engineer8000]

Those Toyota relays are bullet proof, I would be surprised if you found it bad.

 

[wngrog]

Those Toyota relays are bullet proof, I would be surprised if you found it bad.

Man. That’s my best hope at this point.

 

[fjc-man]

Nolen, is the low pressure switch on the low side hose near the battery tray plugged in? Has continuity across the pins?

 

[wngrog]

Nolen, is the low pressure switch on the low side hose near the battery tray plugged in? Has continuity across the pins?

It does have continuity yes. It was jacked up but I got it back in place.

 

[wngrog]

Well the relay is clicking.

You know, a 60 series AC has to have a RPM signal to kick on.

This truck now has a Holley Sniper with a tach but there was no tach before.

Am I missing some other signal here?

 

[Engineer8000]

The relay inside the black box controller is what provides power to the compressor clutch. Are you sure your new controller is working? I have seen a few things go wrong in these. I repair and test these.

 

[fjc-man]

The speed signal to the controller comes from the ignition coil, with the stock setup.

 

[wngrog]

The relay inside the black box controller is what provides power to the compressor clutch. Are you sure your new controller is working? I have seen a few things go wrong in these. I repair and test these.

No idea. It was new old stock from my guy in Yemen.

 

[Engineer8000]

Are you sure it is a 12V unit? Do you have the old controller still?