TEST 2: Using A Jumper Wire To Bypass The Blower Resistor
Why bypass the blower resistor assembly? Because this will indirectly test the blower switch. This will help to further diagnose the blower speed issue especially when the blower resistor has tested good (or you replaced it and it did not solve the blower speed problem you're trying to solve).
To bypass the blower resistor assembly, all you'll need is a short jumper wire and to know what terminals (on the blower resistor harness connector) to jumper together.
If everything is OK with the blower switch, on the A/C Heater control panel, the blower motor should run as you bypass each blower speed (in the indicated test steps below).
IMPORTANT: Use a small diameter wire as a jumper wire or you run the risk of damaging the blower motor resistor connector's female metal terminals. If you use a too thick jumper wire, you may permanently open these terminals up and create an intermittent ‘open’ problem.
Alright, these are the test steps:
- 1
Disconnect the blower motor resistor from its harness connector and turn the key to the on position (but no need to start the engine).
NOTE: All of the tests in this section are done on the blower motor resistor's harness connector and not on the resistor itself. The illustrations in the image viewer show the front view of the female metal terminals of the blower resistor connector. - 2
Jumper terminals 2 and 3 together and turn the vent position knob to VENT. This is the circuit that controls blower speed LO (see image above).
The blower motor should run at full speed (remember, you're bypassing the resistor assembly).
NOTE: For the identification of the blower speed knob and vent knob, see the photo of the AC-Heater Control Panel below. - 3
Jumper terminals 1 and 3 together and turn the blower switch to the M1 position (the vent position knob must be in the VENT position). Terminals 1 and 3 complete the circuit that controls blower speed M1 (see image above).
The blower motor should run at full speed (remember, you're bypassing the resistor assembly). - 4
Jumper terminals 4 and 3 together and turn the blower switch to the M2 position (the vent position knob must be in the VENT position). Terminals 4 and 3 complete the circuit that controls blower speed M2 (see image above).
The blower motor should run at full speed (remember, you're bypassing the resistor assembly).
Let's take a look at what your test results mean:
CASE 1: The blower motor DID NOT run when you jumpered the indicated connector terminals in the test step above. This tells you that that specific circuit is bad or that the blower switch is bad.
Although it's beyond the scope of this tutorial, you'll need to do two specific things to find out what's going on. The first is to test the blower switch itself by doing a continuity test of the different blower speeds. The second is to check the continuity of the wiring between the blower switch connector and the blower resistor's connector.
CASE 2: The blower motor ran when all of the indicated terminals were jumpered together. This tells you several important things:
- That the circuits between the resistor connector, the blower motor switch and the blower motor are OK.
- That the blower motor is OK.
No further testing is required of the blower resistor, the blower switch or the blower motor.
Where To Buy The Blower Resistor And Save
The blower resistor and the blower resistor connector aren't expensive parts, especially if you shop for them online.
The following links will help you comparison shop for the original Motorcraft and after-market blower motor resistor and the resistor connector:
Wondering if the above blower motor resistor and connector fit your particular 4.0L Explorer (Ranger, Mercury Mountaineer), don't worry. Once you get to the site, they'll make sure it fits by asking you for the specifics of your particular vehicle. If it doesn't fit, they'll find you the right part(s).
More Ford 4.0L Tutorials
You can find a complete list of 4.0L Ford troubleshooting tutorials here: Ford 4.0L Index Of Articles.
Here's a sample of the tutorials you'll find in the index:
- How To Test The Fuel Pump (Ford 4.0L).
- How To Test Engine Compression (Ford 4.0L).
- How To Troubleshoot A No Start (Ford 4.0L).
- How To Test The Fuel Injectors (Ford 4.0L).
- How To Test The Ford EGR Valve EGR Vacuum Solenoid, DPFE Sensor (at: easyautodiagnostics.com).
- How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L) (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!
