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9.1.3 - Air con Blower testing ( Vladam Temer,  )



The XJ40 has two blower fans in the dashboard. The blowers share some of the ducts. Unless you are quite familiar with the system, it may not become obvious when one of the blowers fails, as you will still have some air coming out on both sides of the dashboard.

The most typical blower failure is a loss of low and medium fan speeds. To test if one of the blowers is defective, follow this procedure:

1. Turn the ignition off.

2. Open the left side fuse box cover and remove the "Aircon" fuse. On the '94 MY car, this is a 20A fuse in position B4. Be very gentle with the fuse box. All the interior contacts are held in place by solder. Every time you pull out a fuse (or put it back in), you are applying force to a solder joint. Solder is not a strong alloy, so it's easy to get a cracked solder joint.

3. Start the engine. Since you removed the left side fuse, the following steps will test the right side blower.

4. Turn the blower control to "low", and listen for fan noise or feel for air out of the vents. Repeat for the medium fan speed; If "low" doesn't work, it's almost certain that medium won't work either.

5. Turn the blower control to "high". If the fan works, the most likely problem is the power transistor in the fan speed control circuit. This part is located in the blower assembly. You will have to take out the blower to do the repair.

If the fan doesn't work on "high" (as well as low and medium), check the two relays in the blower, and the fuse box. In theory, the relays can be replaced without blower removal. In practice, it may be difficult to do that unless you are quite familiar with the blower construction.

6. If none of the blower speeds work, test the 12V supply to the blower as follows:

Turn off the ignition. (Before proceeding, make sure that the right side fuse is good.) The easiest way to test the 12V supply to the blower is to get a test light with a needle in one of the leads. You can also test with any voltmeter and a needle which you will use to pierce the insulation on a wire. Locate the wires coming out of the blower. You will see two connectors. One is rectangular and white, the other is cylindrical and brown.

The cylindrical brown connector supplies 12V to the blower at all times - even when the ignition key is out of the lock. This connector has a black wire and a brown/blue wire on each end. Attach one lead of the test light to a known ground point on the car. Use the needle lead to pierce the insulation on the brown/blue wire and note if the bulb lights up. Be careful not to short out the brown wire to ground while piercing the insulation. If you do, you will be very sorry afterwards and your spouse will lose all respect for you. Remember that the brown wire always has 12V on it, even with the key out of the ignition lock.

On my car, the brown/blue wire changes color after the cylindrical connector and becomes brown without the blue stripe. It's best to pierce the wire on the blower side of the cylindrical connector. That way you are testing the connector as well. If the bulb lights up, the fuse box is probably fine. You can repeat the test with the ignition "on" and the blower on high speed. The light should still glow brightly. If you are using a voltmeter, you should do the test with the ignition "on" and the fan speed set to "high".

If the light doesn't glow, the fuse box is suspect. There is also a theoretical (but very unlikely) possibility that the black wire on the cylindrical connector got detached from chassis ground. You can test for that by getting a second needle and piercing the black wire near the blower. The light should now be connected between the brown/blue and the black wires, and it should glow.

7. If the right side blower works, repeat all of the above for the left side blower. Don't forget to put the fuse back in.


 

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