Hi all,
As I put the key into accessory position, it seems like the blower works for like a second? Is that possible? the switch does nothing though otherwise and I'm really not sure where to start here.

 

Need more details but on the mark lll system that is normal if the fans are switched on but water temp sensor is not yet switched. If left in that position fans will start up once minimum operating water temp is reached.

 

Welcome Gregory, you need to add the year of your XJS to your signature as there are many differences between the model years over the production run of the XJS.

The AC system was changed a few times and the operation is different. So it's difficult to provide model specific advice without knowing the year of manufacture.

 

I set my signature..thanks for the tip! So the car has to be warm for the fan to come on? It seems like it is fully warm, maybe a bad temp sensor?

 

Does not need to be fully warmed up and may well be another cause. The sensor is easily bypassed with no real downside. It is located on LH side of a/c assembly fixed to heater core water pipe, two wires just need joining together.

 

You have no fan with any settings except from it maybe runs for one second when key reaches acc position ??

The fan should run in defrost setting, even if the control unit senses cold water.

 

This is correct..so what else do I check? Is there a relay somewhere? I'm pretty sure I 've checked all the fuses at this point and all seems ok

 

There is a fuse for each blower Fuse 10 in main fuse panel under the dash and fuse 5 in aux fuse panel under the glove compartment, both of these are 25amp.

Next the orange wire from both blowers goes to pin 16 on the HVAC ECM, this is what controls full fan speed. Disconnect the connector (it is important you disconnect the connector) from the HVAC ECM and put your ohm meter from the Orange wire pin 16 to ground, you should have somewhere around 8-12 ohms.

Report back what ohm reading you get.

 

So I replaced a 3 amp inline fuse on the passenger footwell side and I now have the blowers running all the time it seems. This is when the car is started with the switch in defrost mode. AC is charged and blowing cold. I have yet to run this test.

Another item, it seems if I take that 3 amp fuse out with the car on and put it back in, sometimes the fans seem to kick into a higher blower speed. Is this the switch, or those resistors on the blowers?

 

When you select defrost the system defaults to max heat and high blower speed. So if you start the car with the control in defrost mode it would be normal for the blowers to kick right in, immediately

If your mode switch is in lo, hi, or auto and the temp selector is set for heating, the blowers won't operate until the coolant was warm enough to actually provide heat....as mentioned earlier, I think


Which test is that?


Are you sure this is a problem ?

If system power is interrupted then restored it might take a couple seconds for the system to re-stabilize. Or, it some time has passed and ambient conditions have changed, the system will take a few moments to recognize the change in conditions and adjust itself

Cheers
DD

 

You need to go through the diagnostic procedure, I have attached this for you, you'll see it at the bottom of this post.

Make sure you start at the beginning and work through each test sequentially.


Get you self a couple of these jumper wires to test the ECM. They can be found in old PC's or you can buy them on eBay. DO NOT try and probe the pins with the meter probes if you short the pins you WILL damage the ECM.



Drop the ECM, there are 2 screws circled in RED





Then probe the ECM as directed by the diagnostics. Pin 1 is at the top of the ECM as it is installed in the car. It is marked on the PCB but can be hard to see.

 

OK..just ordered some jumper cables...I will report back once I start to test.

 

When the instructions say to use the microprocessor lucar connector as ground, what are they referring to? The microprocessor seems to have a few different pins that are grounds?

 

Before you test continuity short your meter leads and either take note of the reading or if your meter has a rel function zero it out.

Then test continuity between pins 2, 6, 24, 36 and 45, they should all be less than 0.3ohms (not including shorted meter reading), then test pin 45 to car ground (chassis), if all of these are below 0.3ohms then use pin 45 as the ground for all tests.