Well I am on the road to fixing things already. Just got the car yesterday and it appears that the heater does not fully shut off. I new that the air cond . needed to be worked on but did not realize that I could not get outside air in through the vents. I don't know where to begin. I just hope and pray that the dash doesn't need to come out. I do love the car though. Any help to start me on my journey would be appreciated.

 

First thing I would check is that the heater valve vacuum line is attached. It's on the firewall, toward the right side. The default for the heater valve is open, vacuum closes it.

 

I just checked that valve. Seems to be working. It opens and closes when I adjust the heater control knob. I wonder if the hot air was just because it is so hot outside? It seemed pretty hot though. Could I be that lucky?

 

You need to add your vehicle details to your signature. There are numerous variations in models.

Which AC system do you have?

 

Was not aware that there was more than one air cond. system in the 95 XJS.
How do I find out? (Started to update Signature)

 

When you go through the various modes does the airflow change? I.E. on defrost, does the air go to the defrost vents? With the temperature set to full cold and blower on 2 you should have air to the vents, and set to full hot it should mainly go to the floor.

It's in the manual, but you can test to see if the blend door is moving between the heater core and AC evaporator by looking at the potentiometer voltages.

 

The Electrical Guide is here: http://www.jagrepair.com/images/Auto.../jvs1995en.pdf
See figure 23. It tells you the expected voltages on each pin for hot, cool etc. You can measure them on the AC ECU, which you'll find on the right side of the heater box. Remove the lower knee panel, the grill on the console cheek panel, and then slide the cheek panel out. You should be able to see the ECU then.

Be very careful when probing the connections for voltage to make sure you only touch one connection at the time, don't short 2 pins together with your meter's probe. It's easy to fry the ECU doing that and they are not available any more.

You're looking for the upper and lower feedeback potentiometer voltages and see if they respond as indicated when you turn the temperature knob from hot to cold.

If they don't, the possibilities are a bad potentiometer, or bad drive motor that drives the blend doors. The lower motor can be replaced reasonably easily, the upper is a dash out job, that takes most of a day to do.

 

If it turns out that you have blend flap motor problems try giving the servo a rap with an object before going to the trouble of removal. Testing indicated upper servo and potentiometer issues with my system but a couple of sharp raps with screwdriver handle freed it up. One of the fixings on both the upper servo and potentiometer are tucked in behind bodywork gusset and are not reachable with system in place.

 

Tomorrow I'm dropping the car off to get the air cond. recharged or at least checked. I ordered a shop manual too. Looks like I'm going to need it. When the weather cools down a bit I'll take a look at the heater controls. I had planned to get the seats re upholstered but I'm going to have to wait now to find out how much the heater controls will set me back.
Thanks for the info guys. It should get me started. I still love this car.

 

Your car should have Delanair Mk3

Here is trouble shooting guide. BE VERY CAREFUL probing voltage on the pins, if you short some of them you WILL blow the output transistors. Safest way is to use a small jumper plug on the pin with the other end connected to your DVM.

Like these, if you have an old PC you will find loads of these in there.

40 X 10 Female Female Jumper Plug Socket Jumpers Jumper Wires WS | eBay

Before you go diving into fault finding pull the dash side panels and check ALL of the connectors. Take a look at my blog I had to repair my AC and there is a few pics of some of the dodgy connectors.