I now own a 1990 XJ40 Daimler 4.0 for a few months. After fixing many major things I’m trying to improve the airflow to the vents inside the car.
When I put the air speed to high, I’m only getting a ridiculously low amount of air in my opinion. (despite the loud/impressive fan noise coming from the dash) I get a bit of air from the footwell vents and the left and right head vents. The center vents do not work at all. (which i wouldnt care, if the other vents at least had some power)
I noticed the left AC blower has a flap which is always closed. When i stick my finger under the dash and push the flap in, i can feel a big amount of outside air rushing over my fingers.
Can I just stick something to the blower and make the flap be open all the times?
Note: the previous owner deleted the entire AC system for some reason. I got no AC lines under the bonnet nor a AC compressor. I could live with that if the outside air at least would blow with some force over my face. The last sunny ride with just 25C outside temp was rather hot and uncomfortable. Had to roll the windows down during the entire ride…
Pull off the wooden trim at the centre vent and remove any fasteners holding the plastic vent assembly. Push the vacuum operated flap open and insert a piece of rubber hose or other flexible material to keep the flap open.
Reassemble.
Now you will have air to the centre vent.
Oh - and check that BOTH blowers are actually operating!
Sounds like your drivers side blower isnt operating? Check for power on the brown with blue tracer that leads into the blower. It is powered 12v even with ign off.
The driver side one is definitely operating (left side, since im in Switzerland)
I pushed the flap in and noticed a big amount of air rushing over my fingers.
Also the old britle sponge like material on the flap broke off a bit and fell into the blower motor when i pushed the flap in. I definitely heard some of the material being thrown around in the fan.
Luckily the noise stopped after 10 seconds. (yikes)
I’ll try to get to the center vents and open the flaps manually and permanently like you suggested
I’m not too sure what you are referring to …where’s this “Ac blower flap” located? On the climate control itself? All I have is a flexible square section of rubbery tubing that leads from the blower to the climate control unit …btw my car is LHD also, but a 1994 model so possibe the design of the blower is different …pretty sure there’s no flap on the blower output on my car.
Im still a newbie so i dont know if im using the correct terms.
I removed the cover under the steering wheel. Therei could see many cables harnesses and behind them was a big black box (something called AC unit blower if i remember correctly. tomorrow I will make some pics.)
On the unit was a square with the sponge like material on top. I could press the square into the unit and it would bend in (spring loaded) and when i remove my fingers the flap would go back again.
I had the same problem and blocked the front vents partially open. If I want to block air from center vents I just close the manual curtains.
But…… if the car is cold the air that arrives to the front vents is very good. But when the engine temperature is raised the air partially decreases and I don’t know why. This happens if I select the temperature control to cold and the orizzontal control to the left (cold) . The lateral vents works good instead .
There is the mirror image of that box on the passenger side, as has been mentioned make sure that both of the motors are working, the fuses for them are in the footwells, the cover will have a legend to indicate which fuse to pull to disable one blower at a time. They are independently powered and if one is not working the air is divided between the opposite blower and the outlet.
The flaps on the blower motor that you are pushing in are to recirculate air within the cabin. Leave them closed and you will only get fresh air from outside.
Alright, to really simplify things think of your climate control system as consisting of four big boxes.
The biggest box (A) is square and holds the evaporator (basically a radiator), the heater matrix (basically a smaller radiator) and two rolling pin shaped “blend” doors. This big box is located behind the radio.
2 On either side of box (A) is a smaller square box. Each of these two boxes contains a blower motor that turns a squirrel cage fan and a vacuum operated flap door that allow the box to draw in outside air, cabin air, or a combination of both. Each box (a left and right one) has a hole in the side that blows this air into box “A” through a large tube.
Sitting on top of box “A” is a long narrow box which is actually the top of your dash. Inside this box is the center vent that’s right above the radio, the two side vents. and the two vents on the top of the dash (windshield defoggers called demisters).
That’s it … really pretty simple !! (There is also a small amount of air that’s directed into the footwells and to the back of the cabin through the center console but for this simplification we’ll just ignore this)
GREAT, now that you understand the basic system how does it operate ?
– The two fans blow air into big box “A”. This air is directed by the two blend flaps (remember the 2 rolling pins?) to travel over the evaporator (which cools it) and over the heater box (which warms it) according to the temperature setting and is then forced up into the long narrow box and finally exits through the three air conditioning vents or two demister vents.
So why isn’t my system working properly???
First BOTH FANS HAVE TO BE WORKING. Because of the design of the system if one fan fails you get almost NO airflow into box A. The fan sounds like it’s working like crazy but no airflow coming out.
It’s hard to tell if only one fan is running. To check this first pull the left fan fuse, if all fan sound stops the right fan isn’t working. If everything OK now push the fuse back in and test the right.
The evaporator has to get seriously cold, just a degree or two above freezing. To get good airflow the evaporator fins (remember it looks just like a radiator) must not be blocked by dirt and debris
The center vent and two demister door flaps (controlled by their vacuum actuators) have to be operating properly.to correctly distribute the air. If one or both of the demister vent assemblies has broken (very common) then a large amount of air will always shoot up onto the windscreen resulting in a greatly reduced amount of air coming out of the three dash vents.
To achieve the correct temperature the two blend doors have to be operating properly so the air can be correctly directed over the evaporator and heater. Even with “heat” selected the air is still passed through the cold evaporator to dehumidify it and then through the heater matrix (box) to warm it.
The blower flaps open when you select air recirculation which means the outside air will be blocked entering the cabin and the cabin air will be sucked back in the blower through that flap.
I’d check all the fuse boxes and relay modules for their solder joints. Clean all ground connections. That’s gonna give you a good starting point. In my case the R side blower stopped working because of a cracked solder joint in the R fuse box.
Closed? Or open? There is a vacuum operated flap that shuts off the outside air and causes the cabin air to be recirculated. If that actuator (#3 in this drawing) fails you will lose that functionality.
You can test the operation of the actuator in situ by selecting recirculate mode with the engine running and AC selected, or by disconnecting the vacuum line to the actuator and connecting an external vacuum pump (like a Mity Vac) and watching for movement of the actuator. One of my actuators failed as evidenced by an inability to hold vacuum and to keep the connecting rod retracted.
The vacuum operated vent door on the fan blower assembly determines where the air entering the evaporator box comes from, either outside air or recirculated cabin air.
If the vacuum actuator fails it fails to the outside air position. Why is this important? In the middle of a hot summer that means the evaporator is trying to cool down perhaps 100+ degree outside air verses already cooled recirculated cabin air. Major difference in what the evaporator can cool down.
Because I live in Texas and it’s WARM summer temperatures when I modified my climate control system among other things I disconnected the two fan assembly’s vacuum actuators and permanently sealed the vent doors open to cabin air. This way I was always assured of providing the evaporator the coolest air possible. There is enough leakage of fresh air coming into the cabin from the doors and windows that I’m not worried in the least of the air quality.
I managed to take the mid vents out and stick something into the flap to make it permanently open.
The airflow is decent now, im already happy! Especially on the highway the airflow is quite adequate now.
Thanks all for your help. Maybe now It could be interesting to add a functioning AC system back into the car. (i heard the cooled AC air goes trough the center vents as well )
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