Heater Valve Control Question
 

I was trying to figure out why it was taking so long for my cabin to warm up and found SERVICE TRAINING COURSE 703 JAGUAR CLIMATE CONTROL SYSTEMS. Trying to understand what I am seeing. It talks about a 12volt signal being cycled to the valve. I unplugged the valve and connected an analog multimeter to the pins on the A/CCM side of the plug to see if I was getting something that looked like the book described. Page 2.4.4 talks about a 6 second duty cycle and seems to indicate graphically that a 50% duty cycle would be 12v for three seconds and 0v for three seconds and that time varies depending on the temperature and settings on the control panel. Only I was not seeing 0 volts off and 12 volts on, rather I was seeing it cycle between 7 volts for a few seconds and 12 volts for a few seconds, or while the engine was warming up, it was just straight 7 volts. I ran it for a long time, tried multiple settings on the control panel but its always at least 7 volts with the fan on, even with heat set on High when the book seems to indicate it should be zero. Am I just not understanding the book or do I have some sort of voltage leakage through the A/CCM? Maybe 7 volts is enough to hold the valve closed, at least partly?

And with the valve disconnected from the A/CCM, I was getting 108° F out of the vents but it'll take hours to cool off enough to really test. I'll have to try driving tomorrow morning with the valve disconnected from power (default open) to see how quickly the temp rises from full cold (forecast 37° F in the morning) but thought I'd go ahead and post what I'd found just to make sure I'm understanding the book correctly and in case it helps someone else.

Multimeter is heavily averaging readinds and it is not fast. I used an oscillosscope to verify valve control. It is full battery voltage when engine is running. Controller is ticking current on off and off time increases towards cooler. It is continiously on when full heat and wise versa when cooling. Control is square wave and that can not be correctly measure with multimeter ac area.

According to the manual, the Heater Valve is not driven by a PWM signal (which would require an oscilloscope to measure) but by simple ON-OFF switching over a cycle of 6 seconds.

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The reason why the multimeter shows 7 V in the "off" state could be just some bias voltage of the electronic circuitry so that fault can be registered when there is loss of continuity in the valve solenoid circuit.

To test the ON-OFF signal contolling the valve, it is better to use a 5W bulb connected to the wires supplying power to the valve (I wouldn't use a bulb of higher wattage than 5W to avoid overloading the A/CCM).

Thanks. I wonder if someone who is tinkering around anyway and knows their heat works could test theirs the same way and see if they get the same sort of bias voltage, at least confirm what I am seeing is correct.

Although I think I have more problems going on. I think I should be getting a lot more air volume through the vents at max speed and I can't get much air out the floor vents at all. I just love old car problems.

There is no need for bias voltage.. When engine is running. Aux water pump is energized. That relay what feeds aux pump feeds valve too. As vale is just an coil the voltage is coing through it always. But this is just guessing.

The relay for the Aux Water Pump controls the pump only. The Heater Valve is controlled by the A/CCM directly:

https://cimg6.ibsrv.net/gimg/www.jag...135340260d.jpg

Oh you are right. I was so sure it was behind the relay. 🤪

Kind of threw me when I first looked at the diagram too but it really just shows that the valve and pump are grounded together. Summer before last I had a mouse get into the X308 and surgically cut 17 wires under the left front fender. Since that one wiring bundle had multiple identical wires, I had to trace ten of them to figure out how to reconnect . Everything I traced, the current was flowing back towards a control module, i.e. the computer was acting as a switch between the accessory and the ground. Here the computer is acting as a switch between the valve and the battery positive and so when I saw seven volts there and looked at the wiring diagram, I was a bit surprised.

I thought I fixed all the mouse damage (heat & everything worked last winter) but I first suspected the mouse had maybe chewed more wires than I originally thought. Still could be that I suppose but I never saw or smelled any evidence that the mouse had gotten inside the car or under the dash. I think I caught and killed the little critter pretty quick and plugged the hole in the shop building where it was missing the foam strip at the edge of the corrugated roof panel. Unfortunately, I've hurt my neck over the holiday and am not feeling up to anything that involves pulling the dash out or draining fluids right now. That'll have to wait till I feel better

Last two springs I've had this funny situation practically same as topic starter. Cabin does not heat up suddenly. Both times all it needed was slow engine rew up when driving. Thats it. It is cured for rest of the summer.

Vauxi, I read the climate control course that Pdupler linked. I knew that it would take a few minutes for the heat to actually start working. In the course it says that above 86* F the heat would then start to work in the cabin.

Since we’re talking about the heater, just in case someone didn’t know the heater electric pump impeller inside the pump is physically *not connected* to the electric motor. It’s actually floating and magnets are imbedded inside the plastic impeller. If you used a stethoscope and put it on the electric motor, you can hear the motor but may not have an impeller spinning.

I’ve often found the auxiliary heater pump to be the cause of low cabin temperatures on X308’s, it’s a very easy thing to repair if you’re able to or a very expensive item to buy new from JLR.

Addicted 2 boost: Yep I know. In my case engine temp was almost at operating temperature and it is still blowing only little warm air (at full blast of air volume). Outside temp was last time -5'c(23f), so it is pretty cold inside when it happened.. ;)

I put new brushes in the little pump motor a few years ago. I used to open the hood and whack on the little pump to get it started, then it would work great till next time. The old brushes were worn down to nubs. I can confirm that as of right now, the electrical part of the pump is whirring away magnificently. But because its only spinning a magnet around, not physically connected, I don't know if the impeller is also whirring away. Wish there were an easy way to check. I don't remember if the impeller was free-floating or if it was mounted on a bearing of some sort. I only remember working on the electrical part.

I don’t doubt the electric motors go bad on these but not as much as the heater core (matrix) calcifies shut in my opinion. I run mine full heat for a few minutes over the summertime and never had an issue.

Hello,

Perhaps a dumb question: were the heater valve and pump assembly get removed recently? The hose hookup under there is a bit ridiculous and it's possible to connect the hoses to the wrong outlets. Not saying that is the case with your car but I've seen it happen and the heater doesn't work right!
Lastly, the center vents don't always supply very warm air with the selector is set to the floor and dash vents position. Put the control the the dash vent and set the temperature to the highest setting. If the car is up to temp, you should get heat; assuming the system is working correctly!

It's kinda weird that sometimes if the outside temp is not very low, on my cars I really have to set the heat temp to a very high position to get heat.