Is this common?

I notice it much more now that it's cold outside... When I start the car and let it idle to warm up with the heater fan on full blast, the airflow is significant. When I start driving and leave the fan on full blast, the airflow is significantly reduced. Unfortunately, this seems to render a cooler ride during the time when I want a warmer ride.

 

Is this normal HVAC system operation in an XJ8?

 

FWIW my older X300 does the same. I always assumed it was the speed sensitive feature of the fans.

On my car, at least, the difference isn't too great if I have the system set to "Auto". Howevr, if any of the manual setting are used the difference in fan speed is much more pronounced.

Others will schime in

Cheers
DD

 

Doug, now that you mention the Auto selection not doing that, you're correct...

When Auto is selected, it turns on the A/C first, regardless of temperature. It will engage the A/C if it's 8*F. Is that normal? If so, why does it do that?

 

My '00 XJR does the same thing when the system is not on AUTO mode. Indeed it is due to the speed sensitive nature of the fans. Ram air when on the move will cause less electric motor intervention to spin the squirrel cages. And yes, a bit of an annoyance on very cold mornings!

 

That is annoying.

Does yours go to A/C when Auto is selected, even when the temp is set to 80*F? Mine does.

 

Normal, and common with climate control systems, for the "A/C" to operate even when heat is called for. This is to dehumidify the cabin air for comfort and has the additional benefit of keeping the glass clear. You can manually defeat this if desired, of course.....a feature that older Jags didn't have :-)

Leaving it set to "Auto" and just letting the system "do its thing" gives good results for most conditions but when I want something different I often feel like I have to browbeat the system into compliance. Sometimes with automatic climate control systems the designed-in electronic "logic" seems at odds with my designed-in human logic.

To be honest I'd be perfectly happy with a fully manual control system. Twistng a couple knobs to adjust temp and airflow isn't beneath my station in life, even in luxurious car.

Cheers
DD

 

One of the things the system *should* do, when cabin warming is called for, is defeat the fans entirely until there is enough engine heat to actually warm the air. This is to prevent that cold blast at a time when you least want it.

I'm glad you mentioned this because that feature needs tweaking on my car and I keep forgetting to research the situation.

Until a recently I could reliably predict this event. It would happn while waiting at the first stop light about a mile from my house. Now, though, the fans are kicking on way too soon....after driving less than a block....so the system blows cold at at me!

Cheers
DD

 

Maybe check the temp sensor next to the steering column behind the little grill. It can be dirty, or the little fan may not be working properly. There is a thread regarding cleaning it in here somewhere. My XJR was very good about not turning on the fan until enough temp had been reached. I don't remember if the XJR did it, but my Land Rover will allow Auto Setting, then hit ECON and it turns off the A/C but still auto controls the temp.

 

My '99 Jeep Grand Cherokee Limited never did that and neither did my '06 BMW 330xi. When cold, they always went to defrost. None of my parents' vehicles ever did that either. This is definitely the first vehicle I've seen choose A/C when 8*F outside and the temperature on the vehicle's console set to 76*F on the AUTO selection.

I wouldn't mind a manual control system either. But it would annoy the hell out of me if the fan speed decreased when driving.

 

And, when in "defrost" go look in the engine bay of those cars and I bet a dollar to a donut you'll find that the A/C compressor is engaged....even if nothing on the dashboard is telling you so :-).






Maybe it's the first vehicle you've seen where the system *tells* you the A/C portion is active with a little red light on the button. But, it's not the only vehicle that engages the A/C when heating (or defrosting/defogging) is called for.

"Air conditioning" is usually thought of only for refrigeration purposes but it really does "condition" the air by dehumidifying it....even when heating is called for.

Cheers
DD

 

I understand the defrost utilizes the AC compressor, but it's on defrost, which would be ideal at 8*F. It's a bit odd.

 

Well, Jaguar does sometimes have odd ideas :-). In this case, perhaps, it's having the "A/C" indicator light glow when cabin heat is called for.

But I guess I'm not quite sure what you ARE expecting.

However, I can assure you that Jaguar is not alone in using the "air conditioning"/compressor/refrigeration system even when cabin heat is called for. As I say, it's for dehumidification.

When is the last time you saw a luxury car driving around around with fogged up windows ? :-) :-)



Cheers
DD

 

Good suggestion. Actually, I've cleaned the little aspirator fan fairly recently. But....that doesn't mean the sensor is reading correctly.

Worth checking.

Cheers
DD

 

There's also the benefit of running the compressor to lube and keep it from drying out during the winter months.

 

Is there a way to disable the speed sensing fan? This thing's heat SUCKS when the car is moving in the cold. We've been below zero at night and in the single digits during the day.

My wife goes out in this car and our 11 month old son is with her. I don't give a **** about dehumidifying the air, I want LOTS of HEAT when driving. My 1986 Ford F250 diesel farm truck has far superior heat than our car. That just sounds wrong.

 

No way to disable it as far as I know.

I've been meaning to research my own heater problem. I'll try to do that soon and report back if I come across anything.


[/quote]My wife goes out in this car and our 11 month old son is with her. I don't give a **** about dehumidifying the air, I want LOTS of HEAT when driving. My 1986 Ford F250 diesel farm truck has far superior heat than our car. That just sounds wrong.[/QUOTE]


Over the years there have been complaints from some (me included) regarding weak heater performance on the X300s.

On all three of my Jags, the X300 being the worst, I concluded that the system is designed to heat passengers when they're cold much more gently than it cools them when they're hot. But, in all three cases the system can be browbeaten into performing reasonably well by manually driving the temperature selection wayyyy high (or even uo to "maximum") and selecting max fan speed.

I also wonder if there's an actual correctable fault in your case. Perhaps the electric heater pump isn't working? You can put your hand on it and feel it operate.

Or perhaps the thermostat is faulty and not allowing the engine to reach normal temp as it should?

Cheers
DD

 

All these complaints echo my thoughts regarding the system in my car too. The heat is basically the only thing I dislike about the car. A/C is fabulous, heat is rather lousy.

What I have found, although it goes against conventional wisdom regarding [not] letting a car sit and idle to warm up when it's cold outside, is that if I go outside in the AM, start the car and let it warm up for 10-15 minutes with the heat on, it'll be nicely warming up inside when I come back out and head to work. If I start driving right away, the car seems to take forever to warm up (and yes the t-stat is new). Sooo, if it means that I'll have a comfortable drive to work in the morning, I'll let my car warm up before setting off. After all, it gets maintained to an **** degree since I work for a JLR dealer so it can handle a bit of extra 'stress' in the morning!

 

bergxu, we do the same thing. Why against conventional wisdom? It's a gasser, not a diesel.

 

IMHO conventional wisdom is a throwback from the old days.

Way back in the day when most cars had carburetors you didn't wanna start a cold engine and walk back inside for another cup of coffee because the engine would be left running "on the choke".....and possibly washing down the cylinders with an overly rich mixture.

Not an issue with fuel injected cars where cold enrichment is gradually and automatically reduced. No need to shove a manual choke knob back in or kick the throttle to disengage an automatic choke.

Cheers
DD