I have recently had my AC compressor replaced so all new gas and hopefully no leaks. However, over the past week I've noticed warm air as I accelerate. Once my foot comes off the pedal it blows cold again.

This is Dubai with middle of day temps around 45 celsius and more- sometimes around 50, so the problem is very noticeable as it happens.

Does anyone know whether this could be a compressor problem - maybe the clutch isn't operating correctly or is this a symptom of low refrigerant - in which case I must have a leak. I hope it's the latter!

 

Just be aware that Jaguar and most car companies cut out the A/C at full throttle. This gives better acceleration but causes what you are seeing. I think everything is pretty normal.
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With respect, I think you'll find that Mid East specs require that the cold air supply must be pretty constant. I've had my S type from new, over 5 very, very, very hot summers with extreme temperatures like nowhere else on earth and also some pretty warm winters. Moreover, having driven 268,000 km in this car I do know what is normal and what isn't. Furthermore, if the AC drops for just a few seconds in these conditions the heat in the car becomes rapidly intense. Sorry to disagree but this is definitely not normal. One thing we do know about out here, whatever the car we drive, is whether the AC is working correctly. Frank

 

So the warm air gradually builds with throttle pressure or is it more like a switch - on/off?

Odd. How is your coolant level?

A R134 leak doesn't come to mind as a cause based on the symptoms, although a vac leak does - but this is more typical of older vehicles.

Care to post your year and engine in your sig? This can be of great help when troubleshooting.

 

The best way I can describe these symptoms is that if I accelerate slowly the air temperature will remain cool but if I kick down or even accelerate normally the air will blow hot - it's as though the compressor is playing 'catch up' with the engine revs. Once I steady the revs or if I take my foot off the pedal, the chill resumes.

The compressor was replaced recently (genuine Jaguar unit from British Parts) so the gas was topped up then - this problem has only manifested itself since that replacement. It did run correctly for several weeks daily use before this problem arose.

 

Hmm. I'm stumped - perhaps a pressure switch issue - maybe they put too much 134 in and when you give it the beans it overpressures the system... that is a bit of a guess.

 

I can't explain the behavior change (i.e., why this problem just appeared), however I can attest that my A/C compressor disengages at full throttle on my US-spec S-type R. Maybe cars for the Mid East market have that disabled, I don't know. It's possible that the mechanism wasn't working and the mechanic fixed it for you?

 

Interesting crt_ben....wonder if a TPS fault could contribute to the issue? I'd think that would throw a code though.

Maybe one of our electronics guru's will chime in.

 

I've had a closer look at the symptoms today and I must admit I now know that what I have described is somewhat inaccurate. While driving this afternoon I observed that it is actually the fan speed that is decreasing with acceleration and presumably no AC system malfunction.

I switched off the AC and the the fan speed continued to be inversely affected by the increased acceleration.

In mitigation for my non-observance of these new facts, in these high temperatures it is very easy to miss the blast of the air through the vents since when the air is hot there is no chill factor and the rapid temperature increase overwhelms all other sensations.

Presumably this now throws a different light on the problem? This is indeed getting curiouser!

 

Which fan? Engine, a/c vents, or ...?

I'm trying to remember what hot weather is like.......

 

Go here, you'll find out reaaaalllll quick


Bullhead City, Arizona (86426) Conditions & Forecast : Weather Underground

 

JagV8 - You're obviously in colder climes with the Yorkshire sun not beating in on you! There is only one fan that really matters when it comes to AC operation in hot conditions, whether in your car or kitchen....

I'll rephrase: As I accelerate, the ventilation fan that pushes the chilled air into the interior of the car via the vents 'tails off' from a full blast to a trickle thereby causing the inside temperature to rapidly soar.

Out here in summer, during the heat of the day and even with the AC set on low and working properly (i.e. so that the vent fan is on full blast) it is a major struggle to make the car comfortable - the hot exterior of the car, mainly windscreen and windows for instance (and even if they are tinted) will be too hot to touch from the inside, certainly on a short journey.

They are heat sources that radiate heat that 'battles' with the chilled air that is pushed into the interior via what are really quite small vents for the job that they have to do, especially to bring the temperature down as one is driving off. Once the 'battle' has been won by the chilled air, things become easier but in the early stages of a journey and especially if the car was not parked in shade, maximum ventilation is vital.

The bottom line is if the efficiency of the ventilation fan is even slightly off, hot will easily win over cold and the inside becomes an oven. Prolific sweat is then instant and the whole driving experience becomes rather like an extreme turkish bath - if you're a fat old fart like me it's even worse. That is an Arabian experience and one not often encountered in Yorkshire. Another good reason to fight global warming!

 

hmmm you did say that this was working fine for a few weeks when you first installed it. Leads me to think maybe you got a bad compressor. Just cause its new in the box doesnt mean anything. It sounds like a bad clutch on it.

but other causes could be.....

Possible Vaccum Leak in the system.

Possible problem with your charging system. Alternator, Battery, Cables, Connections.

 

Since I discovered it is the ventilation fan that is being temperamental I'm inclined to think it's a more general electrical problem concerning the fan. I'm going to go down that road to start, anyway.

 

The choices seem to be take it to someone who understands modern a/c & cars or start swapping parts (hoping to get lucky) or figure it out.

Here's how I'd be trying to figure this out. First, not much data so hunt for more. If it's cutting the vent fan(s), does it do it whenever I accelerate and no matter how hard/gently? From standstill and from other speeds? What does it do in Park if you suddenly change engine revs, or just maintain much higher than normal revs? When you let it go back to idle does the fan speed back up if it slowed down during the revving? See? Get data. I'm just thinking aloud how I'd try to get some.

Also, I'd be checking carefully as to whether it always or just mostly is consistent. Because if it's consistent then it's a control system choosing to do it (which would be in response to some input(s) making it see it as the right thing to do). If it's not consistent then either you've not seen the pattern or it's something like a bad connection (causing random effects).

Then... how does it work? - I'd read JTIS and about car a/c systems etc. There are at least 2 control systems: the a/c system and the engine control (PCM). Each has quite a few sensors and actuators. The systems hardly interact but they do a little. JTIS explanations and circuit diagrams are the guides.

I know that WOT usually cuts off the a/c compressor so I'd be sure to try acceleration that's nowhere near WOT. The PCM also monitors the hi-lo pressure switch, I think. And controls engine fan speed. I expect the engine fan(s) need to be on high for that climate so worth checking.

Another interaction is the power. Under acceleration the car uses lots more power. It needs it from the battery, I think, and will also load the alternator. That's going to drag on the drive belt, just as the a/c compressor does. Any of these parts may be the culprit and are worth checking. Maybe the belt slips. Maybe the battery is dying. Maybe the wiring is making a bad connection. Etc.

 

You could just come to my house.

 

What happens if you turn off the auto control and select fan and ac manually?

Does the fan still shut down?