I drive a 2012 XK convertible. While there appears to be nothing wrong with the A/C, it is very slow to engage....sometimes 5 minutes of driving before the compressor kicks in. It is always slower when the engine is warm. I read somewhere that the A/C is engaged via some sort of pressure switch? Anyone have either the same experience, or a suggestion to cure this?

 

The compressor is always on as it does not have a typical clutch. The freon is controlled by a pressure valve . When starting the car after sitting in the sun and the AC switch is on or in AUTO mode it usually takes a minute or two to push out the hot air in the ducts. Once done you should be getting cold air. If you are not experiencing this you may either have a bad valve or you are low on freon. A dealer or AC shop should be able to find the problem.

 

Isn't there an O-ring or something small somewhere that causes problems?
Or maybe that is just for the hissing-squealing noise.
Maybe ignore this post.

 

My 2012 XF did this one day last week after work. It just blew slightly cool getting out of the parking garage and I was nearly out of downtown before it suddenly kicked in and blew full cold. Its been normal before and since. I'll be curious tho to read any further posts in case it happens more frequently. Hopefully somebody knows exactly what the cause and fix is.

 

Thanks....I suspect the pressure switch as it is far too long for just blowing out the warm air. I also notice that it seems to require revs to get it active.... once I get up to any decent speed it will kick in, which implies pressure.

 

If the pressure switch is bad, it needs revs to get enough pressure to push freon through.


Ive changed my pressure switch. highly likely this is your issue

 

Folks should remember that no A/C system is completely leak proof over a period of many years. My BMW's also have Denso's, and BMW specs a 150 gram normal operating loss over 5 years. Here's an example on one of my cars.

BMW's full spec is 780 gm on my 530 system. I evac'd my system for the first time at 12 years. The evac system sucked out the remaining 300 gm, meaning I'd lost 480 gm over 12 years. The loss spec would be 150gm * (2.4 "5 year periods"), or 360 gm. So, mine was slightly worse than spec. Reinjected 780 gm, plus the correct oil spec. Works like a champ.

So if you're 8-14 years in, you're likely to be down some (note I don't know Jag's "normal" loss spec). The right way to fix it is a evac and recharge. Correct Freon is measured by weight, not by pressure. My pressure was pretty near normal on the guages, even at 40% of correct freon weight.

Canned parts store freon is not the way to recharge an AC system. My DIY garage guy charges $75 for a recharge, and I work with him as it's done (hence the data above). Any competent Euroshop should be able to do it; absolutely no need to go to Jag for an overpriced service.

I'll probably do the Jag this summer, just to get it done.

 

I stuck a thermometer in the center dash vent and have been watching it for several days. Normal operation seems to be to drop 20 degrees in the first minute after starting the car, by which time I'm starting to feel the cool breeze. It will bottom out about 50-55 degrees below the outside air temp after about 5 minutes. On Friday after work, needle didn't move at all for the first two minutes, but once it started moving, it plummeted pretty fast, pretty much like normal, bottoming out at 43 degrees F (outside 96). It'll still freeze me out of the car and fog my sunglasses by the time I get home from work, just occasionally takes a couple minutes to get started. I won't have any weekends free to mess with a DIY repair anytime soon so will probably have to go to a local indy. Of course if I took it in, Jeff will put a 100 miles on the car, keep it for a week and tell me that it won't exhibit the symptom for him. But wondering if its one of those things that will be more expensive to fix if I let it continue, do I need to fix it right away or is it safe to wait till it happens often enough that they can't help but experience it.

 

Do our cars post a code if the pressure switch is bad?
On my other car, I wasn’t getting any cold air, and read that the pressure switch was a common failure on that car. Normal OBD reading showed nothing, but reading extended modules showed a code, which meant ‘pressure switch open circuit’, so the pressure switch wasn’t working. Bought a generic replacement switch (original was Denso), released the coolant, replaced the switch, recharged, and now have cold air in that car.

 

If you are getting 40-45*F air out of the vent it is the normal level . What do you have the temp set at? another common problem is the mixing valve/flaps in the auto AC system. If the heat flaps aren't working correctly or the sensor for mixing isn't working correctly it will let heat mix into the ducts causing higher temps. Your AC guy should be able to check this. I assume he would check this before draining and refilling the system.

 

It's not the freon. That's the first thing I tried.

 

Well for this "testing" the past week, I've had it set full cold, latched re-circ. Although this morning was cloudy and much cooler outside and I couldn't take the full antarctic mode. I dialed it up to 72 on the way to work. I'll watch it the rest of the week on that sort of medium setting and see how it responds.

 

72 is a good setting which will exercise the blend flaps . Then again if it is 80 out and you get warm air then you have a problem. Good luck

 

Your had it recharged? Do you know what the weight of freon removed was? Also the recharge weight? Useful info to know. I found .7 KG, or 700 gm as a recharge weight online. Couldn't find the refrigerant oil spec.

Gauging it looked good, even as I was down more than 50%.

 

So......it turned out to be the Compressor in the end. Clutch was not engaging on demand, sometimes yes, sometimes no. Compressor was weak and not long for this world, so has been replaced. Unfortunately, this was the most expensive solution, but that's life with a Jag......

 

true enough…. Or, 10 years out of an air conditioner compressor while located in Texas, isn’t all that bad.
Related, I rarely get 10 years out of a refrigerator compressor before needing service. My German Liebherr (touch wood) has lasted the longest at 8 years, thus far.

 

These Denso compressors don't have clutches, as you've known them on earlier AC compressors. They use a variable swash plate to adjust compression. Not clear what your tech meant by "clutch not engaging on demand" because there isn't one. The pulley has a set of internal rubber bumpers that cushion rotation forces, but that's all.

Was this a dealer, or an Indy diagnosis?

Everything you always wanted to know about Denso compressors, etc:

https://youtu.be/T6TpXZIFzwU

 

The pressure switch would have been a cheaper first option to try, especially as it is a know issue with these cars, but at least it is sorted.

I had a 1000km road trip over the weekend and mine is still not right. Pressure is good, evap temperature is good (0-2 deg C) but although I had the controls set to 18 deg C the interior was at 24 deg C.

I found that dropping the passenger side to 16.5 deg C kept the cabin at an acceptable temperature.