Facelift Air Conditioning - Can it just not cool well on hot days?
 

I have a 1996 XJS with the AJ16 engine.

It’s been hot here in the DC area. Hot and humid. Over 90F (or 32C for the friends overseas) and I can’t get the air coming out of the vents to come out any colder than 70F (21C). Is that what this system can top out at?

The system seems charged. At idle, the low side is about 40psi. The compressor seems to run, but the high side stays at about 170psi. It never seems to click off, the clutch is spinning, and I believe it’s trying to cool…but it never gets cold.

When I get on the gas (in Park) the low side drops, but not the high side. That seems to stay constant…more or less.

I had this system vacuumed and recharged by a shop maybe two years ago? Frankly, the AC has never been great over the years I’ve owned it.

This morning, it’s 80F outside and the air coming out got down to 47F. So the system is working.

Vee, your compressor may be weak. Or maybe your aux fan has gone bad.

Of all my vehicles my XJS has the distinction of cooling the coldest- once it does get there. For example;

If if I take the car out from a garaged space, even if it’s 105 out, the a/c will cool excellent immediately, however if I need to park somewhere outside and the car ends up sitting in the heat, it takes maybe 10 minutes of driving for the car to be able to cool again, where my other cars take only 5. Of course traffic, etc will all affect results, but when my car cools, it freezes. It just takes longer to get there....and in extreme traffic- the kind where you sit for over 10 to 20 minutes- I don’t know/think of any XJS AJ16 than can manage that.

The aux fan is running, so that's that.

I'm thinking it may be the compressor. It's running fine this morning, but when it gets hot, like it has been, I can't get it cold. Not in city driving, and not in highway driving. All well over 10 minutes of both. Car is garaged at work, so it wasn't baking in the sun either.

There was definitely a difference when I pulled the AC relay, the clutch definitely let go. Once I put it back in, I heard the click, but the air out of the vents never went (meaningfully) below 70F.

Also; Can you describe your driving? Like, are you typically getting into the car when it’s been sitting outside in 95+ weather and immediately getting into heavy traffic?

If thr car just won’t cool under any circumstances then I bet your compressor or aux fan are the problem as I said above. You could also be having issue where the heat valve is staying open and cold air is mixing with cold air.

Any local rebuild shop should be able to rebuild that Sanden compressor. If not, make sure you don’t grab one of the cheap ones of EBay.

EDIT - you answered what I wa asking before I posted this

Driving in this morning, air went down to about 42F!

Not sure why it works now, but not when it's really hot. That's why I was wondering whether the car responds differently under severe heat.

Is there an easy way to check that heater valve? What about the AC Expansion valve? I don't believe I ever replaced that. I did on the previous car, but I don't believe I ever did it to this one.

Thanks.

well it’s going to be easier for a system to cool when it’s not so hot outside. Even a weak compressor can manage that....unless today was different than every other day

The heater valve you will have to physically look at and see if it’s shutting down when you turn the A/C on

TBH, I have done some hacks in my car that I am not proud of since I am all about having things working as intended.

My heater matrix is disabled. No water goes into it at any time, hence I have no heat. I am in Texas, car is a weekend driver and I never turn the heat on on any car anyway because it does not let me breathe. But I have the complete assurance no hot air is mixing with the cool air

I shut down the vents to the “rear seats” completely.

I put the vents in the mode where all the air comes thru the vents and then disconnected the servo, so it’s always blowing all air thru the dash vents


I am pretty sure more “modifications” where done that I just can’t recall. At some point I will revert all these things so the car works as intended, or at least some of them, but what can I say? A man gets desperate when it hits 105....the only modification that is definitely going to stay is plugging up the vents to the rear seats. That’s just unnecessary

How old is your compressor?

Try pulling out the LHS knob and turning it to full cold. This over-rides the aircon thermostat and if the system is working properly, will freeze you very quickly. If it does not, you certainly have a problem. If you do have a problem, nothing for it but to have an expert go through the system and find which bit is not working. Not that complex on the mechanical side: compressor compressing? gassed up? condenser free of rubbish? dryer drying? expansion valve working? . After that it is under-dash work and the electronic controls - more complicated...

Thanks. I am fairly confident that the condenser and the drier are working, as they have been replaced in the last few years.

The refrigerant is certainly at charge.

While the compressor appears to be working, I can't be sure if it's performing, but I'm going to table that for now and move it lower to the list.

The expansion valve could be suspect, but without a leak, I don't understand how that part can fail. It doesn't appear to be a common failure point on these forums, unless it had sprung a leak.

Lastly, I wonder if there could be an issue with my heater valve? Is it plausible that it could be at fault? I have two questions.
One is whether or not it would make sense to add a manual valve to block off all coolant the heater matrix either as a test, or in the summer months in general?

Two, I will have to check for a vacuum at the hose connecting into this valve next time the AC runs warm? I'm not sure that the presence of a vacuum doesn't prove a failed valve. These things are cheaply made and although I've replaced it in the past, the first one I got leaked like a sieve. I did get it replaced, but I suspect they're all crap. I'm leaning towards replacing it with a plastic one that has been recommended in the past on these forums.

As a test, with the car stationary and the AC running try spraying the condenser with a garden hose. If you get cold air then, the problem is airflow over the condenser and it can't shed heat effectively. Is the foam strips around in the radiator in place? So all the air is forced through the condenser/radiator. Fan clutch is good?

Water valve: if you turn the temp knob to full cold, the system - if working correctly - will close the valve. Note the valve actuating arm's position, dial up full cold, and see if the arm moves to close the valve. If it does not, then either you have a stuck valve or no vacuum in the actuating system to close it. You should see a vac tube going onto the valve, if it is not there, or perforated, that could cause the problem, as could lack of vacuum source. Also you can manually close the valve and somehow tie the arm in the closed position, or fit a manual valve and just close it during the and see what that does for the temps in summer.
New valves are available, and FWIW, I think keeping the system working as OEM is worth doing, it works really well if working properly. But, to repeat, first try the manual control of pulling out the temp knob to the "click" and see what that does.

I assume my x300 will share most AC components with your XJS. At 21C outside with the air con at 3/4 front(when its generally coldest I think) it should get uncomfortably cold inside your XJS after a while and by the way your XJS is half the size of my LWB inside. It certainly the case with A/C on mine so yours should be as good if not better. Obviously older XJS with possibly still R12 shouldn't be compared here, they will be cooling much better anyway.
Sounds to me like you have a clogged system if the AC is fully charged as you say.

170 psi on the high side isn't enough for R134a. You should be seeing 210 to 260 PSI. Since your low side is dropping and the high side is the same you are most likely slightly under_charged. Start adding a bit of r134 with oil and see of the high side starts to drift up.

Had this problem too. Replace filter / dryer and it is again a refrigerator in the car at 35 ° C + . Also with my X300 faster cold after replacing filter / dryer

Thanks for the help.

Im away from the car for a few weeks, so it’ll take some time for me to get this under control. The drier has been replaced recently....so I don’t believe that’s my problem. I’m going to do some heavy investigating on the heater valve.....

ill update in a few weeks....

That's an idea. I have read it should be replaced each time the a/c system is opened up, and I know my system has been opened up without replacing it. And it's fairly cheap and easy to do, I gather. Good first step.

The reasons for that is the hydroflurocarbons (i.e. refrigerant) are reactive to water, and they form hydrofluoric acid when combined with water. The idea is the dryer contains a decessant (like silica gel) to absorb and retain any water. When the system is opened up and humid air is allowed in, water can enter the system and possibly be more than the dryer can contain. Of course, this assumes that the new dryer has actually been sealed against the atmosphere since manufacture and the decessant is actually not saturated with water already. I'm doubtful how many are actually installed in that condition.

Ha. Well, it's something to keep in mind anyway. My own aircon is temperamental: sometimes the compressor clutch plate clicks into position, sometimes it doesn't. I find if the air's tepid I can make sure it works by switching to Defrost until the hot air comes out by the windscreen, then switching back to cooling. When it cools, I wouldn't call it ice-cold or anything, but it's certainly enough for a Japanese summer.

Where exactly is this? If you have a photo, that would be really helpful. I'm not quite sure where to look.

Here's a pic of the valve. You can see the external actuating arm

https://cimg5.ibsrv.net/gimg/www.jag...f0ecc6ca31.png



Cheers
DD

Okay, I think I see it. This looks about right.
https://cimg6.ibsrv.net/gimg/www.jag...20d635d156.jpg
Not sure how easy it will be to see the external actuating arm move, mind....

https://cimg2.ibsrv.net/gimg/www.jag...db42e4cc9b.jpg
Probably easier to go by feel....
So the test is to see how far up that arm moves, I guess.