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a/c slow to cool

Posted: Sun Aug 05, 2018 12:31 pm
by jruthroff
I have a 1987 Jaguar XJ-S V12. THe original a/c system...all but the evaporator...has been removed and replaced with a Sanden compressor, new hoses, new dryer/condenser and new expansion valve (all R134 parts). While this system "works", it leaves something to be desired.

The biggest complaint is the amount of time it takes from engine start until I actually get cool air. In my other car, a 2007 Camry, I good pretty cold air within 10 seconds of turning the AC on. In the Jag, it's more like 3-5 minutes. It also could be producing colder air, it now bottoms out at about 53 degrees F.

I have a gage set, but am not convinced of its reliability. It reads about the same on the high and low pressure sides which, from what I read, could indicate a refrigerant leak, OR a failed compressor (or possibly both???). I would think that if the compressor was broke it wouldn't cool at all, and if there was a refrigerant leak that the cooling performance would steadily worsen, but that doesn't seem to be happening.

Thanks in advance for any ideas/input.


Re: a/c slow to cool

Posted: Sun Aug 05, 2018 2:37 pm
by bohica2xo
If you have a gauge set and the high side is the same as the low side, one of two things are true.

1) You have both handwheels open. This is not how you use a manifold set. The handwheels must be closed.

2) Your compressor is not pumping. This could be either a compressor that is not spinning, or an internal mechanical failure.

Ignore the used car dealer trying to tell you it is a TXV. We call him the bad advice troll.

Re: a/c slow to cool

Posted: Sun Aug 05, 2018 9:30 pm
by JohnHere
What are the pressures, by the way? Re-test with the A/C turned on, compressor running, engine speed at 1,800 RPM, windows open, blower on high, and handwheels on the manifold gauge set closed as bohica2xo mentioned. Post the pressures here.

Re: a/c slow to cool

Posted: Mon Aug 06, 2018 6:03 am
by Cusser
jruthroff wrote:I have a 1987 Jaguar XJ-S V12.

You sure these Jaguars were engineered well as relates to AC in those days ?

Re: a/c slow to cool

Posted: Mon Aug 06, 2018 11:43 am
by jruthroff
A preliminary comment, as I said in my first post...there is nothing remaining of the original Jaguar a/c components except the evaporator. The compressor is a Sanden, the evaporator and drier are from Vintage Air, as, I think, is the condenser. Everything other than the evaporator have been replaced.

Under the following conditions...ambient temp 88 degrees F, a/c on, windows open, compressor engaged, gage knobs closed, engine at operating temperature, and blower on high, both sides read 85. This value does not change on either the high or low side when RPM is brought up to 1800 RPM.

This vehicle has dual electric fans, and both are running during the test.

Again, it does cool, but slowly and it never really gets cold.

Additional information...I have pulled a vacuum on it, and the vacuum holds overnight, so I would not think a leak is responsible...but if I did know what was responsible I wouldn't be here asking :-)

Help/comments appreciated!



Re: a/c slow to cool

Posted: Mon Aug 06, 2018 2:26 pm
by bohica2xo
It is difficult to get cooling with zero differential pressure.

You mentioned the gauge set before, thinking it may be unreliable. If you can borrow one from the local chain auto parts store you can reduce that variable.

But there is also the possibility that your service valve connectors are not depressing the Schrader valves on the car. This is common with aftermarket 134a adapters. What happens is the ball lock connector over travels a little bit, tapping the stem on the Schrader valve when you first install it. This lets a little pressure in to the hose, and provides what is basically a static pressure reading. You never actually see a system reading on the gauge.

That situation can also make charging difficult. A Schrader valve will work like a check valve - you can push some refrigerant past it, but when the flow stops all you are reading is the static pressure of your test hose.

And of course if you evacuate the system with closed couplers, evacuation does not go well either...

How did you charge it, and how much was charged?