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Determining Ambient Temperature?

ron in sc

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My workshop manual give specific instructions, in part it says:

“The pressures and temperatures specified in the below diagrams must be reached after approx. 10 mins. operation time at a speed of 2,000 rpm with the compressor switch on.” So I’ll have to get some to hold the accelerator at 2,000 rpm while I read the gauges.


The diagrams gives temps. for ambient. If ambient is temp measured about 2" in front of condenser that’s really not easily obtained due to position of condenser. It’s mounted sideways in an enclosed space. Or is ambient just the temperature outside?

Are the pressure readings generally done with the car at idle or does that just very with the auto manufacturer or with the compressor manufacturer?

I want to test the A/C system on my Porsche to see if the vent temps are within the range expressed in my workshop manual based on the ambient temps if I can get an accurate way of defining ambient temp.

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  • 1 year later...

ambient means "surrounding".

In the case of "ambient temperature", that means the temperature (use the average) near the rear deck lid condenser. Ignore the ambient around front condenser for test.

Simply take an accurate digital thermometer and place it 2" away from the deck lid condenser. You don't have to get neurotic, +/- a few degrees is fine.

Simply connect your ac services hoses to the compressor. Carefully route the hoses to the RH side of the compressor so they come out together in the RH corner. Carefully lay the deck lid down over the hoses, do not allow the deck lid latch to engage or you'll have a days worth of fun trying to unlatch it. You need the deck lid down so air circulates through the condenser. Start the engine. Turn the left hand ac knob (thermostat) all the way clockwise for max. cold. Turn the right hand ac fan switch to fan speed 2 for the test. I don't recall which fan speed the shop manual may have noted, however temps will be colder on fan speed 1 (slow) vs. speed 3 (fast). You may want to record the temps at all three fan speeds; allow a few minutes between each test to allow the temps to stabilize.

If you have a helper ask them to note the high and low side pressures on the service gagues while you rev the engine to 2k rpms. If you don't have a helper you could hang the gauges on an object high enough so you can see them in the rear mirror; caution: objects in the mirror maybe closer than they appear.

The best time to run the test is when outside temps are 80F or greater.

You can buy a reasonable digital thermometer just about anywhere, however a nice model is offered by Control Company www.control3.com , model Cat. No. 4339.

With this unit you can check the vent temps and since it has a nearly 10 ft cord you can place the probe in the evaporator to run some trouble shooting tests while you drive as well. Avoid an infrared thermometer, though they are good for certain tasks, they are not as reliable for measuring air temps.

Sorry for the late post, I fell asleep.

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