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Old 08-21-2009, 03:44 PM   #1 (permalink)
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AC system was flat empty so I put in 24 oz and checked it, that brought it up to 40lbs even though the system holds 34 oz. It blows cold but after a couple days it started cycling on and off with the pressure bouncing between 35-45 as it cycles.


This is on a 99 SE with Duratec.
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Old 08-21-2009, 09:31 PM   #2 (permalink)
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It is normal for AC compressor to switch on and off.

"Flat empty"? You mean no pressure at all?

Normal lo-pressure for summer is 40-60 psi.
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Old 08-21-2009, 09:43 PM   #3 (permalink)
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It will cycle on and off. It's normal.
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Old 08-21-2009, 11:41 PM   #4 (permalink)
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QUOTE (Millermagic @ Aug 21 2009, 10:43 PM)
Quote:
It will cycle on and off. It's normal.[/b]

I understand that. I should have clarified, its cycling on and off every 1-2 seconds, continuously.


QUOTE (paker @ Aug 21 2009, 10:31 PM)
Quote:
It is normal for AC compressor to switch on and off.

"Flat empty"? You mean no pressure at all?

Normal lo-pressure for summer is 40-60 psi.[/b]

Yes it was empty. I put a key into the port to see if there was anything even there and it hissed out in a split second. So I added one 12 oz can and it kicked on once or twice, then as I added the 2nd 12 oz can it started running regular. I had a mechanic there and his guages showed a correct charge, then after a couple days it started cycling so I checked the charge but it doesn't appear to have leaked.
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Old 08-22-2009, 11:59 AM   #5 (permalink)
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On a 1999 Taurus, at 80 degrees F and at sea level, Low Side Gauge pressure should be 22 to 45 psi and High Side Gauge pressure should be 125 to 230 psi.

Consider replacing the A/C Clutch Cycling Switch, if the system is properly filled. I had to replace this switch on a new Motorcraft accumulator I installed on my 2000 Taurus in April. It was cycling incorrectly and causing the unit to freeze up. Sometimes, even new parts are bad. Just unscrew old switch, coat threads of new switch with PAG oil, and screw on.
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Old 08-22-2009, 12:50 PM   #6 (permalink)
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QUOTE (topgunovrtx @ Aug 22 2009, 11:59 AM)
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On a 1999 Taurus, Low Side Gauge pressure should be 22 to 45 psi and High Side Gauge pressure should be 125 to 230 psi.

Consider replacing the A/C Clutch Cycling Switch, if the system is properly filled. I had to replace this switch on a new Motorcraft accumulator I installed on my 2000 Taurus in April. It was cycling incorrectly and causing the unit to freeze up. Sometimes, even new parts are bad. Just unscrew old switch, coat threads of new switch with PAG oil, and screw on.[/b]

Where is this switch located?
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Old 08-22-2009, 01:55 PM   #7 (permalink)
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On the accumulator/drier.

To me, it sounds like you have a leak. The system will still have enough pressure to "hiss" when you hit the valve with a key, but may not have enough to run. Next time, use a can of refigerant with dye in it so you can find it.
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Old 08-22-2009, 02:07 PM   #8 (permalink)
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QUOTE (00tec-saTX @ Aug 22 2009, 02:55 PM)
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On the accumulator/drier.

To me, it sounds like you have a leak. The system will still have enough pressure to "hiss" when you hit the valve with a key, but may not have enough to run. Next time, use a can of refigerant with dye in it so you can find it.[/b]

It definately has a leak, hence how it became empty before. And I did put the can in with dye in it.

As for the purpose of this thread however, my question was in regards to the compressor cycling while on a full charge, because the system is holding the charge at this time.

Once it leaks enough to lose pressure, I will address that problem separately, but thank you for your concern.
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Old 08-22-2009, 05:44 PM   #9 (permalink)
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How did you determine that the ac system has a full charge?

You did not mention the high pressure reading, so I expect that means you don't have an ac manifold gauge set.

If the system was empty, and you installed the contents of two 12oz cans, how could the system be full, if the stated capacity is 32ozs?

If you read the pressure with one of those cheap little gauges they come attached to cans of R134a, I hate to burst your bubble, but you still have no idea of what the pressure on the low side is, because the cheap can gauges are horribly inaccurate.

While the low pressure switches located on the accumulator do go bad, they usually will not close the switch to allow the ac clutch to engage. I have never seen one that would cause the ac compressor to cycle on and off. For instance, when I bought my 96 Taurus Wagon back in 2001 with 103K miles, the AC system was not working. After determining that the refrigerant level was low, I added refrigerant, but the ac clutch would not engine. Even after bringing the refrigerant level up, the ac clutch still would not engage. Jumping the low pressure switch allowed the ac clutch to engage, and the system to work. Replacing the the low pressure switch fixed the problem permanently.

Most probably the refrigerant level is still too low (the cause for most ac system cycling problems). The low pressure switch is working, since the ac clutch does engage.
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Old 08-22-2009, 07:32 PM   #10 (permalink)
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QUOTE (gohim @ Aug 22 2009, 05:44 PM)
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How did you determine that the ac system has a full charge?

You did not mention the high pressure reading, so I expect that means you don't have an ac manifold gauge set.

If the system was empty, and you installed the contents of two 12oz cans, how could the system be full, if the stated capacity is 32ozs?

Most probably the refrigerant level is still too low (the cause for most ac system cycling problems). The low pressure switch is working, since the ac clutch does engage.[/b]

Thanks for your input. As I stated in one my posts, I did have a mechanic there, his guage set readings were 40 on the low and if memory serves correctly it was 210 on the high side.

Sure its possible that the system is low, however the mechanic recommended I not add another can because he claimed 40 psi on the low side is a full charge, and the reading is now flucuating with the cycling but 40 psi is still the low side average.

The a/c still blows as cold as before, only symptom of anything is the cycling.
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