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Discussion Starter · #1 ·
On my 2000 mustang, the A/C was blowing warm air, so I bought a bottle of that AC Pro at walmart, followed the instructions exactly and it still blows warm air! WTF? Is the AC compressor supposed to engage and spin constantly or is it supposed to engage/disengage every few seconds? Mine is doing that so I dont know if that's a problem or not. What else would cause it to still blow warm air? I put about half the can in and stopped because the gauge on the can was in the max normal range. Any thoughts?
 

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Start and idle the engine and turn the ac on max. The compressor should engage. The amount of time it stays engaged will vary but it should stay engaged for at least 15 seconds or so. If it only stays engaged for a few seconds then your refrigerant charge is likely still low.
 

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Discussion Starter · #3 ·
So it should never run constantly?
 

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agree with blulakr, you need more refrigerant, yes it should stay on in max.
 

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No, it only runs intermittently, if it ran constantly it'd probably freeze up your evaporator.

If you get the air cold enough you freeze the moisture out of the air and turn the evaporator into a chunk of ice that can't flow any air, so they cycle to keep the air at optimal low-temp.

Low pressure can also make it ice up, because you've got less pressure on the low side, and around the same on the high side (it's throttled) so more liquid turns to gas, dropping the temps too low.

Needs more refrigerant. If you can find a friend with a pressure manifold it's typically a lot more accurate than the 50 cent gauges they put on the cans.
 

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If its blowing warm air because it needs refrigerant it should take at least one to one and a half cans to get going cold again. The other thing is that since it ran empty it could be airlocked. Sometimes the system needs to be vaccumed out first then charged.....I always bleed remaining pressure off with a long screwdriver before I refill and have had good luck so far....so far! Try making sure you have at least one can in first then go from there. Is it the big or small can?
 

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So it should never run constantly?
Actually sometimes they will. It depends on the pressure in the system. When the low pressure side of the system gets down to around 25psi the compressor disengages. This keeps it from icing up.

If it's really hot outside the system pressure will be higher and may never drop below 25psi so it runs constantly.

It may also stay engaged at idle and cycle at higher rpm.
 

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Discussion Starter · #8 ·
An odd thing happened. The next day, after reading I may still need more freon, I went backl outside to put the other half of the can in. When I started the car, it seemed to be blowing much cooler air but when I tried to put the rest of the can in, it seemed like it didn't want to take anmore in. I heard that you can't really overcharge a 112a system like the old 134 systems. Is that true? I couldn't seem to get it to take the rest of the freon. The first day I did it, it was 85* outside. The next day was only 72*. BTW, I bought the 22oz can(the big one from AC Pro)
 

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Make sure you are using the can correctly.

Yes you can put too much refrigerant in. This will cause too much pressure and in severe cases damage the compressor.

If no more refrigerant will go in then the pressure in the can is the same as the pressure in the system. Some of it may have leaked out from your connection or a leak in the system somewhere. Or the system may actually be full and you have a problem elsewhere like a bad pressure switch or ????

Without knowing the actual pressure in the system now you are limited on your ability to accurately diagnose the problem.
 
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