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AC not cold but has enough gas

Diagnose AC not cold but has enough gas

If you’re a DIYer and recently recharged your car’s AC with a AC Pro or another DIY kit and you are faced with an AC not cold but has enough gas condition, here’s what you need to know.

The pressure gauge on AC Pro and other DIY kits doesn’t tell how much refrigerant is in the system. In fact, NO gauge can tell you that. Gauges only tell you pressure, not charge level. So when you fill your system and stop in the green zone on the AC Pro gauge, you think your system is properly filled. Sorry dudes, it doesn’t work that way. AC pressures NEVER equate to refrigerant volume or weight.

In fact, you can recharge until the kit gauge reads green and easily overcharge your system. On an R-134a AC system a 1-oz overcharge can reduce cooling dramatically. Overcharging is the single most common mistake DIYers make. When it comes to R-134a, more is not better.

Why no AC gauge can tell you charge

Some people slap on a gauge and try to determine refrigerant charge with the engine off. Ah, no. That’s called static pressure and it only tells you if the system is completely empty.
R-134a refrigerant boils at -15.34°F. Add 3-ounces of R-134a to your car’s AC and let the vehicle sit (not running) outside in 70°F. Once that 3-oz of refrigerant warms to 70°F the refrigerant has boiled and is now a gas. The pressure gauge will read about 70-psi. Add another pound of R-134a and let it warm to 70°F and then read the gauge. Guess what? It’ll read 70-psi. Three ounces is severely undercharged, while 1-lb 3-oz is probably the correct charge. Yet they both read the same pressure.

DIY AC recharge kits can’t tell you charge level

Even if you use a manifold gauge set that measures pressure on the high and low sides of the system, they still can’t tell you charge level. They only tell how the system is working. Even then, you must know what type of system you have (expansion valve versus orifice tube) and the ambient air temp and cabin air temp.
DIY AC recharge kits don’t have two gauges, so they only measure pressure on the suction side of the system. The kits don’t ask you to measure ambient temperature in the car’s cabin. If you don’t measure air temp in the vehicle and use a temp/pressure chart, there’s no way the kit’s gauge will be accurate.

This post explains what a manifold gauge CAN tell you about your car’s AC

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Posted on by Rick Muscoplat

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