Rick's Free Auto Repair Advice

Recharged Car AC still warm

Added Freon still not cold

If your car’s AC isn’t blowing cold air it might be low on refrigerant. In most cases you can recharge car AC systems yourself with a can of refrigerant, a charging hose and gauge from any auto parts store. But what if you’ve followed the directions on the can of refrigerant and your car AC is still not cold? Well, let’s take a look at the most common do it yourself mistakes, along with other possible causes.

Overcharging car AC is the most common mistake

DIYers think that adding extra refrigerant will make AC Protheir system pump out colder air. WRONG. Refrigerant R-134a isn’t very forgiving whether the system is undercharged or overcharged. In fact, if you add as little at 2-ounces beyond recommended capacity, you can decrease cooling by almost 50%.

These DIY kits attach to the low pressure line and recommend adding refrigerant until the dial gauge needle appears in the green zone. Charging a car AC system by is NEVER an accurate way to get the right charge. If done properly with a manifold gauge set, a known amount of ram air and an ambient temperature gauge, a professional technician can get close to the right charge. The technician would attach a gauge to both the high and low pressure lines, measure shop temperature, outlet temperature and temperatures going into and out of the evaporator. Using all those pressures and temperatures, a pro can calculate how the system is working and whether it has the right charge. However, the ONLY way to get an accurate charge is to evacuate the system and add refrigerant by weight.

Can you get the right charge using a DIY kit? Close, but not exact. Overcharge or undercharge and you’re going to get warm air.

Adding too much oil is the second most common mistake

Car AC systems need oil to keep the compressor lubricated.

PAG 46 oil

PAG-46 AC compressor oil

When there’s a leak in the system, oil escapes along with the refrigerant. So you have to add oil back into the system when you recharge car AC. But how much do you add? There’s the problem. You don’t know. If you add too much oil, you DECREASE cooling. That’s because the oil coats the interior walls of the evaporator and condenser and that reduces overall efficiency.

Every car maker specifies a different car AC oil viscosity. That’s another area where DIYers get into trouble. There’s no single car AC oil that works well in all cars. If you just bought a can of pressurized car AC oil, you may be screwing up the system.

Jumpering across the low pressure switch is another HUGE mistake

Most car AC recharge kits tell you to turn on the AC and double check that the compressor is spinning before adding refrigerant. But if your system is so low on Freon that the compressor won’t kick in, jumpering the low pressure switch can literally destroy your compressor. Here’s why.

Freon (refrigerant) carries car AC oil throughout the system. If your system is low on refrigerant, chances are it’s also low on oil. Once you jumper across the low pressure switch, the compressor starts pumping the remaining refrigerant through the system. But that refrigerant is low on oil. Like any mechanical device, an oil-starved compressor overheats and fails. In some cases, the failure can be so catastrophic that it throws shrapnel thought out the system. Bottom line; don’t jumper the low pressure switch.

Recharged car AC still warm

Ok, we’ve covered the things you can do wrong to cause problems. But what if you recharged properly and your car AC is blowing warm air or is working sometimes, but not others?

See these other articles for testing procedures to solve those problems

Car AC blows cold then blows warm

Recharged car AC still warm

Car AC blows cold at highway speed but warm at stop light


©, 2017 Rick Muscoplat



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