Why you should never jump a low pressure switch

Learn why jumping across an AC low-pressure switch is never a good idea.

The low-pressure cutoff switch in your car’s air conditioning system serves a crucial safety and protective function. While it might be tempting to bypass this switch to get your AC working again, doing so can lead to severe consequences. Here’s why you should never jump a low-pressure switch.

The refrigerant carries oil to the compressor

Unlike engine pistons, which have oil rings to wipe oil onto the cylinder walls, AC compressors rely on refrigerant to bring oil into the cylinder. When a car’s AC system is low on refrigerant, the remaining refrigerant can’t carry enough oil to the compressor to keep it safely lubricated. If you jump across the low-pressure cut-off switch to run the compressor, you’ll run the compressor with little to no oil, which can damage it.

In addition, if the system is low on refrigerant due to a leak, chances are high that the system also lost some oil at the same time. So there’s less refrigerant to carry the oil and less oil to carry.

However, there are some instances where you can momentarily jumper across the low pressure cut off switch

If you just want to test the clutch to see if it’s working, you can jump a low-pressure switch for a few seconds to power the clutch. But if you leave it connected too long to try and recharge the system, you risk serious and even catastrophic compressor damage. Seriously. It can damage your compressor in a way that throws shrapnel throughout your AC system. That can easily cost you well over $1,500 to repair. If you want to jump a low-pressure switch to add refrigerant to your car AC, think again. That’s not the way to do it!!! Here’s why

How to add refrigerant when the AC compressor clutch won’t engage?

When you turn off a car AC system, the pressure difference between the high and low sides equalizes after a while. How can the pressure equalize if the compressor isn’t running? Simple. The orifice tube or expansion valve continues to release liquid into the evaporator as the car heats up. That liquid changes to a gas and flows into the compressor and out whichever compressor reed valves are open at the point. There’s always an opening between the high and low sides when the compressor is off.

Fill with refrigerant until the gauge reads above 25-psi

So you can start adding refrigerant gas to the low side port if the compressor clutch won’t engage. It’ll just take a lot longer. To speed up the process, warm the refrigerant can in a bowl of warm water. That will boil the liquid and increase the pressure. Swap out the water for more warm water once it cools. Repeat this process until the gauge on your recharging kit shows a pressure above 25 psi. At that point, the low-pressure switch should allow the AC compressor to engage.

©, 2018 Rick Muscoplat