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06 Apr

How To Jump 3 Wire AC Pressure Switch?

In this article, we will discuss tips about how to jump 3 3-wire AC pressure switches.

You might be having problems with your AC system but can’t seem to confirm. There are common cases wherein the car AC runs well but the switch is faulty, depriving you of sufficient AC efficacy.

That is why you might want to jump 3 3-wire AC pressure switches or perform some related DIY repairs.

Symptoms of a Bad AC pressure switch

First, here are some symptoms of a failing AC Pressure Switch

1. Unable To Cool The Car

You’ve set the knob on maximum but still can’t feel the coldness you’re supposed to experience inside the car cabin – this is a clear sign of a faulty AC pressure switch.

The system will have a hard time preserving the necessary pressure to keep the AC running.

As a result, the AC system won’t be able to emit enough cold air to keep the cabin temperature conducive due to unstable pressure.

You’ll also notice the AC takes a longer time to cool the cabin or reach the right temperature. Worse scenarios include the AC not being able to cool the cabin at all.

2. Unstable AC System

It’s normal for the AC system to repeatedly make an on and off cycle.

When the sensors detect the right temperature has already been reached, the AC system will automatically put itself in idle.

Otherwise the cabin becomes colder and colder than what’s stated in the command.

When the sensor detects the temperature has subsided to a certain level, it will trigger the AC system to turn on again to fill the cabin with cool temperature, consequently reaching the desired temperature again. And the cycle repeats.

The on-off cycle is not a problem as long as the system does it in the right interval. However, if you notice a frequent or abnormally rapid on-off cycle, you can fairly conclude there’s a problem with your AC switch.

The cycle switch is probably not functioning well.

3. Compressor Is Off

Another tell-tale sign that your AC pressure switch is no longer working properly is when the compressor is not coming on.

The AC pressure switch is responsible of controlling the on and off function of the compressor.

Failure in the part of the switch has a direct effect on the AC compressor. Simply put, the AC compressor fails if the AC pressure switch also fails.

The role of the compressor is to pump the refrigerant into the entire AC system. It’s responsible of delivering the cool air you are feeling inside your car cabin. If it’s not able to do its job, your system itself won’t be able to produce cold air.

How To Jump 3 Wire AC Pressure Switch

The three wire switches is also called as pressure transducers. These are used with GM variable control compressors and displacement compressors.

It does the process by monitoring fan operation, high pressure, and low pressure, then sending the information back to the computer for it to analyze.

The fan will turn on once the pressure level attains a predetermined high side pressure.

Moreover, too high and too low pressure will shut the compressor off. The setup for fan operation differs depending on the make and model. Careless handling will fry the ECM.

Here are some tips gathered from different owners who have experienced doing it themselves.

There are also some additional important tips related to the matter at hand. Read them all and try to incorporate what you have learned into your own application.

  • RESET PCM before you do anything. You just have to pull the PCM fuse for around one minute or a little more.
  • The correct way to force the compressor clutch to pick is to jump across AC relay B1 to B4.
  • Jumping any of the three wires will keep the compressor from running as it throws an AC DTC error.
  • The three wire is not a switch – it’s a sensor that sends zero to five (0-5) volts pressure reading on the black/red to the PCM. So keep the preceding tip in mind.
  • Do not run the system without a refrigerant unless you want to burn your compressor out.
  • ALWAYS de-energize (remove power) by resetting the PCM, which will reset the AC DTC. Do this either if you will attempt to jump the sensor wires or when you attempt to jump B1 to B4. This tip is highly important because you might end up with an unresponsive compressor after you fix the initial problem.
  • In some models, you can disconnect the shorted connections and the pressure switch connector until you can hear the AC compressor clutch relay to kick in. This serves as a trick that fools the system into operating, allowing you to immediately start charging the system.
  • Once you already have enough Freon (or any refrigerant for that matter) in the system, you can now have the connector back on. Eventually you will finish charging.
  • Commonly, the black and brown wires are the ground.
  • If you are refilling Freon, it’s more advisable to have the bottle upside down. You are allowing only the gas to flow (and NOT the liquid) when you position the bottle right side up. As a result, you won’t be able to transfer enough refrigerant to kick your compressor on.
  • Open the valves to allow the gas to flow in if you connect the filling hoses to the low pressure side. The compressor will still have enough pressure to start it even if the system was fully evacuated before the beginning of the charge.
  • NEVER invert the can to permit the liquid to flow due to the absence of accumulator between the low side port and the compressor.
  • Based on their experience, some users have their compressors ruined when they introduce the liquid into the compressor’s suction side.
  • If the temperatures are reasonable and the compressor is running well, you will get 30 psi if you connect a can of R-134a into the low side. However, if the day is really hot and the compressor is not running, you will get around 70-80 psi. You just have to hope you’re living in a state where harsh conditions doesn’t usually exist because you’ll surely have a harder time handling the issue.
  • If you have an empty system, a can of R134a would suffice to give pressure sufficient to kick the pressure cutout switch on.
  • Before you try refilling, it would be better if you have vacuum pump on the system. The device helps pretty well in terms of drawing vacuum. You can expect the cutout to activate right after you crack open the valve to allow the gas in. 


The AC pressure switch indeed plays a very significant role in ensuring a comfortable environment in your car – and that is only possible if the AC system is working at optimum level.

The said pressure switch ensures a stable AC system in terms of service life and proper operation.

Preserve the integrity of your system by addressing possible symptoms that you might notice while driving your car.

First, you must know the symptoms of bad AC pressure switch so you can properly diagnose the matter at hand.

To confirm everything, you can call a professional technician and let them handle the rest. You will be told whether you need to replace your AC pressure switch or not.

You must also keep in mind some tips on how to jump 3 wire AC pressure switch for future references.

There are surely some risks that may come but handling the issue is part of being a responsible car owner. Start incorporating what you have learned right away.