AC compressor does not cycle when air is on

Hi and thanks for using 2CarPros.

If it runs all the time, there are a few things to check.

First, with the engine off, see if you can turn the clutch on the compressor. It's possible the clutch overheated and is actually sticking together, As a result, the clutch never actually disengages.

The next thing I would do is exactly what you mentioned. Hook up gauges to determine pressures. We need to determine if the sensor is working to turn the system on and off. Therefore, if pressures are met with the engine running and the A/C on, use a multi-meter to see if the sensor is sending a constant signal on. I have to be honest, the sensor is usually not the problem.

If the pressures show good and the sensor is tested good, then there has to be a short to power or the system is doing its job. What can happen is this. Your low side pressure is too low which commonly is related to low Freon levels. However, you can't add Freon because it won't take it. Most commonly, that type of issue is due to a bad compressor or a dirty or plugged expansion or orifice tube.

Here are some links that may help. Take a look through them. Also, when you get the gauges, let me know what the high side pressure readings are.

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

When you get the gauges and get the readings let me know what they are and also what the outside temperature was when checked.

Take care,
Joe

Your gauge reading is too low for the system to operate properly. As a first step, you would actually need a shop to evacuate the system to see how much refrigerant is in the system and charge to the proper level. If you are low then a leak trace needs to be done to see where you are losing Freon from.

I was finally able to check the AC pressures with a gauge set. I first checked with the car off, both the low and high side gauges were right around 50. started the car and now the gauges read: almost 0 for low side and about 80 for the high side. the outside temperature was low 80's.
the compressor operation was the same as before, the clutch does not engage until I turn the air on, but once it is on, the clutch always remains engaged, it does not cycle.
it will disengage when I turn the air off.
Unfortunately I could not add Freon as the adapter I had to go between the gauge set Freon line to the disposable Freon can was leaking.

Pressure is too low to engage the clutch. You should have a shop evacuate the system and pull a vacuum to get moisture out and have it charged to the proper level and leak checked.

Just to correct this post as going to a shop is most likely not needed. These pressures are low at a static system (turned off) and with the clutch engaged. It was mentioned that the clutch comes on but does not cycle.

This means that the system is trying to obtain a certain pressure and it cannot. Again another sign that the system is not charged properly.

The first thing that needs to be done is to pull the system down into a vacuum and make sure it can hold a vacuum. If it can then you have no detectable leaks and the system is just low.

Here is a guide that will show how to do this:

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

If there are no leaks then here is a guide that will show how to add Freon.

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon

You will want to add Freon until the clutch starts to cycle. Then you want to hook the gauges back up (assuming you are just using one of those fill cans) and check the pressure until it is with in the range on the chart below based on the ambient temperature you are doing this in.

Please run through this material and let us know what you find with this and we can go from there.