A/C pressure test

[Csaviano]

Hello guys
I have a 2001 X5 BMW 4.4

I've been having problems with the a/c compressor coming on intermittently.
When it does kick in, a/c blows nice and cold.

Grabbed a set a gauges from autozone here are the following results with an outside temp of 65 degrees
Engine off
High side 130
Low side 25

Engine on ( I hooked the compressor to power source)
High side 75
Low side 59

Can anyone give me an indication of what the issue may be?

[g300d]

My AC acted up similarly and it turned out to be the compressor. The internal variable displacement system was acting up which caused the problem to be intermitent.

[deepblonde]

Originally Posted by g300d

My AC acted up similarly and it turned out to be the compressor. The internal variable displacement system was acting up which caused the problem to be intermitent.

Originally Posted by g300d

If it runs cold intermitently, there is enough refrigerant in the system for it to work.

Low reading from the high side (engine running) can indicate the compressor insnt compressing.

It's intermintent because the variable swash plate in the compressor is on the low compression setting when it should be high, thus no cooling. Sometimes it goes to the correct setting and you will get cold air.

Another check is when you lose AC cooling, go up front and check if the compressor clutch is engaged. If it is, it's probably the compressor.

What you will see is cooling is gone, compressor clutch engaged, pusher fan will be off.

Another thing, these variable displacement systems dont engage the clutch on/off to regulate temp like older systems, it adjusts the compression internally, so when the AC is on, the clutch does not disengage unless you turn AC off.

These dont have a relay, they are directly connected to the climate control computer.

Listen here to g300d! This is almost certainly causing your intermittent problem.

[David.X5]

There are lots of regulations and safety issues for handling refrigerant. I am afraid it seems you aren't aware based on this question. I am fine helping you understand what is wrong, but please don't consider this as encouragement to vent refrigerant or some other bad move.

This site has great info for beginners:

Troubleshooting with Gauges FAQ

The pressure should be equal when the engine/compressor is off. Something weird there.
The high side pressure should be much higher when running (car on and AC set to max).

[Csaviano]

Thank you David. I realized that and plan on taking it to the shop but I want to get educated prior to doing so. I called the dealership and the want $125/hr to diagnose the issue and couldn't tell me how long it would take them.

I'll look for an Indy shop...

[Csaviano]

Crazy question. Could tapping on the expansion valve do any good? Also, can someone tell me how to identify the ac relay?

[jdstrickland]

Originally Posted by Csaviano

Crazy question. Could tapping on the expansion valve do any good?

If it does,then the valve is toast.

Over time, it is common that you need to add some R134a to the system. You can give this a try at home with a can of R134a that is fed into the Low Pressure port. You only get visibility to the low pressure side, and this is generally good enough if the issue is that the system is nothing more than depleted of some of the supply. If it does not work, then you need help from a shop.

When you buy a can of R134a, you will see some with a pressure gauge on them. Buy one of these. If it works, then you are done for about $20. If ti doesn't work, then you are only out about $20.

If it works for a short time, then you have a leak that needs to be fixed. Have you ever had the system serviced before? Your car is 10 or more years old, so needing some refrigerant is not alarming. If you need more in a year or so, (or sooner) then you have a leak from a dry o-ring,or something. You could have a problem that needs shop work, but you might not. Adding in a can of refrigerant is easy and cheap and difficult to make things worse. READ THE DIRECTIONS ON THE CAN. This option is perhaps not as effective as paying for professional service, but it's inexpensive and it usually works if there is no underlying problem. You can do it without venting to the atmosphere, but you only get visibility to the low side, and high side issues will not be seen.

[David.X5]

Tapping it won't hurt (assuming you control yourself). The weird readings with the system off suggest there could be an obstruction somewhere. Any chance someone put in one of those leak-stop products? They can really gum up a system like this.

Some of those readings are low enough the low-pressure safety switch may be keeping the compressor from running. I will try to look up that pressure value for you when I am home later.

Have you confirmed the compressor clutch it is clicking on and off? The belt spins the pulley all the time, there is an electrically actuated clutch that has to be engaged to actually turn the compressor. You should be able to hear that click on and off as the compressor cycles if you are in front of the car.

[jdstrickland]

David is the AC guy, it appears. I agree with him that the pressure seems low, and this can keep the compressor from coming on. You have to engage the system, turn the AC on, then go to the front of the car and watch the compressor. The outer section turns due to the belt drive, the center section turns on and off because an electric clutch is energized and de-energized. If the pressure is low, a failsafe kicks in to prevent the clutch from turning on. The failsafe kicks in if the pressure it too high, also. Your pressure is not high.

[Csaviano]

Thanks David. I've had the car for over 4 years and during my years I never added leak stop nor had to add freon but not sure about prior years. The ac ran great up to this point.

Yes I confirmed the clutch. In fact I hooked ithe compressor straight to the power source when I added freon earlier today. And yes, I used a can from autozone with a gauge.

Not sure if this holds any value but I did notice that the aux fan didn't come on when the compressor did. The fan is brand new installed a couple of days ago.