A/C pressure test

[David.X5]

Would you let the car sit for awhile (like overnight) and then measure the high and low side pressures with the engine still off and then start it, turn the AC to max and measure it again. Check to make sure your new fan is running.

Do you have a sense of how much refrigerant you added? The total capacity is on a sticker in the engine bay - I recall it as 16 oz (440 grams) total.

[upallnight]

Originally Posted by 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?

Something doesn't seems right!!!

If the ac hasn't been running for any length of time prior to connecting the gauges to the system the system should be almost at equilibrium that is the high side and low side should almost be the same.

Running with the engine on and with the compressor jumped the lowside reading is higher and the high side reading is lower. Even if the system was low on refrigerant the lowside should have been lower and the high side should have been higher. I think you need a new compressor. If you replace the compressor, you will also need to replace the drier unit

[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.

[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.

[Csaviano]

Here are the new test results. Keeps in mind the aux fan never came on
1) Engine off - high was 70 and low 69
2) engine on compressor/aux fan not on - high side was 155 and low side 32
3) engine on with compressor engaged by me - high side was 115 and low side 64
4) engine on with compressor disengaged (on its own) high side 100 and low side 69

I ran the car for a few minutes and as mentioned above. the compressor/clutch disengaged on its own and didn't come back on. I forced the compressor to come on by hooking it up straight to the battery source.

[David.X5]

what was the outside temp when you made the readings?

To g300d - are you sure the 2001's have the variable compressor? I thought that came later.

[Csaviano]

73 degrees.
Based on the vin number and realoem.com this 2001 X5 BMW was produced in 12/2000

[David.X5]

Do you have a sense how much refrigerant you added? You haven't reached the static pressure on the pressure-temperature table for 73F, which suggests just gas and no liquid refrigerant anywhere. Over filling is really bad, and the total capacity is 16 oz.

Your "engine on, compressor off" numbers make sense if it is low on refrigerant AND the compressor is really on. It's building pressure somehow.

I can't make any sense of why the pressure would drop with the compressor off. Makes me worried it is off when you think it is on. The best guess is the compressor is bad. You do need to get the fan working, no compressor will be happy without it to cool the charge.

This car should have a Denso 471-1380 compressor. Unfortunately, the symptoms leave me guessing.

It's always a good idea to replace the drier when you replace the compressor.

[Csaviano]

Great David. Thank you for your help. I will take it to a mechanic at this point. On the flip side I did learn how to use gauges and and now know more about the a/c system.

[David.X5]

List on that Denso Compressor is $450 and you can get them from Rock auto or Amazon for $200-$220. Some x5 have more expensive compressors, but this is not one of them.