A/C boost

[X5chemist]

The X5 was taking a few minutes to blow cold A/C. Even with the auxiliary fan turning as soon the A/C button was pushed. It would get cold as soon as it started moving too. Today, i take out my A/C hoses and check pressure readings. The readings were not bad. I gave it a little boost. The system sucked in a decent amount in a few seconds. Cold air comes out within seconds of turning on. High pressure is maxed out for outside temp at the time. The previous owner had A/C work done. The compressor looks new. Other parts look new too. With temps about to reach the 100's, the system should work nice and cold. The new brushless auxiliary fan and clutch are working good.

[Purplecty]

It's nice to have good friends with fancy tools. My X5 also needed AC service when I purchased her...

[Overboost]

Originally Posted by X5chemist

The X5 was taking a few minutes to blow cold A/C. Even with the auxiliary fan turning as soon the A/C button was pushed. It would get cold as soon as it started moving too. Today, i take out my A/C hoses and check pressure readings. The readings were not bad. I gave it a little boost. The system sucked in a decent amount in a few seconds. Cold air comes out within seconds of turning on. High pressure is maxed out for outside temp at the time. The previous owner had A/C work done. The compressor looks new. Other parts look new too. With temps about to reach the 100's, the system should work nice and cold. The new brushless auxiliary fan and clutch are working good.

275 psi looks real high on the high side. I thought that should be 175 psi

Mine sits at 35 low and 175 high

[andrewwynn]

The high and low are affected by ambient.

I almost exclusively work on AC when it's "Africa hot out" and on my e53 with not variable compressor, I typically see about 45/250 at 90f=32c ambient. I wouldn't go much higher, there are diminishing returns it will actually cool less well when too much charge.

250/45=5.556
275/50=5.5

The difference between high and low is directly related to how much heat can be transferred.

(It's why it works better when low on freon but will freeze up the evaporator).

175/35=5
230/30=7.667

5.5 works fantastic without freezing the evaporator, 6.5 will freeze there evaporator for sure.

5.0 likely a little weak

The numbers both go up when ambient is higher; it's likely that the ratio almost cancels out the ambient temperature and you could charge using the ratio no matter the temp.

[X5chemist]

Originally Posted by Overboost

275 psi looks real high on the high side. I thought that should be 175 psi
Mine sits at 35 low and 175 high

Wow, that's low. Unless ambient temp is 70 degrees or so. It like to do service between 85-95 F. My non variable compressor vehicles blow A/C at 42 F! I do my own A/C work. I can get my '00 Ram to 39-40 F on a good warm day going down the road.

The X5 had good low pressure. It was close to 48 PSI. It sucked in R134 really fast. I had to turn off the valve quickly. It used less than 1/4 can. It was enough to start blowing cold air within seconds of starting up. It was taking a few minutes to blow cold unless you took off driving down the street ASAP. It was 90 degrees so low side 45-55 PSI low - 250-270 PSI high side is max range for R134. As pressure increased, fan speed also increased. Another 5 F degrees ambient temp would add another 5 PSI to low side and 25 PSI range to the high side.

What pressure really tells you is system work conditions. Good suction, good pressure, and overall condition.

[X5chemist]

Looking over parts to familiar myself more with the X5 system, I noticed the pressure switch. It doesn't seem to have a valve stem to push on does it? Does BMW require system evacuation to replace it? If so, it's the first for me. I've replaced leaking switches by unscrewing them and screwing on a new one.

[andrewwynn]

My understanding is yes on evacuate also that it's a sensor not switch so you can't simply short it out if failed to trick the system. You could prob use the right resistor though.

Not wanting to evacuate 5 cans of 134 I just put into a suburban when I discovered the pressure switch failed open that car now has a paperclip for a sensor. (with the strong warning to check the freon level periodically as to not run dry).

[X5chemist]

What year is the suburban? The low pressure switch on GM models is replaceable. If it's on the drier. I've replaced a few leaking switches. The rear A/C option ones are a PIA to work on.

Which sensor controls auxiliary fan functions? A BMW sensor is different from switches I've done on most domestic vehicles.

[andrewwynn]

Don't remember the year of suburban. It was about five years ago but it was still holding last one checked in with the owner.

The DME controls the aux fan on the X5 with input from a handful of sensors

[80stech]

@overboost 35 is perfect and 175 is just fine for a warm day.