Update on A/C system problems

[NoSpeedLimits]

Instead of bumping up the previous lengthy thread http://www.bimmer.info/forum/showthread.php?p=32840 regarding my A/C problems, I figure I would give it a fresh thread. But, before I begin with the A/C update, I want to let you know that I got my car back and she is looking sweet with the new paint job! I'll post some pics when I get a chance, and access to a digital camera.

Okay, as per your recommendation, I picked up one of those pressure gauges at wally-mart. I hooked her up to the smaller fitting (the one closer to the front of the car). This line connects to the larger diameter tube, which I cannot at this moment recall if that is the high or low pressure side. Just so you know, before I hooked up the gauge, I made a short trip with the car (about 2 miles max) and parked it for about five minutes -- I warmed her up but I didn't run the A/C system. And, without the car running, the pressure (I believe it would be the static pressure) reading was a tad under 100 psi (about 98 psi). So, what does this number tell me? I am not sure, but too me it appears that the system has pressure, but is it enough? If it is enough, should I try jumping the LP switch to see if the clutch will engage?

As always, thanks for help and time!

[winfred]

anything over about 35 psi and the lp switch will be tripped, if the ac is not turning on i would be looking at fuses and seeing if theres any power in the circuit, there should be power to the lp switch. i've had the main control box under the dash fail and kill off all three functions of the ac switch

[NoSpeedLimits]

Other than missing fuse #8, all of the fuses appear to be okay. I can attempt to check for power at the LP switch. Before I make this attempt (I hate to ask but better safe than sorry) since I am just not that familiar with A/C systems, could someone please correct me if I am wrong, the LP switch is located on top off the drier (I think that is it's name) located under the air intake box at the right front of the engine compartment???

Otherwise, what three functions of the A/C switch would you be referring too?? Do you mean On, Off, and I am not sure what the third would be???

Also, is there any other symptoms that should I be searching for that would confirm that I have problems with the main control box???

FYI. The indicator light comes on when I turn on the A/C and all the different speeds of the blower motor function properly....there is just no cold air. And everything else in the dash appears to be functioning properly.

[Tiger]

So with A/C off... you got 100 PSI... that means you do have freon in the system... and your system is holding pressure. When you turn on your A/C... is green light lit? You also must turn on the recirculator just so you don't bring outside air in.

So what happens when A/C is on? The low side has bigger pipe than the high side... and low side will feel cold whereas high side feels warm or hot.

[NoSpeedLimits]

Yep, green light is lit. The A/C just blows hot air...one day it was working, then the next it wasn't. However, I am not surprised that the A/C is not blowing cold air due to the fact that the clutch is not engaging on the compressor. Based on TimGin's post, it sounds like my lp or hp switch might be malfunctioning. Since I have pressure, I think I may attempt to jumper the lp switch to see if the clutch will engage. I just need help with figuring out which wires to jump.

I guess my confusion with the low and high side was due to the fittings being different sizes, the smaller fitting lead to the larger diameter tube. So, based on your statement, is it safe to assume that I was testing the LP side of the system?? Oh-yah, since the A/C is not working, I never thought to feel for temperature difference in the tubes.

[Mr Project]

Well, since it's not working you won't feel a temp difference. And yes, the larger-diameter tube (with the smaller-diameter fitting) is the low pressure side.

On my '91 535i, the low pressure switch is a black connector off of the switch, which is mounted to the Receiver/Dryer. I disconnected it and jumpered the vehicle side of the harness.

[AllanS]

Does the green light being lit imply pressure, or does it just mean that the button's been pressed?

I've been having a similar problem as NoSpeed so I'm following along here.

[winfred]

rear window defroster
ac compresser
recycle

Otherwise, what three functions of the A/C switch would you be referring too?? Do you mean On, Off, and I am not sure what the third would be

[Mr Project]

Does the green light being lit imply pressure, or does it just mean that the button's been pressed?

Fairly sure on my '91 that the green light comes on with button press regardless. At least that is what I recall from my recent work. I hit the button with no refrigerant in the system and the light came on even though the compressor was (obviously) not engaged.

[sbcncsu]

Does the 94 540i have the automatic dual climate control? If so, you may have a problem with the module or the RELAY... I no longer have my Bentley but will research the ETK and TIS.

It is definitely electrical, now to trace it out. Anybody have the bentley with the wiring diagram of the A/C on the 94 540? Can anyone shed some light?