A/C question - which side is the low pressure valve?

[E30 Cabrio]

I'm attempting a DIY A/C recharge and need to know which side is the low pressure side on the AC

The Bentley doesn't really help out here.

It's an 88 325i Convertible, and I think the low pressure Schrader valve is the one that runs along the top of the passenger side front fender above the wheel.

Am I right or wrong?

Thanks.

[FL318is]

I will be subscribing to this. My ac is out. Has been for 2 hot months. I jumped from the fuse box and it worked just fine. I think I have a relay issue.

[E30 Cabrio]

How do you jump the compressor?

I need to do that so it creates vacuum so I can add refrigerant.

I will be subscribing to this. My ac is out. Has been for 2 hot months. I jumped from the fuse box and it worked just fine. I think I have a relay issue.

[CorvallisBMW]

The low side port sits right in front of the passenger's side strut tower. It's easily accessible, unlike the high pressure port which is tucked in closer to the fender and harder to get to (on purpose, you shouldn't hook any recharge cans to the high side!) I've done lots of recharges before, if you have any questions just shoot me a pm.

[E30 Cabrio]

The low side port sits right in front of the passenger's side strut tower. It's easily accessible, unlike the high pressure port which is tucked in closer to the fender and harder to get to (on purpose, you shouldn't hook any recharge cans to the high side!) I've done lots of recharges before, if you have any questions just shoot me a pm.

Hi,

Thanks for responding. I figured it was the one that you mentioned.
I need to figure out a way to jump the compressor to start it as I believe the compressor will not run if the system does not contain refrigerant, in order to prevent damage to the system.

Since the compressor will not run without refrigerant, I need to get it to run to create vacuum so I can add refrigerant to the low side Schrader valve.

If you can instruct me on how to 'Jump' the compressor or low side switch to get the compressor to run, I would appreciate it.

[Jscotty]

I had a similar problem and once I got refrigerant into the system, the compressor engaged. Maybe your system is completely empty and once the compressor can detect the presence of the refigerant it will come on. But if you must know how to "jump" it, all you need to do is run a wire from a +12 power source, (like the battery terminal) and apply it to the positive terminal on the compressor. But I would get some refrigerant in there first and foremost before you did anything else.

[CorvallisBMW]

Just pull the wire conncetor off of the low pressure switch and bridge the 2 prongs. That will engage the clutch and you can add in your refrigerant.

[emi325i]

you can also apply 12V directly to the clutch. Follow the clutch wire to its connector, and wire up a !!!FUSED!!! link between that and the + terminal connector located against the firewall.

[E30 Cabrio]

Thanks, I'll give it a try tonight.

[1991 318is]

The freon can will fill the system to the point the compressor will kick in. You don't need to have the compressor running. I thought A/C systems had different size fittings so you could only connect the refill can to the low pressure side.

[CorvallisBMW]

The freon can will fill the system to the point the compressor will kick in. You don't need to have the compressor running. I thought A/C systems had different size fittings so you could only connect the refill can to the low pressure side.

Actually that me be correct, you may not have to jump the clutch. I don't remember how it worked exactly the first time I filled my system from empty. e30's have the same size port on both the high and low side, it is possible to connect to either with the refill can, so be careful.

[Jscotty]

I thought A/C systems had different size fittings so you could only connect the refill can to the low pressure side.

That's true for newer cars that are under the R-134A standard. Cars set up for R-12 have the same size and shape connection for both sides. The connection itself is similar to the end of a tire stem and the R-12 kit can screw right on either connector. The R-134 retrofit kit comes with adapters that screw on to the old R-12 fittings making it possible to only do it the right way.