Car A/C Charging

Jrboulder · 10-04-2014, 10:56 PM

So I have a 2007 VW Jetta and I just replaced the refrigerant control valve on the compressor. It uses refrigerant to control the displacement of the compressor. The r134a charge should be 525g +- 25g according to the sticker in the engine compartment.

What I've done:

Evacuated the Freon (shop did this)
replaced part
pulled a vacuum on the system with an electric pump
charged it with 2 12 oz cans

24 ounces is 680g so that means I should be 130g overcharged. I wouldn't have put this much into the system but the pressures were really low. Even after 680g the pressures were 35/150 when the lowest they should have been was 40/175. it was about 82F ambient. I don't know how the variable displacement compressor factors into this.

Some issues I can see:
Loss from can switch-out (no liquid left in cans)
Freon still in gauge hoses
Freon loss from disconnecting hoses
Cans not really 12 oz to begin with (china)
Increased system volume from oil loss (probably not much)

Should I put more in? Should I leave it alone? It works much better than it did before and I'm tempted to call it good. A/C is used year-round here.

mattdavis11 · 05:29 AM

How close to the compressor is the low side service port? How close to the evaporator is the high side service port?

I'd let some out. 35 on the low at 82 ambient is high unless the low is really close to the evaporator. You are close, as you mentioned, and could call it good, but why not get it too the point where it will freeze you out?

I have found that the MFG's system capacities do not always achieve the most optimal cooling level. Some have the vehicle requiring too much refrigerant charge and/or too much oil.

You are to the point where you need to fine tune it. Drop it just a tad, opening the high side while the compressor is engaged. Measure the vent temps. I'm not satisfied until the vent temps are in the high 20's and the compressor cycles on and off regularly.

onewhippedpuppy · 10-05-2014, 05:54 AM

I consider the pressures and charging numbers to be more of a ballpark guideline than a hard rule. A/C seems to be a bit of a black art, so I'm with Matt. Get a digital probe thermometer (meat thermometer), monitor temps and try to tweak the charge. Make sure you have it on high fan and max recirculated A/C. If you get condensation on the low side line you're getting close.