Zumkopf

I've searched the forum and read the threads and I'm more confused than ever. Every other car I've ever had, the procedure is simple: (1) hook up the vacuum pump to the high and low pressure ports; (2) evacuate the system and pull a vacuum at least 15 minutes; (3) disconnect the vacuum pump and cap the high pressure port; (4) tap a can of R134a and feed it through the low pressure port; (5) when the pressure equalizes start the car and continue feeding R134a (along with some oil) through the low pressure (suction) port. When you've fed it the capacity, stop and cap the low pressure port. Simple. And I have the equipment to do that - a manifold with high (red) and low (blue) and vacuum/feed (yellow) hoses and connectors, and a good quality vacuum pump.

But the '98 A8Q only seems to have a single port, the high pressure one at the front. Where most cars have a low pressure port, this Audi has a sensor or switch. Now I've read one poster saying you charge it through the high side only, pulling the switch connector so the compressor doesn't kick in, but it also mentions using some machine (a Kent ACR4 or something) that I'm guessing is simply a vacuum pump and the hoses in a single cabinet, but whether it is or no, that post didn't really explain how the charging through the high pressure side is done anyway. Others suggest pulling the sensor/switch and screwing on an adapter, but suggest the threading doesn't match and I'm not clear how that wouldn't simply allow the whole system to leak out when the adapter is removed to reinstall the switch.

I love the car but there is a limit as to how much one can rationally spend on a 21 year old machine that's worth maybe $1500 on a good day. I'd really appreciate it if someone could tell me (or point me) to the procedure for this, using the usual equipment.

Zumkopf
1998 A8Q (D2) 144k

jfrahm

I have a Harbor Freight vacuum pump and manifold and I can connect a charge setup to the rig and purge out all the air using the refrigerant. Then close that off, vacuum the system down, then open up the charge again and fill the system. You do not want to disconnect anything with a vacuum on the system or it'll immediately fill with (wet) air.

It might be possible to charge it up fully via the high side with the engine off, I have not tried. You might have to keep the can of refrigerant in a pan of warm water as there will not be a huge pressure differential. Seems risky as you'd have to shut off the charging valve and start the car, run the system up to pressure to see what your vent temps are like. then let it equalize again if you needed to add more gas. Unless you just charge by weight. That'd probably work, but there is loss so you'd end up over-charging a bit, then shutting down the charge rig and testing. Then drop the high side down to the appropriate pressure based on temp.

You can easily add enough gas to the high side (engine off) to get the compressor to kick in so that's not a problem.

Me, I'd get the low side port rigged up but that's how I've done AC for many years.

JAA 4.2

Take it to a shop that can fill from the high side. It cost me about $150.

Dr. A8

The low pressure port is under the driver's side cowl/cover. The fitting is not standard but you can buy an adapter that lets it work with standard A/C equipment.