Andrei, The poster who mentioned isolating the A/C compressor on your 74 Imperial by closing the service valves was thinking of Ford products that used the in-line compressor. Your Imperial does not have such a compressor and there is no way to isolate it from the rest of the A/C system. Prior to removing the compressor you MUST discharge the system, hopefully in an environmentally-responsible way. Regarding your question about refrigerant QUALITY... When I was doing work for GM several years ago I developed some service manual text for their ACR4 unit. (Air conditioning recovery and recycling and something else). This machine is hooked up to the A/C system low and high side service fittings and it sucks the refrigerant out. The refrigerant is pumped into a 50# tank under the ACR4. With recovery complete, the technician operates a valve or two to begin the recycling process. Basically, the used refrigerant (liquid form) is pumped through a big filter/desiccant element to remove impurities and moisture. Air, being non-condensable, is also isolated and vented. You may want to visit a GM dealer to have the R-12 removed from your system using this machine. As the price of R-12 skyrocketed people started introducing all kind of crazy "refrigerants" into their cars. How about propane? Or butane? Or R-22? Or whatever is in that canister I use at work. Not a good idea for many reasons. One of them is that legitimate service personnel can't tell what's in the system and bad stuff can instantly contaminate a nearly full canister of used pure R-12 refrigerant rendering it useless. So GM attached a unit to the top of the ACR4 unit that sampled recovered refrigerant before allowing it to enter the recycling tank. The sampling unit had some solenoids, lights, and high tech stuff to test the incoming refrigerant numerous ways. Bad refrigerant shut down the recovery process. The tech was then supposed to recover the contaminated stuff into a special yellow tank for disposal. Thousands of these units were sold, but i don't know how many remain in service. Maintenance costs were high and I suspect that many units were retired as R-12 systems disappeared from dealership service bays. Independents garages could buy the units, too. They were made by Kent Moore, I think. Check with an A/C specialty outfit near you. Pete in PA Date: Wed, 30 Jan 2002 15:14:40 -0500 (EST) From: Andrei Khabarov <akhabarov_imperial@xxxxxxxx> Subject: Re: IML: air conditioning pump removal Reply-To: mailing-list@xxxxxxxxxxxxxxxx Is there any way to evaluate quality of current refrigerant and decide if I need to replace it? It's R12 unfortunately. And If it's enough good I prefer not to change it.