printerguy, how bad is the leak? Condensers aren't cheap.
khanty, an Interdynamics retrofit/recharge kit is approx. $34.99 from Wal-Mart and slightly more at any local parts houses. Kit includes clear instructions, coolant, oil, fittings, and a guage. If there is still a problem, you are only out $35. If it fixes the problem, you saved big $$$. This kit is fine for anyone seeking cold air from the vents. You should not mis-lead people about the importance of replacing all said parts in a vehicle that is worth between $1400 and $2000. I am glad you are an EPA service agent, but try not to sound like a commercial for the A/C industry with lengthy technical terms. Remember, this is a '91 Aerostar, not a 2005 Expedition.

 

Before any feudin' starts, let me say I've done it both ways - once, as khantyranitar suggests and twice as lv2race proposes. All three systems worked fine afterwards. My research before converting the Aerostar revealed that even Ford has backed away from its previous stance regarding the necessity to completely flush the system of old oil. An ester based oil is compatible with the old oil and existing components. I would add that just dumping oil and refrigerant in the system is a hit or miss proposition. There is a balance between too much and too little of any agent - something I think khantyranitar was driving at with his expertise. I just added 4oz of oil and 3 cans of R-134a to our old Taurus and Escort GT and both systems charged right back and ran fine afterwards. It took me a long time to get the Aerostar system dialed in - mostly because I had no A/C experience and it was a steep learning curve. Unbeknownst at the time, a bad fan clutch really compounded the problems I ran into and led to an unnecessary condenser replacement. Just my 2 cents worth.

 

I did not say anything about a flush, though if you open they system, you should. I'm saying you must MUST replace the accumulator, if it is the original. The dessicant inside will remove any moisture in the system. There is almost always some trapped inside. If you take this old dessicant, and expose it to PAG oil, the moisture is released into the oil, and turns into hydrochloric acid. Also, if you have lost all pressure, or have to open the system, you must have the system evacuated. And also, if you have any R-12 in your system, it must be removed before the R-134a is used. And before you go saying you have tried this, consider that mixing refrigerants is a FEDERAL OFFENSE, and is actively enforced. You may think they can't track abuses down, but consider, sooner or later, the car will be totaled, junked, or need AC repairs in the future, and if they find mixed AC refrigerants, they can, and sometimes do report it to the EPA. It also causes damage to their equipment, especially if corrosive componds have formed in the system. Retroffit is not a simple procedure, though it is not as difficult as the car makers made it out to be in the early 90s.

However regardless of any technicallities involved, you will need to properly diagnose your system, and to do that you need a manifold guage set. You need to see the high side, and low side pressures, and compare your reading to a chart (should be included with the guage set) based upon the current air temperature about 2 inches in front of the condensor. If the high side is too low, you could have a low charge. A low reading on the low side does not always mean low charge, it can often ean you have a blockage, and adding coolant to a system based upon the low side pressure alone can damage your compressor, and may result in a hose bursting. Also, the price for that kit at Evilmart is not notably cheaper, and may contain inferior products. (A refrigerant company was recently sued for selling refrigerant that was not EPA certified pure, and may have been wholesaled to companies such as Evilmart. It was also sold overseas)

 

When the A/C is being evacuated, it usually involves applying a 30" hg vaccuum to the system for about 30 minutes. Is this enough to pull the moisture out of the dryer?

 

No, the moisture is trapped in the dryer. The moisture will be trapped in the dryer, and I think the only way to remove it is to remove the desicant and heat it to a high temperature, which you cannot do yourself. Any replacement accumulator sold today contains a dessicant that works with R-12 and R-134a. Also, you may not get a true 32" of vacuum unless you are near sea level. I think for every 1000' you need to more or less subtract 1" of vacuum (you would get about 32" at sea level.)

 

Thanks, Khanty.

I think you're right about not being able to get true 32" of vaccuum unless at sea level. But that may not matter, if your intention is to create a condition of very low pressure to encourage the accumulated water to boil out. The gauge pressure is a measurement of relative pressure, and if you're at higher elevations, it's that much easier to get zero absolute pressure. Take it to the extreme, if you can take a pot of water up to the stratosphere, it will boil away, even though the ambient temperature may be only a few kelvins.

 

Well, the main point is, that once the moisture is in the desicant, it is supposed to be more or less chemically locked in there, so that it cannot contaminate the rest of the system. If the dessicant is not compatible with the oils used in R-134a systems, then the oils react more strongly with water than the dessicant does, therefor stripping the dessicant of any moisture it contains. The reaction with the glycol based oils (PAG) results in the formation of hydrochloric acid.