Recharging A/C system

I have a '66 Mustang with V-8 and factory A/C with Sanden compressor conversion using 134A refrigerant. The system was fully charged with 134A about 3 years ago and putting out very cold air. Now it is putting out cool but not cold air. Time to add more 134A refrigerant. The compressor has 2 lines coming off the back of it. One line goes through the radiator support to the condenser and has a red cap on it. The other line with a blue cap goes back from the compressor through the firewall. I'm guessing I put the new can of 134A I bought into the blue cap line and fill with the motor running and the A/C full on while I do it. The can has a pressure guage with a limit mark on it to help determine when the system is properly charged.
Any tips or do's and dont's I should know about before attempting this procedure? Thanks.  

Hi Jbirch, sorry to interrupt but I wanted to ask what would be the pros and cons of running R134A on an a/c system that previously ran R12?

I am looking into recharging my a/c system this week. the system currently has gas running in it but not enough for the A/C to cool the air so, by this, im assuming I do not have any leaks in my system.

Would I have to look into changing the hoses because of the new R134A gas? I read an article stating that it might deteriorate the hoses if it does not have the correct lining. Has anyone else seen this before?

Thanks. I will appreciate any kind of help you guys can give.  

Jbirch:
I have a '66 Mustang with V-8 and factory A/C with Sanden compressor conversion using 134A refrigerant. The system was fully charged with 134A about 3 years ago and putting out very cold air. Now it is putting out cool but not cold air. Time to add more 134A refrigerant. The compressor has 2 lines coming off the back of it. One line goes through the radiator support to the condenser and has a red cap on it. The other line with a blue cap goes back from the compressor through the firewall. I'm guessing I put the new can of 134A I bought into the blue cap line and fill with the motor running and the A/C full on while I do it. The can has a pressure guage with a limit mark on it to help determine when the system is properly charged.
Any tips or do's and dont's I should know about before attempting this procedure? Thanks.

Here's a site with the major tips.
http://www.aa1car.com/library/ac_recharging.htm  

I have gone back and forth between R12 and R134a over the years on my 1966 289 with the stock A/C unit. Here are my opinions on the pros and cons.

R134a is cheaper per pound of charge than is R12, dramatically so. You can buy R134a at your local auto parts store if you want (the same cannot be said for R12 anymore - at least not in California). With a new Sanden compressor R134a will cool just as well as the old stock system with R12.  And, R134a will not destroy the ozone layer.

That being said, I swapped back to R12 in the last 1-2 years. In fact, I just had 1.2 pounds of R12 added to the system last week to boost the low charge. (note: you cannot mix the 2 refrigerants, or at least so I am told)

R12 has a higher cooling co-efficient than does R134a (think of it as the difference between an old brass radiator and a new aluminum radiator). In the old stock A/C system I have found (at least in my experience) that the R12 produces colder air coming from the evaporator than does R134a. If you swap to a Sanden compressor I would assume that would no longer be the case.

That's my 2 cents on the subject. R12 is is still available and I have simply decided to pay the extra cost because it cools better in my opinion with an old stock system.

Lastly, remember that R12 is pumped in with some a/c oil as well to keep the seals lubricated. So, during the winter run your a/c every 3-4 weeks for a few minutes to circulate the oil and keep the seals from drying out.  

R12 + R134a = acid.  That simple.

These neat little conversion kits where you do a quick flush, add conversion caps, and charge last about 1-2 yrs, after which you are looking at a complete rebuild. This comes from mechanics I trust that were not trying to sell me anything.  R12 is a bigger molecule and will leak out of the system slower so you will have to recharge a 134a system a little more often.  If you are looking to change systems you need change all the lines, condenser, etc now, not later.

As for the original post: Car running, A/C on high and cold.  Charge on the port the can fits on (there will be a large and small fitting on the lines and the can's hose fitting will only fit one).  Charge until you get to the desired pressure and do not over charge the system.  

Hey guys,
I am trying to find out what the specs are for the ac system. What psi did you charge the system to?  

IC237:
Normal service pressures are 28-38 low side and twice ambient temperature on the high side #.  My experience has shown though, that high side pressures in the 180 -300 range , depending on outside temperature, is normal for a fully charged system.  Remember that overcharge does not improve cooling performance, it degrades it.
JBirch:
install the refrigerant to the side that goes to the evaporator (low side/blue) with the engine running @ 1500-2000 rpm for the best charge. At this speed you should see pressure in the 30's and outlet air from the ducts should be <45 degrees.
jlg