Do it Yourself A/C Recharging

[Lou F]

Hello I am a new member and I have a '69 280SL with the original Fridgeking under dash air conditioner.  The A/C is not blowing cold air.  There is a label on the inside of the hood that states the A/C has been converted to R134a in 2007.  The family of the previous owner mentioned that the A/C was recharged a few times.  So I am thinking about using a do-it yourself A/C recharge kits like A/C Pro.  Is there any harm in using this product since the A/C has been converted to R134a?   And has anyone had results using something like A/C Pro?
Thanks
Lou F

[w113dude]

Hi Lou,

If it has been converted that means you can use  R134a gas, just make sure there are no leaks along the way otherwise your gas will not last long.

[Lou F]

Thanks for the quick reply w113Dude,
I know there is a slow leak in the system because the previous owner (my father-in-law) had issues keeping the Freon contained.  I think I am going to take a chance and purchase the A/C Pro kit. It is about $40.00 US and it is one of the few kits with a long hose.  I was just checking if it can do more harm than good.  So I will give it a try in a week or two.
Lou F

[enochbell]

Would suggest being careful with the pressure, read the directions and do not exceed the recommended fill, otherwise you risk blowing seals.  Good luck,

g

[Lou F]

Well I decided to recharge the air condition myself with a do-it-yourself product called A/C Pro ($39.99 US), I also purchased a Thermometer to measure the ambient and A/C vent temperature.  I have taken photos to document the process because my writing skills are pathetic.  I have chosen the A/C Pro kit because it had a built-in gauge that will compensate for the ambient temperature and a long hose so the can of R134A is away from the engine bay.  You will need to wear gloves because the can will get very cold when charging, also ware safety glasses just in case.  First I weigh the can of A/C Pro because I wanted to know how much R134A the 280SL will take.  The can star weight was 945 g.  I then measured the ambient temperature at 70F and set the built-in gauge so the filled system pressure should be about 35 psig (241 KPa) when filled.  I started the car and set the Frigiking A/C to High fan and City Cooler for max cooling.  The Vent temperature was 70F.  I attached the A/C Pro hose to the low side fitting (the one with the blue cap) and checked the pressure.  It read 0 psig, so I need to refill it.  You squeeze the trigger to start filling while turning the can from 12 o’clock upright to 3 o’clock horizontal.  Then take your finger off of the trigger to measure the pressure.  I repeated this for about 8 minutes.  The final weight of the can was 674 g.  So the 280SL took 271 g or 9.55 Ounces.  After filling was complete the vent temperature dropped to 60F.  It is not freezing cold air but it will keep the cabin below 80 F on hot days.  I took the car for an hour drive and the vent temperature was 58 F the cabin stayed at 75 F when the outside temperature was over 80 F. 

[Lou F]

The photo in the previous post was the final pressure after the fill.
The two photos in this post Is the can of A/C Pro on the scale and the location of the low pressure air condition fitting for R134a.

[George Des]

The R134A works at a higher pressure than the R12 charged system. This is one of the reasons the connections on R134A systems are made on the hoses with o-ring fittings rather than compression fittings. In addition, the newer hose with R134A systems is a barrier hose that has less tendency to allow the R134A gas molecules to leak out. This becomes a non issue though with the older hoses running the R12 after a period of time where the R12 oil will effectively form a seal on the inner part of the hose. You still may have an issue though with the fittings, especially if you over pressurize. You can get a lot more cooling effect out of the R134A set up if you change out the Frigiking/Kuhlmeister stock condenser with a newer aluminum parallel flow condenser available through most A/C suppliers. With this setup you can also eliminate the small condenser mounted under the front bumper. Whenever you go from an empty charge you really should evacuate the system so as to hold a vacuum for a few hours. This ensure that there is no moisture in the system that could freeze up the expansion valve. There are venturi type evacuation tools that work with a compressor to do this, but the vacuum type pumps are much more efficient and are now not that expensive. You should be able to find one for $125-175 and will make the job much easier.