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KC87Wagoneer 06-26-2013 09:24 PM

AC charge psi
Does anyone know the recommended charge for the ac system? I charged mine to 35 psi. Blew cold for about an hour even though it was 10 psi under recomendation on the kit. I blew a hose. Old system that sat for a while so hoses don't look great. Wondering if it was just a bad hose or if I over charged the system.

super98lsc 06-27-2013 12:36 PM

Not overcharged if 30-40 on low side typically that low side pressure will also correlate to the coil temperature within a few degrees. Ideally you want to have enough charge to fill the system so the expansion of the gas is taking place in the coil not in the lines. The side you want to watch for is the high side it should over between 125-180 depending on outside temp and if you have enough airflow across the condensing coil (in front of the radiator) the more airflow the better the system will exchange heat. Part of the reason I went to an electric fan setup doing so dropped my AC temp at idle over 13 degrees at the vents. If the system is running higher head pressures than that its either overcharged or has a blockage someplace which will blow lines and ultimately the condenser and compressor. Once the system has been opened up you need to pull a vacuum on it for 30m-45m to boil out any residual moisture, and I would change the receiver dryer (chemical drying agent gets ruined when exposed to air) this keeps moisture out of the freon. Moisture is the enemy for performance and corrosion. Ideally keeping the low side as low as you can but slightly above freezing is best. Since auto air compressors turn at engine speed you want to ensure enough charge that the low side pressure cycling switch does not cut the compressor clutch out every time the engine revs or at cruising speed. Finding the balance between stable cold air minimal compressor cycling at cruise speed (RPM) and idle air temp is best. I have found that 35 on the low side works very well here in Austin in 90+ temps I blow 48 at idle and 39-40 at cruise. Eventually it gets down to 35 but usually at night after the interior has had time to cool way down.

KC87Wagoneer 06-27-2013 06:05 PM

Excellent. So it must have just been an old hose. There lies another dilemma. I can't find a replacement line. I can splice in on the low side unless you or someone else knows where to buy a replacement hose.

super98lsc 06-27-2013 10:26 PM

usually places can custom make them, also I believe vintage air has some really cool connectors that you can use to make your own hoses now vs having to get them crimped etc. Some parts stores make them also, check hydraulic shops. I checked my pressures tonight my low side is 33-38 and high with the car not moving and the electric radiator fan on high speed is hovering around 240 and it was 109 in my garage today. I would like to see that high side a bit lower likely some of that is due to the condenser coil literally losing its radiating fins from age, they are falling off the tubes.

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