how much A/C charge to put in?

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Posted by Peter ( on 16:30:27 06/10/14

2000 K1500 Sub with rear air

The sub was not putting out cold air (A/C). Last summer I had a similar problem and I put in a couple 12oz. cans of R134. At that time, I could tell it worked because the I heard the compressor kick in and the pipes got some ice on them.

This year, I added the first can (12oz.) but the compressor kept cycling on/off every 30 seconds. Pressure gauge on the fill mechanism showed pressure going from below 25 to about 75 then dropping back down again. I think, but I can't confirm, that the rise in pressure actually came when the compressor was off. Maybe I just wasn't clear on which sound indicated the compressor running. On my truck, I can't actually see the compressor from the top of the engine. Anyhow I added a second can (12 oz.) and the pressure stopped rising so high and the low end crept up a little. Now it topped out around 60 before dropping. It also stopped cylcing as quickly. I figured, as long as adding more R134 was helping bring the pressure to the proper indicated range (35-45) and stayed pretty level, I was making progress. I added a 3rd can (12 oz.) for a total of 36 oz. The pressure did not change as much on the low end but did come down to about 55 at the high end.

My question is: the label in the engine bay says 3 pound capacity for R134. I added 36 oz. so I still had another 12 oz. to go. I ran out of cans so I stopped here. Do I get another can and add it or leave it alone until it stops cooling again?

I don't mind playing this game when I am the driver, but this problem has forced me to give my son my daily driver ('11 Sonata) and I am driving this gas hog. He is away working for the summer and I didn't want to get the phone call saying the truck isn't working. I probably should have my mechanic check it for a leak with dye but it is a hassle leaving the car with him and getting rides.

Any thoughts on adding more R134 or any other suggestions?

I am thinking about lowering the reliability rating of the truck (my personal rating of how much I trust it not to be a problem). This would mean not having the kids take it to college due to things like leaky rims, leaky A/C and a tempermental dashboard HVAC control. I could get those fixed but are they the right investment? To give the entire picture, there is rust spreading from the rear wheels forward through the rocker panels but it is otherwise a solid and clean truck.

Thanks as always for your thoughts.

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