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So, the cheapo AC system I put on the truck 16+ years ago came up a little short recently. I was driving it yesterday and it was blowing slightly cool, never cold. Compressor sounded fine and was turning on and off with the system. Belt was tight. Compressor was hot to the touch but that's always been rather normal.

I checked it with my simple low side gauge and it had almost no pressure. Sight glass shows lots of bubbles. I had about a 1/4 of a can lying around so I put that in the system and it took it all. Still bubbles, but not as bad as before. Was blowing moderately cooler. Gauges said it was right on the edge between not enough and enough.

So I let it sit overnight planning to get some R134a today and top it off. When I jump in the truck to move it out of the way, it is blowing cold as ice. Okay, so it is happy now. Why would it kind of fix itself after sitting overnight? I also wonder, if some of the coolant had leaked out, would I have lost any compressor oil too? Can I put some more in without jacking up the whole system? I got straight up R134a, totally avoided the kind with stop leak in it, I've heard too many bad stories about the stop leak crap gumming up the works. But I haven't put any more in yet, had other things to do and haven't checked the working pressure today but I assume it is happier since it is blowing so cold now.
 

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Ideally, these systems should be filled by weight of refrigerant but I've certainly had success by filling to pressures in a table versus outside air temperature. These pressure charts are available on the Internet.

I'd probably refill with a can that has a little compressor oil in it after checking the hi and low side pressures. If you can find a can that also has a little of the dye in it that is viewable with a UV light and UV goggles, I'd go for that. That's good stuff for finding leaks.

Yea, stay away from the sealant.

Rick
 
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Was your outside ambient different? Condenser cooler since the vehicle was just started? Sounds like its still low, but that also speaks to a small leak somewhere.
 
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