Chevy Silverado ac belt knocking

[rjlenny00]

I have an 03 silverado 5.3l v8. Ac problems. Last year, my compressor (I'm assuming) would cause my ac tensioner to knock and broke 2 belts. Assuming bad compressor, I left the belt of and dealt with the heat. This year, I tried again and put a new belt on. Knocking was gone. Freon was low and I unscrewed high side valve and it flew off. Realized I had a leak at the high side valve. I then changed the valve, orifice, and accumulator. Evacuated system with pump. System helda vacuum. Refilled freon (only one can put it in the green which according to autozone is way less than what the system should hold). Blew cold at idle. As soon as I drove off, it stopped blowing cold, only slightly cool. Clutch stays on as it should. The old orifice looked like it had metal dust on it. Could it be sensor or compressor? I have the dual manual climate controls inside. Also, my truck seems to be getting low on coolant lately. Not sure if that could be related. I don't have check engine light. Please help

[carriedi]

your ac should hold 1.76 lbs of r134a. so, I don't know how big a can the parts place gave you but usually the cans aren't that big. How did you evacuate the system? and do you gauges to see how the pressures look on both the high and low sides?

and the ac system shouldn't have anything to do with a coolant loss unless the engine is overheating from the load and cooling fan operation...

[rjlenny00]

The can was 15oz. They said system should hold 28. Maybe oil in lines and coils? Metal on orifice makes me think valve in compressor also. I'll get readings on my lunch break today and post

[rjlenny00]

Ok, just got readings. Clutch started cycling again and when clutch is running I have 85 on the low side and the high side climbs all the way to 425. When clutch kicks off, they both go to 140

[carriedi]

85 on the low side is too high. should be somewhere around 30-35 depending on the ambient temp. High side is way too high. you should take some refrigerant out. also check to see if your cooling fans are working properly. if your low side can get down to 30-35 your high side should be 150-225 also depending on ambient temp and stuff.

Having the high side go to 425 could start to damage the system. (that's why they have the high side shut off in the system but still, 425 is looking for somewhere to escape!!!)

[TerryAuto]

I have an 03 silverado 5.3l v8. Ac problems. Last year, my compressor (I'm assuming) would cause my ac tensioner to knock and broke 2 belts. Assuming bad compressor, I left the belt of and dealt with the heat. This year, I tried again and put a new belt on. Knocking was gone. Freon was low and I unscrewed high side valve and it flew off. Realized I had a leak at the high side valve. I then changed the valve, orifice, and accumulator. Evacuated system with pump. System helda vacuum. Refilled freon (only one can put it in the green which according to autozone is way less than what the system should hold). Blew cold at idle. As soon as I drove off, it stopped blowing cold, only slightly cool. Clutch stays on as it should. The old orifice looked like it had metal dust on it. Could it be sensor or compressor? I have the dual manual climate controls inside. Also, my truck seems to be getting low on coolant lately. Not sure if that could be related. I don't have check engine light. Please help

I have seen this several times. The A/C compressor is bad. It may have also damaged the belt tensioner. The belt tensioner is causing the knocking noise. It may be hitting a transmission line also.
The problem in the compressor is what is called a wave plate. This is what controls the pressures. The pressures are getting too high causing the belt to knock since the compressor is almost locking up. Replace the A/C compressor.