Water running sound in A/C 3

[SandCounter]

Though I often deal with HVAC in an industrial setting, it is usually in spec'ing the heat transfer requirements and letting the subcontractor select and install their equipment. I have a service tech coming out to the house and I want to help point him in the right direction. My home air conditioner has recently started to make a sound similar to the sound in water pipes when someone turns on the faucet. The sound begins about 5 minutes into the cycle and ends about 5 minutes before the end of the cycle. I looked this up online but the top search results pointed me toward the evaporator catch pan drain being plugged, but I am sure that's not the case because the pan is bone dry.

My theory/concern is that my system is experiencing a slow refrigerant leak and that the lower pressure in the return line from the condenser is allowing some of the refrigerant to evaporate and the mixture of liquid and gas in the line is causing the sound and possibly eventual compressor failure.

I am led to believe this for the following reasons:
1. The sound began early summer during days when we were experiencing record highs. This makes me think a lower pressure and higher temperature is resulting in evaporation in the return line.
2. Insulation was completely shot on the return line from the condenser. Installing some make-shift insulation seemed to lessen the sound but not eliminate it.

Could this sound be due to premature evaporation of the refrigerant, because of a leak resulting in lower pressure in the closed system and becoming more noticeable in the warmer weather?

Thanks for the help!


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[IRstuff]

You can hear this over the sound of the air ducts and the compressor fan? That would have to be pretty loud, which would hardly be consistent with a "slow" leak.

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[SandCounter]

Thanks for the reply IRstuff. Yes, I can hear the sound presumably the from return line in the wall when inside the house. I cannot hear it when I'm next to the evaporator in the attic or the condenser outside because they drawn out any other noise. To be clear, I believe the noise is entrained gas (evaporated refrigerant) in the pipe rather from the very slow leak itself.

I used to count sand. Now I don't count at all.

 

[MintJulep]

I want to help point him in the right direction.

 

[SandCounter]

Ha ha, good stuff MintJulep. What's the rate if I share a beer?

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[Compositepro]

It sounds to me that it is just water condensate pouring down the drain line. The 5 minute delay also fits this picture. Condensate will not form until a few minutes after the compressor starts running and will stop soon after the compressor stops, but the fan will still run for a few minutes after that. You may want to check that the u-trap in the condensate line is working properly. It keeps air from being sucked back up the drain line as condensate flows down. You may be experiencing higher than normal condensate if humidity is entering the house though air leaks or even a water leak somewhere.

 

[SandCounter]

Thanks Compositpro, I'll pay the $85 rate and help the repairman come to your conclusion.

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[berkshire]

Remember an expansion valve will make a similar noise if your system is low on refrigerant.
B.E.

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[SandCounter]

Thank you Berkshire.

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[IRstuff]

You might actually have the opposite problem. I recall once that the expander side was freezing over because the drain line was plugged. This resulted in liquid refrigerant leaving the expander, when it's normally all gaseous. So, liquid entrained in the gas, rather than gas entrained in the liquid.

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I can do absolutely anything. I'm an expert!

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[SandCounter]

So the tech was out to the house today I showed him where I thought the sounds was coming form and he said it was the refrigerant flashing before it got to the evaporator (which it shouldn't do). He checked the drains and the pan and said there were no plugs. He did detect a couple of leaks with his leak detector so he gave the system a charge to hold me over till I can get the leaking equipment replaced.

Thanks for the help guys.

I used to count sand. Now I don't count at all.