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Old 24-11-2014, 08:39   #1
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Flushing HVAC System

I have 2 HVAC systems on my Hunter 42 Passage. Both systems use a common pump to circulate water through the heat exchangers. The water running through my rear unit (Cruiseair) has slowed down considerably compared to its normal flow and compared to the flow from the front unit. I have disconnected the piping at the pump and "blown it out" using a garden hose (I get a good flow rate with the hose connected only to the rear unit). I have also tried flushing the piping using vinegar (A mild acid). These actions have removed some visible sludge and debris but the flow rate is still not normal. I have checked and replaced the circulation pump impeller, cleaned screens etc. Does anyone have suggestions as to the next step?

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Old 24-11-2014, 09:08   #2
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Re: Flushing HVAC System

Go to Lowes and buy a Gl of pool acid, also used to clean concrete, Muratic acid.
flush out the AC unit with this. Most recommend about a 25% solution. Be careful with this stuff and Google flushing marine AC with Muratic acid and you'll get a lot to read.
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Old 25-11-2014, 18:33   #3
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Re: Flushing HVAC System

Get a gallon of Rydlyme, much safer in all aspects of handling, enviroment, and safe for Hx's
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Old 06-12-2014, 13:29   #4
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Re: Flushing HVAC System

I have used Rydlyme and muratic acid and found the muratic acid to clean better but it is definitely more dangerous. Just be extremely careful. Don't use over 25% acid strength. 1/4 acid to water. I pump it through the ac units for about an hour or two using a small 500gph bilge pump in a 5 gal bucket.
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Old 06-12-2014, 16:21   #5
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Re: Flushing HVAC System

PLEASE if you decide to use muriatic (or any strong acid), when diluting add the acid to the water rather than water to the acid. Whatever bucket you are using for mixing, put the water component in first then pour in the acid and blend smoothly (wooden paint stir works well). DO NOT add the acid first and then pour the water on top - a splash due to a bit of overzealous water pouring will result in nearly pure acid being splashed back up onto the person doing the pouring.

As someone with professional experience with (industrial) heat exchangers, muriatic acid is excellent for the proposed task. Just don't treat it lightly, it's much stronger than your average household cleaner.
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Old 06-12-2014, 16:57   #6
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Re: Flushing HVAC System

Several Bromine tabs in the strainer is what I and a few friends have used successfully.
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Old 07-12-2014, 17:29   #7
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Re: Flushing HVAC System

Thanks all or the advice and suggestions. I think I will carefully try the muriatic acid as vinegar and the pressure of a garden hose has failed to remove whatever crud is causing the problem. I had not thought about circulating it with a pump - my flushes have been "once through" to date - so I will try that.

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