"water hammer" in line set

Heat pump is doing this when the unit shuts off in heat. Does not do this in cool when the comp shuts off. Reversing valve energized in cool.

Customer had a dirty ass filter and that dropped the high side pressure from 350 to 250 (during heat mode) on filter change... i noticed that the unit seemed a little low on refrig since 7* SC in 50* ambient (in cool mode). Added 2lbs of R-22, got the SC to 10* (in cool mode).

Anyway, with the pressure drop the "water hammer" is less prominent. Just started doing that this season. Also found a leak at the TXV distribution tube fitting.

Does low charge cause this due to lack of column of liquid?

132 views and no one has any theories, at least?

Is this a water to air heat pump. What is the noise you hear. Is it in the refrigerant lines. Also no mention of Superheat reading.

Rheem has had this problem occasionally in high SEER pumps. Usually replacing outdoor TXV with 10% bleed type helps. Had a couple where indoor TXV was changed as well. Apparently both TXVs shut down when the compressor stops causing it. Allowing some bleed stops the noise.

What tonnage of HP?

What size line-set?

air to air heat pump, it's not literally water hammer, but it sounds like it. the liquid line bangs like water does when it "hammers". I don't know SH... lineset is 3/8 and 7/8 by about 60'. the other thing that i don't understand is that it didn't do this for the previous 10 years they have lived there, and it's only in the cool mode. i figured that was because when it should of in cool the RV de-energized and somehow cushioned the pressure release.

The reason I asked about Superheat is if the valve is overfeeding the Subcooling will be low and to increase it you would be overcharging the system. You just can't use one condition when charging a system. You said the filter was clogged and the head was high causing the problem in heating. You changed the filter and dropped the head 100 lbs - should be a done deal. How did you notice the charge was low by running the unit in cooling with a 50 degree outdoor temp-running at those pressures you indicated why did you check in cooling ????????????? and add 2 lbs of refrigerant ?? The manufacture don't give you charging specs in cooling at that outdoor temp. No outdoor temp-indoor temp-high side press-low side press-line temps-delta across the air handler. You can't use subcooling alone. You just as well should throw darts in determining the proper charge. Be careful-you can destroy a compressor with the wrong refrigerant charge !!!

if properly charged, wouldn't my subcooling be higher than normal with low ambient and IAT at normal temp?

also, i've been told to only charge a heat pump in cool mode... is it possible to charge the unit in heat without a charging chart?

I have recently run into this with a carrier heat pump. Customer called said he had a thumping noise from the evap coil cabinet. It took me 3 trips to finally hear it. The owner actually filmed the noise for me. I looked it up online(we have iPads in the field). Found out it was a check vavle in the I door TXV that was chattering. Replaced with a new one, no more hammering in the middle of the night.

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Originally Posted by wdshea

also, i've been told to only charge a heat pump in cool mode... is it possible to charge the unit in heat without a charging chart?

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At 50 degrees outside there is no load on equipment and pressures will be off in cooling mode. The proper way to charge heat pump is to recover the refrigerant and weigh in the factory charge. But i have never seen anybody do this. If it's 50 degrees outside your suction should be around 60 in heating. What ever the outside temp is add 10 to it, and that should be your suction pressure. Also while charging in heat mode you want to watch your discharge temp. The temp will keep increasing till you put to much in then it will decrease in temp.

How did you deduce that it was the indoor check valve?

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Originally Posted by wdshea

How did you deduce that it was the indoor check valve?

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To answer your question, I called a carrier tech rep for my area and left a message. While waiting for a call back, I googled the problem and got a hit first page.(I was shocked) it was another site that someone had the same problem and what the fix was. During this I got a call back from the tech, and he confirmed what I found to be the problem and the fix