_loud_ hammering sound from HP lines

[rwfisheriv]

We've got a 10yr old Lennox HP. When the unit kicks on, you can hear the blower fan spool up, and then a loud hammering/thumping noise follows and then dies out. The noise doesn't seem to be coming from the HP unit itself, but from the freon lines which vibrate and shake when this happens.

Any ideas? A bad valve somewhere?

[Ed Imeduc]

Feel the lines there at the inside coil big and small . would you say its there.. There is a check valve there and could have a TXV v alve. Also ,out side unit has a called 4 way valve that lets you have heat or cool. Sure its not the blower? Turn to just fan on and see if you get it then. Filters clean, coil clean.

ED ;)

[rwfisheriv]

We had the unit serviced about a month ago, and the tech cleaned the coils and replaced the filter then. The unit had stopped running because a clogged filter tripped a reset in the HP (we had a stairway sanded/etc and didn't think about the sawdust....oops)

Both the HP and LP lines shake, but if I had to pick I'd say the large line (LP?) was shaking more. We're getting heat out of the unit, so would that imply that the 4-way valve is working OK? I guess it could be sticking for a second or two and then releasing......

[mattison]

I would go out and listen at the outdoor unit on start-up. Kinda sounds like it could be slugging.

[rwfisheriv]

Would this be due to a valve malfunction? What's slugging?

[Ed Imeduc]

Some units have what is call a oil heater or crankcase heater. So when its cold out it will keep the freon in a gas from the oil if not it can be a liquid and when the compressor starts it can slug it. Also just serviced it ???did they put freon in ??? Could have it contaminate it or got noncondensables in it.


ED ;)

[rwfisheriv]

Well, it wasn't the lines after all...apparently the compressor was dying. Oh well...time to get an updated HVAC system....

[mooredd]

All heat pumps switch the reversing valve in the freon system when defrosting or changing modes from heating to cooling. Some reversing valves are more noisy than others. My 3.5 ton Armstrong HP is reasonably quiet. What will help is to make sure none of the refigerant tubing in the heat pump inclosure or in the house is touching metal or wood. You will find eliminating :) contact points like those mentioned will greatly reduce the momentary noise when the HP reversing valve switches position.