Heat pump knocks

[Jamieheatpump]

Periodically, my heat pump starts knocking and sounds like a fan blade hitting on a flang. Not so. Fan running clear and moving air. Have removed cover and fan blade moving freely. But about once every two weeks it sounds like the whole thing is coming apart.

Symptoms. Small house (Casitas Approx 800 sq ft) with external heat pump. In Tucson AZ. Pump is a Rudd maybe 15 years old. In heat cycle - Knocking is consistent in frequency and volume. (Like a revolving fan blade). Knock knock. Turned system off. 30 minutes later turned on. No noise. Huh?

SWAG - replace or repair? Possible cause and cost??

Thanks

[Brian_UK]

Is there any frost or ice visible when you get this sound?

It could be the fan blade touching the ice. If so then you need to check that the defrost cycle is performing properly.

[Jamieheatpump]

Thanks Brian. Checked - No ice. Knocking coming from lower part of outside unit - and it is loud. ttfn

[icecube51]

is it a water-air pump??
could there be air in the pipes??
could there be ice or nearly ice in the pipes???
if it is refrig al around,could it be a valve that is opening and closing to soon and to fast??

just some thoughts,

Ice

Ice

[Jamieheatpump]

is it a water-air pump??
could there be air in the pipes??
could there be ice or nearly ice in the pipes???
if it is refrig al around,could it be a valve that is opening and closing to soon and to fast??

just some thoughts,

Ice

Ice

Not sure of answers. It is an external unit with lines to house (similar to an A/C unit). Approximately a 3 foot cube. Compressor or some unit below and a fan on top. When knocking was there, fan was running free and clear. No restrictions. Knocking seemed to come from below and was consistently repeated - like a blade hitting, but no visible sign of moving part. Huh? Thanks for the input.

[icecube51]

hopefully it is not the compressor that is nocking. did you check the refrig?? high and low presure ?? when the nocking ocure,do you see ice somewhere ??
what is the brands name and type of the unit.there must be a display somewhere.

Ice

[Andy AC]

Is the fan blade tight - does the nut need doing up a bit ?
Sometimes they get loose over the years and when the fan pulses in it knocks slightly.

Andy

[Jamieheatpump]

Fan blade is tight and at different speed than knocking.

[Jamieheatpump]

hopefully it is not the compressor that is nocking. did you check the refrig?? high and low presure ?? when the nocking ocure,do you see ice somewhere ??
what is the brands name and type of the unit.there must be a display somewhere.

Ice

Unit is a Rudd Achiever 9 Hig Efficiency heat pump. Probably about 5 years old. Knocking seems to occur after unit has been running for some time. If you turn the unit off, allow it to set for 15 minutes and turn it on again, Voila. No knocking. Appreciate your help.

[Jamieheatpump]

Unit is a Rudd Achiever 9 Hig Efficiency heat pump. Probably about 5 years old. Knocking seems to occur after unit has been running for some time. If you turn the unit off, allow it to set for 15 minutes and turn it on again, Voila. No knocking. Appreciate your help.

oops. Unit is a High efficiency and is about 15 years old.