clacking noise from outside unit

[Blackhawk]

I have a Carrier 3 ton heat pump that is about 12 years old. Last year, toward the end of the heating season, my outdoor unit started making a clacking sound. The clacking sound has a rhythm of about 1 clack per every second or 2 seconds. It is not quite as loud as a normal hand clap. The clacking doesn't happen everytime the unit runs. I hear it about 75% of the time when the outdoor unit cuts on. It is doing the same thing this heating season, but I haven't noticed any performance loss on how it heats my home. I don't remember hearing the clacking this summer when I ran the AC. I pulled the cover off last winter and could not see anything obvious. Anyone have any ideas about what this could be and should it be a concern other than being annoying?

[HayZee518]

just something hitting the fan, a wire or a branch.....

[Blackhawk]

I really don't think it is something that simple. I have taken a look inside with the cover off and there is nothing mechanically hitting the fan. It sounds like something inside the freon system that is causing the clacking sound. I am thinking that it is the freon expanding and contracting. This clacking is very similar to how old steam pipes sound when they are warming up, but the clacking has a perfect rhythm. Is the system's expansion valve located in the outside unit?

[HayZee518]

The expansion valve is located close by the evaporator coil or the "A" coil in your ductwork. It operates off the "superheat" of the system. The bulb that operates the expansion valve is mounted at a low point on the larger line - the suction line. The clacking noise you describe may be the valves inside the compressor. Some use valves like inside your car engine, most are spring steel. perhaps one of yours is partially broken.

[Blackhawk]

Do you think that I should get serviced? It seems to heat fine and I haven't noticed it running excessively. My power bill has been normal compared to past years.

[chaka454]

Check your contactor, that might be the one getting noisy, when the contactor is going bad it sounds kinda like shattering and it could get pretty loud

[HayZee518]

good point chaka - I completely forgot about the fan contactor. yes it is true - the contactor armature, the metal part that doesn't move, has a couple of heavy copper bars called shunts. If these loosen up it can cause the movable piece to chatter when it is opening and closing - also the circuit that runs the fan contactor may be adjusted boarderline so it opens and closes in quick succession.