A/C contactor question

[dras]

I am going to be replacing the main AC contactors in my home heat pump unit along with the one in my parents' unit due to pitted contacts. My parents' unit has a single pole contactor in it. Is there some good reason to replace a single pole contactor with another single pole, or can I use a double pole in it's place. I would think it would be better to use the double pole to break both sides of the circuit. Along the same lines, mine has a 2 pole contactor now, is there any reason it could not be replaced with a 3 pole contactor, and just use 2 of the poles? I've seen 3 pole contactors that are actually less expensive than the 2 pole of the same amperage rating, coil voltage, etc.

Thanks,
D.

[HayZee518]

if you have the room and you know what you're doing, go for it! Just be mindful of the control voltage - 120 or 24 volts. It is normal for the contacts to get pitted. First of all they are a hard copper with a silver plating on them. Really, unless the mating surfaces are pratically burned off, I wouldn't replace them. About the only reason I would replace them if they are welded shut, in which case prying them apart would destroy them or iif the control coil is burnt up and the contact's armature is frozen in the coil support.

[dras]

Thanks HayZee -

Yes, I'm aware of the coil voltages. These are both 24V types. I just couldn't think of a reason why they would not want to have both sides of the circuit broken. Seems like it would be better than just one side, but I don't know what the design engineers had in mind when they put in the single pole. Swapping them out is not difficult, so I don't mind doing it. Neither one of these is totally shot, but I would think they would degrade more rapidly as the pitting worsens. I was only thinking of the possibility of them welding shut one day and wrecking an expensive compressor. They seem like cheap insurance in that regard.

I'm also wondering if it would be OK to upsize them. If I can get a 40/50A instead of the current 30/40A contactor for the same cost or less, does it make sense to go ahead and go up a size? It would not make sense, of course, to go down in size, but I don't see any reason not to go up.

Thanks again, this is a great forum!
Dave

[HayZee518]

Perhaps from an engineering standpoint, they put in a contactor close to the total amperage draw on that part of the circuit. An oversized contactor is just overkill, and physical size may be prohibitive, but if that's what you want or desire like I said before - go for it!. Because of a larger sized contactor, the inrush to the coil may be larger also. Make sure your control circuit can handle the additional current, or you may be blowing control fuses.