This is the Carrier part that is called for, (P291-3554RS dual cap ) The unit failed sometime in the past and was replaced with a single starting capacitor. This is causing a high enough start current to sometimes blow the 30 amp fuses. I am replacing this single capicator with the dual cap called for but I don't have a wiring diagram telling me which wire is which.. Is there a wiring diagram available for the 38ycc036300?
Are you talking about a start capacitor or a run capacitor?
Usually a dual capacitor is a metal can type capacitor with 3 terminals.
C - which is run for compressor and fan.
Herm - is start for the compressor.
Fan - is start for fan.
A start capacitor is a black plastic capacitor
It is in series in the run wire to the potential relay, one side goes to run on the run capacitor and the other side goes to #1 on start or potential relay.
You should use the correct capacitor for your compressor, because that is what phases it. That capacitor will allow the compressor to run at its most effecient level. With the 50 mfd capacitor you are probably running higher watts.
As far as running 2 of 3 phases that shouldn't effect the compressor. You might check to see what voltage you are getting at the compressor when it's starting, you may be getting a lot of voltage drop.
How is your start capacitor wired do you have a start relay or 2 wire universal start capacitor? the 2 wire isn't a high starting torque.
Hard Start Capacitor
A hard start capacitor its only purpose is to add additional starting torque when the compressor is starting for just a few milliseconds.
It is wired thru a normally closed set of points in a potential relay and in parallel with the run capacitor, when the compressor reaches a certain speed it generates enough back EMF (voltage) to energize the potential relay coil and open the normally closed set of points and then will stay open as long as the compressor is running. The hard start capacitor is only in the circuit or working for a few milliseconds, it’s not doing anything once the compressor s back EMF opens the potential relay coil.
These potential relays have different cut in and cut out voltages, so the same relay won’t work with any compressor and may actually burn the compressor up or shorten its life. The compressor manufacturer and the local parts store list the correct capacitor, start relay and start capacitor for every compressor and now they are putting the information on the compressor on the nameplate with the model and serial number.
As a rule of thumb you should be able to use a capacitor within 10% of its rating if you can’t get the correct one but you will probably run slightly higher watts.
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The dual capacitor has herm/fan/c connections. I think the problem is that the building has a 3 phase power box and breaker. The AC/Heat pump is a single phase compressor unit using only L1 and L2 input power. I'm guessing because only two of the three phases are used, the startup torque is not high enough because of the 120 degree between phases instead of the 180 degree phase difference between the single phase motor leads. I put a larger capaciter in the unit, 50uf vs 35uf to increase the lead/lag time between the current and voltage. So far this seems to be working. We'll see over time, up till now, we were blowing one of the phase fuses ever other evening. The installer used a hard start cap/? in parallel with the herm cap terminals of the dual cap. but it obviously overheated and was covered with oil. I replaced the hard start cap/? accross the herm/C terminals as well. I have no idea what the hard start cap/? does. The advertisements say it increases startup torque by 40% or so. The compressor runs quieter now. It was making a hard knocking sound before now the knocking sound is much quieter. perhaps I need even more capacitance? I went from a 35uf to 50uf. Does anybody agree with this?
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