Dual contactor

johnjohn89

Why there are two contactor for condensing unit?

Jamie Hall

As marked -- a high and low staging. Have to see the wiring and mechanics to know exactly what it was doing.

EBEBRATT-Ed

2 speed compressor. Bristol (I think) was the only one that made them that I know of. Trane and Lennox used them don't know about anyone else.

But if it is the one I am thinking of they had 3 contactors hi speed, lo speed and a tie contactor that switched the windings around electrically. But those contactors were mechanically interlocked as well. Usually one speed would fail as there wasn't a good way to protect the windings from overload

I am assuming you only have 1 compressor in there.

If you had a name and model # you might get mor information

EdTheHeaterMan

Two stage. two contactors
Your thermostat should have Y1 and Y2 contacts to make that system operate at its best.

Looks like an American Standard

ratio

Yeah, Bristol two capacity compressor. I say two capacity because it doesn't stage up or down for the different rates—it actually turns in opposite direction! Very neat, the crankshaft has an eccentric bushing on it that, turning in one direction, allows one piston to reciprocate, but turning on the other direction it locks in a position that is coaxial with the crank & therefore the piston doesn't move.

They're very sensitive to damage from liquid slugging so be very careful with the charge.

Jamie Hall

ratio said:

Yeah, Bristol two capacity compressor. I say two capacity because it doesn't stage up or down for the different rates—it actually turns in opposite direction! Very neat, the crankshaft has an eccentric bushing on it that, turning in one direction, allows one piston to reciprocate, but turning on the other direction it locks in a position that is coaxial with the crank & therefore the piston doesn't move.

They're very sensitive to damage from liquid slugging so be very careful with the charge.

Good grief. I thought Rube Goldberg and Heath Robinson had patents on that sort of contraption...

mattmia2

Jamie Hall said:

Good grief. I thought Rube Goldberg and Heath Robinson had patents on that sort of contraption...

I'd imagine whoever designed it envisioned a modern pcb being constructed for the controls that hooked directly to the motor instead of 3 1950's era contactors point to point wired together to control it. Reversing a motor to shift functions without additional controls isn't an uncommon control strategy for all sorts of mechanical systems.

EBEBRATT-Ed

The Bristol that @ratio is talking about is one I never heard of. The one I know had a high and low speed.

The Bristol I know of was out of VA. Now there are in Dubai. So who knows.


We are all guessing anyhow. If the OP expects any help some picture model, serial # etc would be needed. Otherwise why do we bother?

johnjohn89

EBEBRATT-Ed said:

2 speed compressor. Bristol (I think) was the only one that made them that I know of. Trane and Lennox used them don't know about anyone else. But if it is the one I am thinking of they had 3 contactors hi speed, lo speed and a tie contactor that switched the windings around electrically. But those contactors were mechanically interlocked as well. Usually one speed would fail as there wasn't a good way to protect the windings from overload I am assuming you only have 1 compressor in there. If you had a name and model # you might get mor information

Thank u

johnjohn89

Thanks a lot all of you

ChrisJ

The one I have is a Copeland and just uses a solenoid to open and close bypass holes. It's a low voltage solenoid in that case.

ratio

Some (all) if the internal bypass solenoids are 24 VDC. There's a bridge rectifier moulded into the li'l rubber cap that plugs on to the terminals (although I suppose that means it's not actually 24 volts...) Guess what happens if AC is applied to it. Hint: you'll be replacing the compressor. Honestly, I can't imagine why anyone anywhere ever thought it would be a good idea to mount a DC component inside a hermetic compressor & not protect it against AC voltage.

mattmia2

ratio said:

Some (all) if the internal bypass solenoids are 24 VDC. There's a bridge rectifier moulded into the li'l rubber cap that plugs on to the terminals (although I suppose that means it's not actually 24 volts...) Guess what happens if AC is applied to it. Hint: you'll be replacing the compressor. Honestly, I can't imagine why anyone anywhere ever thought it would be a good idea to mount a DC component inside a hermetic compressor & not protect it against AC voltage.

The same people that thought putting an overload inside a hermetic compressor was a good idea.

A bridge rectifier on 24vac nominal will give 24vdc nominal minus the junction voltage. That can be very small with barrier diodes.(although those have a limited lifespan but are more efficient but wouldn't be a good choice for this application)

pedmec

why would you lose the compressor if the solenoid fails? its just an internal three way valve that normal positioning is bypassing 33% of the load. so in a failure of the solenoid you still have 67% capacity. compressor speed is not changed unlike the bristol which is a 50% capacity but in a failure is totally gone.
just asking in case i'm missing something. never stop learning

ratio

I do new installs, which means I do 1^st year warranty work. If the compressor isn't 100% healthy, they're getting a new one.

I suppose if I was doing service work, I'd offer the customer the option of running unloaded like that. Given the preponderance of oversized equipment, they might not even notice!