[jrpsimivalley]

went to call yesterday old trane ac only condensing unit (split system) compressor had 2 caps wired together ( one 15 and one 35) but the 35 had a small resistor between c and herm and when i tested them together got 55 instead of 50???????????????

 

[doc havoc]

Did the caps have a +/- variance (10%)? If so, you're within the +10%.

 

[Six]

The small resistor is jsut a discharge resistor and if your testing that cap and u get 35 ohms it means its good.

 

[jrpsimivalley]

guess i should have said the call was not about the cap, the outdoor fan motor was bad, just asking about the resistor for my own knowledge. if it is a bleed resistor why dont all caps have them?

 

[t527ed]

that resistor is part of the GE-Trane design using trickle voltage through compressor windings as crankcase heater.

 

[Six]

HUH ??? Been doing this 20 years and Ive never heard of that. Why wouldnt Trane just install a crank case eater ?

Im calling BS on that. Its either a start cap spplied with the unit or a hard start kit. ALL start caps have them.


Why ? Potential relay removes start cap from the circuit and the bleed resistor discharges it

 

[Six]

Start caps have to bleed out in quicker than it woul.d take them without the resistor. I think it has something to do arcing or minimizing arcing. Ill have to look it up.

 

[rundawg]

HUH ??? Been doing this 20 years and Ive never heard of that. Im calling BS on that.

If you send me an email (email is in my profile) I'll send you a document from Copeland, proving what "t527ed" is saying, is correct.

Then you can come back on here and say " I learn something new every day......."

I can't post documents in this "OPEN" Forum.

 

[second opinion]

HUH ??? Been doing this 20 years and Ive never heard of that. Why wouldnt Trane just install a crank case eater ?

Im calling BS on that. Its either a start cap spplied with the unit or a hard start kit. ALL start caps have them.


Why ? Potential relay removes start cap from the circuit and the bleed resistor discharges it

It is not BS the resister is part of the trickle system when on the run capacitor.

When it is on the start capacitor it is to discharge the cap to protect the contacts from arcing and welding together.

 

[idratherbsailing]

that resistor is part of the GE-Trane design using trickle voltage through compressor windings as crankcase heater.

Ditto

 

[Six]

If you send me an email (email is in my profile) I'll send you a document from Copeland, proving what "t527ed" is saying, is correct.

Then you can come back on here and say " I learn something new every day......."

I can't post documents in this "OPEN" Forum.

I hear you. Ill say it now " I learn something new here everyday "

Sure seems like a round about way of providing crank case heat. Ive seen that type of application on industrial motors through VFDs but never on a compressor.

My apologize to "t527ed"

 

[mgenius33]

went to call yesterday old trane ac only condensing unit (split system) compressor had 2 caps wired together ( one 15 and one 35) but the 35 had a small resistor between c and herm and when i tested them together got 55 instead of 50???????????????

You're reading 55 because you're adding the resistor to the capacitive reactance that the meter calculates to capacitance. If you removed the bleed resistor, you would read the sum of both capacitors in parallel.
That's why you need to remove the resistor to the start cap, or you'll get a high reading.
Resistors are installed to bleed the energy stored in the capacitor. Other run caps don't need one because they can bleed the energy into the windings of the motor. The configuration of the trickle capacitor circuit does not allow for this to occur. So, the resistor is installed to help reduce the risk of shock to the technician. On a start cap is also helps to reduce potential relay contacts from welding.

 

[mark beiser]

The resistor isn't there for the trickle current, it is there to protect technicians working on the unit.
"Normally" run capacitors will discharge through the motor windings in the off cycle, but with the trickle current setup, the capacitor doesn't discharge through the windings when the power is shut off to the unit, so a bleed resistor is installed.

 

[Six]

The resistor isn't there for the trickle current, it is there to protect technicians working on the unit.
"Normally" run capacitors will discharge through the motor windings in the off cycle, but with the trickle current setup, the capacitor doesn't discharge through the windings when the power is shut off to the unit, so a bleed resistor is installed.

They're saying it trickles current through the compressor windings and act as a crank case heater.

Some GE/Trane proprietary design Ive never run across. Initially I called BS but after 3 different techs said that type of CCH heater exist I changed my mind.

Ive seen open drive process chiller with large motors run current through the windings and other industrial motors that get DC pumped through the windings from a VFD before but never a compressor.

 

[Milk man]

Carrier uses a 1.5 pole contactor and a CCH. If you replace the 1.5 pole with a 2 pole and not change the wiring configuration you disable the CCH.

 

[mark beiser]

They're saying it trickles current through the compressor windings and act as a crank case heater.

Yes, I'm aware of that, I have worked on a great many systems that use trickle current CCH.
I'm just pointing out that the resistor is not part of the trickle current function, it is just there for safety to discharge the capacitor when the power is turned off to the unit, like when a technician needs to work on it.

Carrier uses a 1.5 pole contactor and a CCH. If you replace the 1.5 pole with a 2 pole and not change the wiring configuration you disable the CCH.

Yeah, a number of manufacturers have done that over the years, York used to be the most common ones to do it.