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-   -   Carrier 58SXB100-LG failure (http://www.diychatroom.com/f17/carrier-58sxb100-lg-failure-16304/)

hoistdoctor 01-28-2008 05:58 PM

Carrier 58SXB100-LG failure
 
I am troubleshooting a Carrier 58SXB100-LG furnace that almost always gives a 3-1 fault when it goes off. The draft inducer ramps up, the high pressure switch makes, the pilot lights, the main valve opens and it fires, the draft inducer maintains a study speed of about 75% full, the main blower ramps up, then the inducer ramps down, the pressure switch opens and the burner goes off. Sometimes (not often) the inducer never gets up to speed enough to make the pressure switch and it faults with code 4-3. Fault 4-3 is "RPM ratio out of range" and 3-1 is "hi pressure switch fault". Tubing to pressure switches is all clear, vent and fresh air piping is clear. Anyone know what's going on? I am at a loss!

bigMikeB 01-28-2008 06:39 PM

I'm not familiar with that model number, is the draft motor variable speed? Is the discharge piping clear (no nests, etc) ? Have you put a magnehelic or manometer on the tube to the pressure switch? I would lean towards the fan motor being on its way out. Take a look at the amp draw as it starts and runs a while.

hoistdoctor 01-28-2008 08:42 PM

The draft motor is 3 phase, variable speed. The discharge piping appears to be clear, it has a screen over the outlet. I have not measured the pressure with a magnehelic. The fan motor draws 0.7 amps at rated speed (you can force top speed ) I was concerned about the motor because a here a slight squeal when it starts sometimes, but at top speed it runs smoothly.

HvacWiz 01-28-2008 09:00 PM

Check the secondary heat exchanger, sounds to me like it could possibly be plugged up.

bigMikeB 01-29-2008 05:22 PM

Quote:

Originally Posted by hoistdoctor (Post 93028)
The draft motor is 3 phase, variable speed. The discharge piping appears to be clear, it has a screen over the outlet. I have not measured the pressure with a magnehelic. The fan motor draws 0.7 amps at rated speed (you can force top speed ) I was concerned about the motor because a here a slight squeal when it starts sometimes, but at top speed it runs smoothly.

I have huge doubts that a residential furnace has a three phase draft inducer, homes don't have three phase power run to them.

hoistdoctor 01-30-2008 10:03 AM

I agree that houses do not have three phase services but the variable speed motors used in the newer furnaces and in many front load washers use VFD drives and three phase motors. I have had to repair the VFD drive for the blower motor in this furnace twice before. A VFD drive will convert the single phase to 3 phase as well as giving you practically infinite variable speed.

bigMikeB 01-30-2008 05:45 PM

I'd hate to see the price on a replacement inducer motor for that furnace. A VFD by itself won't change single phase into three phase, that is a component transformer in the VFD. Most of the variable speed furnacesI have worked on use DC motors. How old is that furnace? I couldn't find that model on Carriers site at all.

hoistdoctor 01-30-2008 06:18 PM

The owner says the furnace is about 20 years old. A VFD drive (better known as "freq" drive) easily changes single phase to three phase and is cheaper than a phase converter in small sizes. It has a converter section that rectifies the AC single phase to variable voltage DC then pulses the DC into three phase AC by an inverter. With todays technology, the prices of the VFD's have gone down. A three phase motor is always cheaper than a DC one and the speed is proportional to the applied line frequency. Unless it is very small a three phase motor is always cheaper than a single phase motor.


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