Hello
I work for a HVAC supply (wholesale) I have an associate in EE that I have not used for a while .I am looking to repair some motor end bells .I need to see the schematis because some parts have no #'s AND IT LOOKS LIKE IT HAS AN ACTIVE SOLID STATE COMPONENTS.Any help would be appreciated
Thank you

Hello
I work for a HVAC supply (wholesale) I have an associate in EE that I have not used for a while .I am looking to repair some motor end bells .I need to see the schematis because some parts have no #'s AND IT LOOKS LIKE IT HAS AN ACTIVE SOLID STATE COMPONENTS.Any help would be appreciated
Thank you

Best tip for you and a re-post ! More to come if I can find them

These high efficiency variable speed blower motors are maufactured by GE. They are used in many brands including Lennox, Carrier, Bryant, Payne, York and Trane.

There are two parts to the blower motor.

The two parts are the motor itself and the ECM module that is attached to the blower motor. The ECM looks like a black hubcab and it is attached, to the motor, with two long bolts.

You can remove the ECM module by simply unscrewing the two long bolts. You do not have to remove the blower motor from the mounting.

The motors in different series and brands are often the same. The difference is the ECM module. The ECM module must be matched up exactly or it will not work.

What usually fails on these high efficiency units is the ECM module. A service truck can not possibly carry all of the hundreds of ECM modules that are used in the various brands and series of brands.

However, the part that often fails in the ECM unit is part number SG379 which is a black disc about the size of a quarter in the center of the ECM.

You can look at the SG379 disk and often tell it has failed without any further checking. The disk will often be broken, brittle or disconnected from the circuit board, and there will be an obvious spot on the circuit board that has received a lot of heat. As long as the board is not broken, or deformed and the traces are in place, then this componet can be replaced. This component is designed to take a lot of heat and the circuit board will be discolored from the heat. This is normal and this is common.

This propierity part is a thermistor and it is used for surge protection as well as regulating the current to the motor.

SG379 has a finite life and like a light bulb it gets weaker and weaker until it finally just fails.

Although not available from GE or any or the HVAC companies, a SG379 part substitute, manufactured to OEM standards, is available from amazingkeys.com and can be soldered into the ECM circuit board in about 5 minutes.

If you are a serviceman, you can keep a few of these parts on your service truck and have the unit up and running in one service call and not have to replace the motor or the ECM. This also saves the customer a $1500 blower motor replacement or an ECM replacement.

More info

More stuff

BTW the schematics are proprietary information and not available unless you work for the manufacturer under normal circumstances.

The SG379 component is hard to find. I contacted RTI Electronics who manufactured the part and they indicated that SG405 was a suitable substitute with the same specs. Both are rated at 1 ohm, 30 amps. They went on to say that any inrush current limited rated 1 ohm, 30 amps would work just fine. I actually wound up ordering SL32 1R030 from Newark electronics since the others are either impossible to find or are only sold by companies that have minimum order requirements. The SL32 1R030 cost $2.36. There are ECM motor module repair kits ( VZREP) offered by Zebra Instruments but after researching the specs and calling Zebra Instruments the component is only rated at 20 amps. I did order an ECM Motor Protector (VZPRO) to help prevent future damage from voltage spikes. While I already solved my problem I spent several days sweating without A/C because the specs for the SG379 are not readily available and RTI Electronics was did not return several of my calls. I wanted to share this information to help he next person who found themselves in a similar situation. Hard to believe that a $2 part almost cost me a $1000 repair bill. Thank you internet!