The heater broke and I diagnosed that it was the blower motor. It's a 120V single phase brushless motor and replacement cost is about $1400! I took it out and got it to run by turning it by hand while power was supplied. This led me to think it might be a centrifugal switch or starter cap. I took it apart and found that there was a burned area behind what looked like a ceramic disk capacitor or perhaps a varistor of some sort. See the image of it attached.
It shows about 14 ohms resistance at room temp. I get an "out of range" on the DMM when testing capacitance. After poking around, I'm thinking it may be a Surge Guard Thermistor by RTI. Here's the link: http://www.rtie.com/ntc/surggard.htm
Also attached is a photo from their site. The logo on the two parts looks kind of similar, but the resolution is low. Also, I can't find the same product code in their listings, though this one could be obsolete. The SG might be Surge Guard and the 421 might be 420V RMS if one were using capacitor style coding. I called RTI and couldn't get anyone on the line or to call back.
So, what do you think this thing is? The circuit has one end from a big power diode. If it's just some over voltage protection, could it be related to my start problem? How can I test it to know? I can't afford $1400 and am hoping to get anyone to help send me in the right direction.
Also, attached are two photos of the motor driver. It looks like a 6 transistor H-bridge of some sort. The three big electrolytic caps are wired in parallel. A couple of ICs including a LS7262 brushless DC motor controller (the board is fed AC at 120V so maybe there are rectifiers in there and not mosfets) and a second IC that is unmarked. The rest are diodes (a ton of them) and a bunch of resistors, three big caps and few smaller ones, a speed control pot, the motor coils and power jack. The motor is variable speed, but has no outside controls, so I'm wondering how it senses the need to speed up or slow down. Might be a thermistor? If hot, turn up fan, if cold, slow down? If that is it, I don't think that would solve my dilemma.
Any advice on what to do appreciated. I'm about stumped.
Thank you in advance!!!
Bob
It shows about 14 ohms resistance at room temp. I get an "out of range" on the DMM when testing capacitance. After poking around, I'm thinking it may be a Surge Guard Thermistor by RTI. Here's the link: http://www.rtie.com/ntc/surggard.htm
Also attached is a photo from their site. The logo on the two parts looks kind of similar, but the resolution is low. Also, I can't find the same product code in their listings, though this one could be obsolete. The SG might be Surge Guard and the 421 might be 420V RMS if one were using capacitor style coding. I called RTI and couldn't get anyone on the line or to call back.
So, what do you think this thing is? The circuit has one end from a big power diode. If it's just some over voltage protection, could it be related to my start problem? How can I test it to know? I can't afford $1400 and am hoping to get anyone to help send me in the right direction.
Also, attached are two photos of the motor driver. It looks like a 6 transistor H-bridge of some sort. The three big electrolytic caps are wired in parallel. A couple of ICs including a LS7262 brushless DC motor controller (the board is fed AC at 120V so maybe there are rectifiers in there and not mosfets) and a second IC that is unmarked. The rest are diodes (a ton of them) and a bunch of resistors, three big caps and few smaller ones, a speed control pot, the motor coils and power jack. The motor is variable speed, but has no outside controls, so I'm wondering how it senses the need to speed up or slow down. Might be a thermistor? If hot, turn up fan, if cold, slow down? If that is it, I don't think that would solve my dilemma.
Any advice on what to do appreciated. I'm about stumped.
Thank you in advance!!!
Bob
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