Low blower voltage?

[cranejc]

I have a 1987 Trane Executive High Efficiency furnace, model number BLD135F960B2. The blower was not starting occasionally causing a heat overload switch to shut the furnace off.. we called in the repair guy and he said my blower motor might have a bad winding keeping the fan from spinning up, and it was really struggling to get up to speed. So I swapped the blower motor out (and cleaned the squirrel cage, and changed the capacitor). It's a 4 speed fan, but only using the hi and lo.

So I try the new motor and it seems like it's struggling too (and I think failed to start once late at night). So I did some voltage readings. In the thermostat fan "On" mode I get 120 V to the hi speed side of the motor. But in the "Auto" position I only get 66 V to the low speed. Is this normal? Also, there's a solenoid with a microswitch that closes a switch between a hot lead, and the low side of the blower. The switch is usually open and 66 V gets to the motor, but when I manually operate the solenoid, 120 V goes to the blower motor.. However, in normal operation the solenoid doesn't retract, to close the switch, to give 120 (as far as I've seen..)..

There's also a 24V transformer in there to run the thermostat I guess.. Looks like it also operaties the solenoid. Since the thermostat works, I assume the transformer is working.. but I haven't seen it work the solenoid.. where does the signal come from to give the juice from the transformer to operate the solenoid?

Kinda rambling, any help will be appreciated.

John

[beenthere]

Questions and discussions pertaining to HVAC for the home. No pricing, no DIY, Thank You.

Please read Site Rules (http://hvac-talk.com/vbb/showthread.php?threadid=1241) Thank you.

You need a tech to recheck the system.

[cranejc]

HVAC guy is coming out on Wed.. I'm just one of those need to know people.. can you just tell me if it's normal for only 66V to be going to the low speed side of the motor? If that's normal then it will save him a return trip (which he isn't getting paid for anyway since his original diagnosis was incorrect).

[Gunnery Sergeant Hartman]

The tech diagnoses your problem. You can't fix it correctly. Now you want him to fix your mess for free?

That old POS needs retired anyway. Nice guy to put your family at risk by playng with th efurnace you know nothing about...

[the dangling wrangler]

HVAC guy is coming out on Wed.. I'm just one of those need to know people.. can you just tell me if it's normal for only 66V to be going to the low speed side of the motor? If that's normal then it will save him a return trip (which he isn't getting paid for anyway since his original diagnosis was incorrect).

Have you made him aware that he won't be getting paid? Or ya gonna wait until he gets there, then tell him?

[ucsac]

Please do not give DIY help here, please read the rules!

[HeyBob]

UCSAC,

We do not give out technical advice in the open forums!

[Airmechanical]

I have a 1987 Trane furnace The blower was not starting occasionally
a 22 year old furnace is "possibly" spewwing carbon monoxide in your house

we called the repair guy and he said my blower motor might have a bad winding keeping the fan from spinning up
was this free information, is this why you got a "might" for an answer

So I swapped the blower motor out
so you spent money on a motor that "might" be bad

So I try the new motor and it seems like it's struggling too
i "guess" the motor was not bad = you waisted money on that decision

So I did some voltage readings.
but, you don't seem to know what to do with these readings

Also, there's a solenoid with a microswitch
"little hint" solenoids don't have microswitches

There's also a 24V transformer in there to run the thermostat I guess.
you guess?

where does the signal come from to give the juice from the transformer to operate the solenoid?
we know/hope you don't intend on hurting anybody, but your risking yours and your families well being

Kinda rambling, any help will be appreciated.
it's not the rambling, it's the inability to understand the damage you can do


if you decide to fix that dinosaur, you should check your house for carbon monoxide, and i don't mean with a cheap $50 home depot carbon monoxide detector



.

[bmathews]

It's 22 years old. Why even bother dumping any money into it or spending more than 10 minutes looking at it. Two words "MONEY PIT"

[WhoIsThat?]

It's 22 years old. Why even bother dumping any money into it or spending more than 10 minutes looking at it. Two words "MONEY PIT"
2/3rds of HVAC equip. this old has been replaced by now for any number of reasons.
If you fix it you have a 50-50 chance of getting to 38 yrs.