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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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My blower motor keeps cutting out when the unit is closed up

Customer Question

My blower motor keeps cutting out when the unit is closed up and filter installed. If I take the filter out when the blower is starting up it ramps up just fine and I can then put the filter back in place and it will continue to run at full speed. The filter is new and clean.
Submitted: 7 years ago.
Category: HVAC
Expert:  Josh replied 7 years ago.
Hi,

So you are saying that the blower motor cuts off when you put the doors back on the furnace?

Thanks-
Josh
Customer: replied 7 years ago.
It acts like it is not getting enough air flow. If I have the door to the blower off, the filter off or both, the blower runs at full speed. If I have the doors on and the filter in place the blower starts to run but as soon as it reaches full speed it starts to slow down and speed up like it is being turned on and off repeatedly. this low air flow is causing the coils to freeze up.
Expert:  Josh replied 7 years ago.
Is this newly installed equipment?? How long have you had this problem? Is it in an attic or a closet?? Horizontal or upflow?
Customer: replied 7 years ago.
The system has been in the house since 91. I have lived here for 6 years. This is the first time I have had an issue with it. It started acting up about a week ago. The wife said the AC was not working. It is in a closet. When I first started triing to troubleshoot a week ago I noticed that the coils and refrigerent line was iced up. I turned it off for a day to let thaw. Then I noticed that the drain line was clogged. Fixed the drain line and restarted unit. This is when I noticed the issues with the fan. The unit sits upright not horizontal if this is what you are asking about horizontal or upflow. I am wondering if the blower motor is week and needs replaced but I would hate to do this if it's not the problem because they are spendy.
Expert:  Josh replied 7 years ago.
I agree, you definately want to pinpoint the problem before you go unnecessarily replacing parts. Do you have a volt meter that measures amp draws?? Have you made sure there is nothing restricting your return air vents or ducts?? Is the motor getting hot??
Customer: replied 7 years ago.
No, I do not have an amp clamp. I don't think the returns or ducts are restricted because it runs fine drawing air through these as long as I remove the air filter but I will check. I have not touched the motor right after running to see if it is hot.
Expert:  Josh replied 7 years ago.
Well, from what you are saying, whenever you put a "load" on the motor it starts to stall for some reason. Let the motor run while it is stalling for a minute and then cut it off and see if the motor is hot.
Customer: replied 7 years ago.
I agree with your assesment. Do you know if there is any kind of an adjustment on the motor control that may compensate for this? Just tested the motor and it is not getting hot.
Expert:  Josh replied 7 years ago.
Yes there are different speed adjustments you can adjust. But, I feel that wouldnt solve your problem. If it is 6 years old and has never done this and is all of the sudden doing this, I would like to find out why. Do you have a circuit board in the bottom of this unit??
Customer: replied 7 years ago.
Yes, there is a circuit board right in front of the blower. Just to clearify the unit has been in the house since 91 but I have lived here for 6 years. So the unit is much older.
Expert:  Josh replied 7 years ago.
my bad, what color wire is on the cool spade on the board?? there should be spades that say cool, heat, EAC, spare or park, etc...
Customer: replied 7 years ago.
Not seeing spades that are indicated by cool, heat, EAC. I see some that look like they go to the thermostat labeled R, Y, W, G, C. Looks like they are labeled for the wire color. I see what look like pots for Blower and A/C, a set of dip switches and lots of caps, resistors and chips.
Expert:  Josh replied 7 years ago.
what brand of unit is it and how many wires are coming off of the blower motor??
Customer: replied 7 years ago.
It is a carrier. There is a plug on the blower motor with a black wire and a white wire. There is another plug with 5 wires blue, red, yellow, orange and purple.
Expert:  Josh replied 7 years ago.
ok, where does the black wire coming from the motor hook up on the board?
Customer: replied 7 years ago.
It goes to a black plastic connector and then out of it to a coil on the back of the board.
Expert:  Josh replied 7 years ago.
what other wires are on that coil??
Customer: replied 7 years ago.
The white wire that comes out of the blower motor and then 2 brown wires come out of the coil and go into the circuit board to a position labeled 24VAC SEC1 and SEC2.
Expert:  Josh replied 7 years ago.
ok, that is a transformer you are talking about.where do the other wires that are purple, red, etc.. go?
Customer: replied 7 years ago.
There is a conector on the board labeled P2 Blower. They enter the board here.
Expert:  Josh replied 7 years ago.
all of them go to a plug or what??
Customer: replied 7 years ago.
yes they all go to the above mentioned plug P2 Blower on the board.
Expert:  Josh replied 7 years ago.
what we need to do is get the blower motor running without the use of the circuit board and see if it does the same thing. To run on high speed, we need the black wire and the white wire. can you take the black and white wires and tie them in to the 120v line voltage coming in to the unit or do you not feel comfprtable doing that?? You have to make sure you get the right wires and do you know where the line voltage comes in to the unit??
Customer: replied 7 years ago.
OK. I am working on this.
Customer: replied 7 years ago.
ok I tied the black and white line voltage to the black and white going into the motor and nothing happened. Measured line voltage at 120.
Expert:  Josh replied 7 years ago.
the motor wouldnt come on??
Customer: replied 7 years ago.
yes the motor would not come on.
Customer: replied 7 years ago.
Relist: I still need help.

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