Air Conditioning - Compressor Fan Motor Overheating
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rnelson
08-25-07, 06:20 PM
Frustrated to the max! Ok I'll try to make this as short as possible.
Lennox unit 19 years old. 3 phase all in one unit roof mounted
The fan motor on top of the condesor keeps overheating, then of course it stops running and trips the overpressure switch and everything turns off.
I have had a tech come out and look at it atleast 10 times. He replaced the contactor, charged up the system with freon, and changed the motor and fan blade out on the compressor fan.
Currently the only way he could get it to run is to reverse the motor and invert the fan blade. When this is done the motor will not over heat. But my efficency is way down. I live in Phoenix and I need this thing working ASAP.
I am going to go to home depot right now and buy a new fuse box/panal 3 phase going into the system because it is cracked. It runs with it this way but sometimes it will just shut off so I'm going to replace it so this isn't an issue.
The tech replaced the old 208-230V 1/4 HP 2.0A motor with a 208-230V 1/3 HP 2.2A motor then to try to make it not over heat he shortened the blades, but it still overheats. When looking at the motors the only differences are one the HP and the Amps. When the new motor is working the amps stay constant at 2.2A. Should we check to see what the voltage is?
Lennox unit 19 years old. 3 phase all in one unit roof mounted
The fan motor on top of the condesor keeps overheating, then of course it stops running and trips the overpressure switch and everything turns off.
I have had a tech come out and look at it atleast 10 times. He replaced the contactor, charged up the system with freon, and changed the motor and fan blade out on the compressor fan.
Currently the only way he could get it to run is to reverse the motor and invert the fan blade. When this is done the motor will not over heat. But my efficency is way down. I live in Phoenix and I need this thing working ASAP.
I am going to go to home depot right now and buy a new fuse box/panal 3 phase going into the system because it is cracked. It runs with it this way but sometimes it will just shut off so I'm going to replace it so this isn't an issue.
The tech replaced the old 208-230V 1/4 HP 2.0A motor with a 208-230V 1/3 HP 2.2A motor then to try to make it not over heat he shortened the blades, but it still overheats. When looking at the motors the only differences are one the HP and the Amps. When the new motor is working the amps stay constant at 2.2A. Should we check to see what the voltage is?
Jay11J
08-26-07, 11:23 AM
Is the motor going on 3 phase or single phase 220volts?
I haven't done enough 3 phase roof top, to know what the motor use.
My only thoughts is the the wrong motor for the phase system? Guess I can't help you anymore...
Maybe others on here can help when the sign on to see the board.
I haven't done enough 3 phase roof top, to know what the motor use.
My only thoughts is the the wrong motor for the phase system? Guess I can't help you anymore...
Maybe others on here can help when the sign on to see the board.
ecman51`
08-26-07, 12:50 PM
Does the fan run constantly? That may be key to the issue. I have seen commercial rooftop units, (unlike residential) where the fan wiring is hooked to pressure switch? and the fan only intermittently comes on. This whole process needs to be thoroughly understood by a pro.
rnelson
08-27-07, 10:48 AM
Hi Thanks for your replies.
No, the motor is a single phase motor.
As far as the pressure switch thing, I'm pretty sure that is not the case because it would shut off and then a couple of minutes later then the pressure switch would kick off of the compressor. However, now that I think of it I did one time witness it kick off and then back on for some reason. I do have all of the schematics at home so I guess I could try to see if it is wired up to a pressure switch.
Any more ideas???
I do have pics of both the old and new motors, how can I post them? do I have to use something like Photobucket?
No, the motor is a single phase motor.
As far as the pressure switch thing, I'm pretty sure that is not the case because it would shut off and then a couple of minutes later then the pressure switch would kick off of the compressor. However, now that I think of it I did one time witness it kick off and then back on for some reason. I do have all of the schematics at home so I guess I could try to see if it is wired up to a pressure switch.
Any more ideas???
I do have pics of both the old and new motors, how can I post them? do I have to use something like Photobucket?
Ed Imeduc
08-27-07, 11:53 AM
No, the motor is a single phase motor.
I take it that the unit is a single phase and not 3 phase then.
The tech replaced the old 208-230V 1/4 HP 2.0A motor with a 208-230V 1/3 HP 2.2A motor then to try to make it not over heat he shortened the blades, but it still overheats. When looking at the motors the only differences are one the HP and the Amps.
For sure get a new fan blade on that unit . The same as the old one was .
Are you sure that the RPM and it turns the same way CW or CCW are the same as the old motor. Did you also get a new capacitor with the new motor?
I take it that the unit is a single phase and not 3 phase then.
The tech replaced the old 208-230V 1/4 HP 2.0A motor with a 208-230V 1/3 HP 2.2A motor then to try to make it not over heat he shortened the blades, but it still overheats. When looking at the motors the only differences are one the HP and the Amps.
For sure get a new fan blade on that unit . The same as the old one was .
Are you sure that the RPM and it turns the same way CW or CCW are the same as the old motor. Did you also get a new capacitor with the new motor?
jim-connor
08-27-07, 01:29 PM
Are the coils clean? Reduced air flow through the condenser coil equals hotter air over the motor. Also check the items Ed mentioned.
The fan blade requires a certain HP at a certain RPM. If the HP requirement is higher than the motor can deliver, it will overheat for sure. It's OK to use a higher horse motor than the blade requires. If the new motor runs at a higher RPM, you will need more Horsepower to run that fan blade. Check the rpm's of both motors.
A wrong capacitor will cause the motor to overheat. Since it's a single phase motor, it will have a capacitor. Also, measure the voltage at the motor connections. Do you get the nameplate voltage required?
The fan blade requires a certain HP at a certain RPM. If the HP requirement is higher than the motor can deliver, it will overheat for sure. It's OK to use a higher horse motor than the blade requires. If the new motor runs at a higher RPM, you will need more Horsepower to run that fan blade. Check the rpm's of both motors.
A wrong capacitor will cause the motor to overheat. Since it's a single phase motor, it will have a capacitor. Also, measure the voltage at the motor connections. Do you get the nameplate voltage required?
daddyjohn
08-28-07, 08:21 AM
Hi Thanks for your replies.
No, the motor is a single phase motor.
As far as the pressure switch thing, I'm pretty sure that is not the case because it would shut off and then a couple of minutes later then the pressure switch would kick off of the compressor. However, now that I think of it I did one time witness it kick off and then back on for some reason. I do have all of the schematics at home so I guess I could try to see if it is wired up to a pressure switch.
Any more ideas???
I do have pics of both the old and new motors, how can I post them? do I have to use something like Photobucket?
yeppers clarify the speed of each motor and also clarify the capacitor for the new motor..If he did something to the fan blades because the new motor was overheating, my money says the new motor has a higher rpm than the old one. You're probably going to have to replace the fan blade if he cut or bent it.
he
No, the motor is a single phase motor.
As far as the pressure switch thing, I'm pretty sure that is not the case because it would shut off and then a couple of minutes later then the pressure switch would kick off of the compressor. However, now that I think of it I did one time witness it kick off and then back on for some reason. I do have all of the schematics at home so I guess I could try to see if it is wired up to a pressure switch.
Any more ideas???
I do have pics of both the old and new motors, how can I post them? do I have to use something like Photobucket?
yeppers clarify the speed of each motor and also clarify the capacitor for the new motor..If he did something to the fan blades because the new motor was overheating, my money says the new motor has a higher rpm than the old one. You're probably going to have to replace the fan blade if he cut or bent it.
he
rnelson
08-30-07, 11:13 AM
Hi DaddyJohn,
The RPMs are the same on both motors (825). I do have the original fan. First the tech used the original fan with the new motor and it overheated, so then he got a new lighter fan (mine was older and much heavier?) and he decreased the length of the blades by about an inch to help reduce the strain on the motor, but it still over heats.
I'm thinking these things could be an issue:
1. The capacitor, how can I check if it is good/correct one?
2. Replace the "cracked" 30 A, 3-fuse, 3 phase quick disconnect?
3. Check the Voltage going to the motor? Amps are fine at 2.2
4. Should the fan be blowing the air towards the motor or away from the motor?
Thanks for your help.
The RPMs are the same on both motors (825). I do have the original fan. First the tech used the original fan with the new motor and it overheated, so then he got a new lighter fan (mine was older and much heavier?) and he decreased the length of the blades by about an inch to help reduce the strain on the motor, but it still over heats.
I'm thinking these things could be an issue:
1. The capacitor, how can I check if it is good/correct one?
2. Replace the "cracked" 30 A, 3-fuse, 3 phase quick disconnect?
3. Check the Voltage going to the motor? Amps are fine at 2.2
4. Should the fan be blowing the air towards the motor or away from the motor?
Thanks for your help.
mattison
08-30-07, 12:34 PM
It should be pulling the air through the coil, across the motor, then out the top.
jim-connor
08-31-07, 07:31 AM
Modifying the fan blade is not a good idea for several reasons. Making the blades smaller will cause the blade to become unbalanced. Also, while it may reduce the load on the fan motor, it will decrease the air flowing over the coil, this results in higher head pressure and increased work for the compressor. Your fan motor may or may not be cooler but your compressor will run hotter and your power consumption increased. Not a good trade off.
To check the capacitor, look at the nameplate requirement on the fan motor and compare it to what the label on the capacitor says. ALWAYS REPLACE THE CAPACITOR WHEN REPLACING A MOTOR. Using an old capacitor with a new motor is like putting used oil in a new car. The risk is not worth the possible savings.
You may need a different technician before you kill your compressor.
To check the capacitor, look at the nameplate requirement on the fan motor and compare it to what the label on the capacitor says. ALWAYS REPLACE THE CAPACITOR WHEN REPLACING A MOTOR. Using an old capacitor with a new motor is like putting used oil in a new car. The risk is not worth the possible savings.
You may need a different technician before you kill your compressor.
daddyjohn
08-31-07, 12:49 PM
Modifying the fan blade is not a good idea for several reasons. Making the blades smaller will cause the blade to become unbalanced. Also, while it may reduce the load on the fan motor, it will decrease the air flowing over the coil, this results in higher head pressure and increased work for the compressor. Your fan motor may or may not be cooler but your compressor will run hotter and your power consumption increased. Not a good trade off.
To check the capacitor, look at the nameplate requirement on the fan motor and compare it to what the label on the capacitor says. ALWAYS REPLACE THE CAPACITOR WHEN REPLACING A MOTOR. Using an old capacitor with a new motor is like putting used oil in a new car. The risk is not worth the possible savings.
You may need a different technician before you kill your compressor.
You mentioned in one post that the tech reversed the airflow of the fan blades. As mentioned, these motors are AIR-OVER motors, they have to be in the airstream of the air being blown. Usually, air is sucked in thru the coil, then flows over the motor, then out of the unit. That airstream cools the motor. So, you 4 things to check/do:
1. is the capacitor for the fan new motor the right size? Look at the label on the motor, it will indicate what size capacitor to use. For example, a 5mfd [it might say uf, same thing] 370vac capacitor is a common one used on outdoor unit fan motors. Check the label on the new motor to see what size the motor needs. As others have said, the new motor should have been installed with a new capacitor even if the old one was still good and the right size.
2. Is the air flow going in the right direction? It has to flow over the motor to cool the motor. I really can't say towards or away without seeing the unit.
3. One more specification to check. Outdoor unit motors need to have a 60degreesC ratng. If the replacement motor has a 40 degree rating, it will overheat. It's on the label, llok for it and compare both motors.
4. reinstall the original fan blade if it's not all bent up from removing it. The weight is an insignificant factor. It's number of blades and the pitch of the blades that counts. Cutting the blades like he did ruined the new one.
This so called tech has taken a simple job to new heights of, well I better not say...
To check the capacitor, look at the nameplate requirement on the fan motor and compare it to what the label on the capacitor says. ALWAYS REPLACE THE CAPACITOR WHEN REPLACING A MOTOR. Using an old capacitor with a new motor is like putting used oil in a new car. The risk is not worth the possible savings.
You may need a different technician before you kill your compressor.
You mentioned in one post that the tech reversed the airflow of the fan blades. As mentioned, these motors are AIR-OVER motors, they have to be in the airstream of the air being blown. Usually, air is sucked in thru the coil, then flows over the motor, then out of the unit. That airstream cools the motor. So, you 4 things to check/do:
1. is the capacitor for the fan new motor the right size? Look at the label on the motor, it will indicate what size capacitor to use. For example, a 5mfd [it might say uf, same thing] 370vac capacitor is a common one used on outdoor unit fan motors. Check the label on the new motor to see what size the motor needs. As others have said, the new motor should have been installed with a new capacitor even if the old one was still good and the right size.
2. Is the air flow going in the right direction? It has to flow over the motor to cool the motor. I really can't say towards or away without seeing the unit.
3. One more specification to check. Outdoor unit motors need to have a 60degreesC ratng. If the replacement motor has a 40 degree rating, it will overheat. It's on the label, llok for it and compare both motors.
4. reinstall the original fan blade if it's not all bent up from removing it. The weight is an insignificant factor. It's number of blades and the pitch of the blades that counts. Cutting the blades like he did ruined the new one.
This so called tech has taken a simple job to new heights of, well I better not say...