ReplyAre you losing voltage at G when the blower cuts out?
The only advice I could give without being there is just look at the wiring diagram and trace back what's providing 24 volts to the coil.
Professional Member*
Carrier 48TFE012-A-611 ser 1004G50704
This unit will run for about 1 minute normally and then the blower will cut out. The contactor for the blower motor has 27 volts at the coil until it cuts out. Then it shows no low voltage. The compressors and condenser fan motors will continue to run until the unit cuts out on low pressure. The blower will not come back on until you cut power to it from the disconnect and then reestablish power. It looks like to me, the only thing that could cause this condition is a bad board. I haven't seen this before and was hoping that one of you have. If you need all of the gauge readings and etc, I have them but I didn't post them since I don't think they are relevant to the problem. Thanks in advance!
Professional Member
Are you losing voltage at G when the blower cuts out?
The only advice I could give without being there is just look at the wiring diagram and trace back what's providing 24 volts to the coil.
Professional Member
Nevermind that question...Forgot you need 24 volts to G on a carrier for the compressor to start.
Professional Member*
Originally Posted by flanders
Does that unit have the fan contactor/ timer assembly. It just a fan relay with a small board
attached to it.
If it does or it gets it out put from a board jump the fsn coil wire to R to keep it running and then monitor the out put at the board.
Not much to those Carrier RTUs.
Professional Member*
Go to the economiser board if it has the 4 LED`s on it and bypass the G terminal so the board doesn`t control the fan. Then look for corrosion on it. Change as neccessary.
Global Moderator
Check the fan logic for power in and out also the blower relay. Check t-stat as well.
Professional Member*
Thanks for the replies. I'm going back today so I'll let you know if your suggestions worked.
God Speed, Jim. We'll miss you - 2-26-23
What did you find.
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Sorry that it took me so long to reply. When I arrived back on the scene the unit had new problems. Blower still was not running but now the reset button on the economizer was tripped. I reset it and the unit cycled off on high pressure. I found that 1 of the 2 condenser motors is bad. I replaced the motor and dual capacitor (10/10 mfd) on Friday. With the economizer reset and the new condenser motor, it seemed to operate fine. I waited for about 30 minutes and then I split. I am going back this afternoon to check on it again (and drop the bill off). Even if everything is fine, I am still concerned with the economizer reset being tripped. I will keep you posted.
P.S. Something else that I found was that someone jumped out the board where the 5V fuse is supposed to be so there must have been a low voltage problem before me.
Global Moderator
Or they did not have a replacement fuse. Are you planning on replacing it ?P.S. Something else that I found was that someone jumped out the board where the 5V fuse is supposed to be so there must have been a low voltage problem before me.
Professional Member*
I don't know the reason why it is jumped out. I am going to put a fuse in but I want to rectify the problems at hand first.
Global Moderator
You could throw on a "lil popper 5 amp" till you find your problem. Provided the first one you try blows.
AOP Committee/Professional Member*
That must be a Resi thing. Not true on the RTU's.
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
RSES CMS, HVAC Electrical Specialist
Member, IAEI
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AOP Committee/Professional Member*
Do you have a pic of where you "reset the economizer?" That's a new one for me...Sorry that it took me so long to reply. When I arrived back on the scene the unit had new problems. Blower still was not running but now the reset button on the economizer was tripped. I reset it and the unit cycled off on high pressure. I found that 1 of the 2 condenser motors is bad. I replaced the motor and dual capacitor (10/10 mfd) on Friday. With the economizer reset and the new condenser motor, it seemed to operate fine. I waited for about 30 minutes and then I split. I am going back this afternoon to check on it again (and drop the bill off). Even if everything is fine, I am still concerned with the economizer reset being tripped. I will keep you posted.
P.S. Something else that I found was that someone jumped out the board where the 5V fuse is supposed to be so there must have been a low voltage problem before me.
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
RSES CMS, HVAC Electrical Specialist
Member, IAEI
AOP Forum Rules:
AOP Committee/Professional Member*
Good idea. The lil popper is perfect for the Carrier RTU board.
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
RSES CMS, HVAC Electrical Specialist
Member, IAEI
AOP Forum Rules:
Professional Member
some Carrier RTU's do need 24v at G for the compressor to run, I've worked in a few of them.
AOP Committee/Professional Member*
Post a model # when you have a chance. I've never seen one.
[Avatar photo from a Florida training accident. Everyone walked away.]
2 Tim 3:16-17
RSES CMS, HVAC Electrical Specialist
Member, IAEI
AOP Forum Rules:
Global Moderator
So if you were to set the t-stat to fan on the compressor will start ?
Or are you saying Y & G at stat ?
Professional Member
nopeSo if you were to set the t-stat to fan on the compressor will start ?
Or are you saying Y & G at stat ?mechanical cooling control interlocked with fan contractor, very simple stuff! sooner or later you'd run into one.
God Speed, Jim. We'll miss you - 2-26-23
If you jumper R to Y at the board of the RTU. The compressor won't run, unless the blower contactor is in also.So if you were to set the t-stat to fan on the compressor will start ?
Or are you saying Y & G at stat ?
First time you run into one, it throws you off.
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