Air Conditioning - Carrier outdoor unit problem?
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TrafficTech
05-07-09, 05:10 PM
Good evening everyone. I work in Traffic Signals for a very cheap city. A city that wont even send its own HVAC techs to trouble shoot its own equipment.
In our Traffic comm hub we have a carrier #38YCC018300 to keep our switch gear cool. Last week while doing maintenance on the summit 48i switches I noticed the room wasn't very cool.
I checked the outside unit and found the condensing fan was locked up and the capacitor bloated. I replaced both with parts from Grainger and everything works great.
The room stays nice and cold.
My problem in the condensing fan is humming while the AC is turned off at the thermostat. You cant hear the hum but you can feel it when touched, also its a bit warm but not super hot even after its been off for a while.
Thanks for any help you can provide.
In our Traffic comm hub we have a carrier #38YCC018300 to keep our switch gear cool. Last week while doing maintenance on the summit 48i switches I noticed the room wasn't very cool.
I checked the outside unit and found the condensing fan was locked up and the capacitor bloated. I replaced both with parts from Grainger and everything works great.
The room stays nice and cold.
My problem in the condensing fan is humming while the AC is turned off at the thermostat. You cant hear the hum but you can feel it when touched, also its a bit warm but not super hot even after its been off for a while.
Thanks for any help you can provide.
HVAC Mech.
05-07-09, 07:06 PM
If the fan motor is 120v. then the neutral leg may be the one being switched by the contactor instead of L1. This would make the motor "live" to ground.
If 208v. 1 phase, then L1 & L2 are both used as hot legs, and the contactor may switch one or both legs. With the compressor, this is done so one leg acts as a crankcase heater (through milliamp leakage thru the winding insulation to ground) but with the cond. fan motor, the leg with the capacitor on it should be switched.
Tom Beer 4U2
If 208v. 1 phase, then L1 & L2 are both used as hot legs, and the contactor may switch one or both legs. With the compressor, this is done so one leg acts as a crankcase heater (through milliamp leakage thru the winding insulation to ground) but with the cond. fan motor, the leg with the capacitor on it should be switched.
Tom Beer 4U2
TrafficTech
05-08-09, 03:56 AM
If the fan motor is 120v. then the neutral leg may be the one being switched by the contactor instead of L1. This would make the motor "live" to ground.
If 208v. 1 phase, then L1 & L2 are both used as hot legs, and the contactor may switch one or both legs. With the compressor, this is done so one leg acts as a crankcase heater (through milliamp leakage thru the winding insulation to ground) but with the cond. fan motor, the leg with the capacitor on it should be switched.
Tom Beer 4U2
Tom, Thank you for your reply. what you're saying makes since I'm going out this morning to check how the 24v RBM relay is wired.
The unit is 208v, sorry I didn't mention it in my first post.
If 208v. 1 phase, then L1 & L2 are both used as hot legs, and the contactor may switch one or both legs. With the compressor, this is done so one leg acts as a crankcase heater (through milliamp leakage thru the winding insulation to ground) but with the cond. fan motor, the leg with the capacitor on it should be switched.
Tom Beer 4U2
Tom, Thank you for your reply. what you're saying makes since I'm going out this morning to check how the 24v RBM relay is wired.
The unit is 208v, sorry I didn't mention it in my first post.
TrafficTech
05-08-09, 05:26 PM
I took a couple of pic's to try and explain what I have at the unit.
From what I can tell everything is wired as per the wiring diagram .
http://i630.photobucket.com/albums/uu22/TrafficControlTech/Diagram.jpg
http://i630.photobucket.com/albums/uu22/TrafficControlTech/L1L2.jpg
From what I can tell everything is wired as per the wiring diagram .
http://i630.photobucket.com/albums/uu22/TrafficControlTech/Diagram.jpg
http://i630.photobucket.com/albums/uu22/TrafficControlTech/L1L2.jpg
HVAC Mech.
05-09-09, 05:00 AM
I see power supplied all the time to the run winding of the OFM thru the unswitched leg/ yellow wire to the OFM. The switched leg contact is shorted thru the CCH, when the CCH switch is made. This supplies some voltage thru the normally closed contacts on the PC board.
The only way to eliminate this is to disconnect the CCH wires (red & black) from 11 & 21 on the contactor. Being a heat pump, this would be OK during the summer, but you'd have to remember to reconnect for cold weather, to prevent crankcase oil dilution due to refrigerant migration. Refr. migrates to the coldest spot in the system.
TomBeer 4U2
The only way to eliminate this is to disconnect the CCH wires (red & black) from 11 & 21 on the contactor. Being a heat pump, this would be OK during the summer, but you'd have to remember to reconnect for cold weather, to prevent crankcase oil dilution due to refrigerant migration. Refr. migrates to the coldest spot in the system.
TomBeer 4U2
TrafficTech
05-09-09, 09:46 AM
Tom, Thanks for the reply but that didn't work.
I disconnected both wires (red and black) from 11 and 21 on the contactor and still have humming at the OFM.
Correct me if I'm wrong but the only way I see to eliminate the constant power going to the OFM is to maybe wire in a 120v relay with a 24v trigger ( I think the thermostat runs on 24v) between one or both yellow leads coming from 23 of the contactor creating switching on L2. .???. (Yellow leads going to the Cap and Comp)
PS. I never really run the heater in the room, we never get much of a winter in FL.
Thanks again for your help.
I disconnected both wires (red and black) from 11 and 21 on the contactor and still have humming at the OFM.
Correct me if I'm wrong but the only way I see to eliminate the constant power going to the OFM is to maybe wire in a 120v relay with a 24v trigger ( I think the thermostat runs on 24v) between one or both yellow leads coming from 23 of the contactor creating switching on L2. .???. (Yellow leads going to the Cap and Comp)
PS. I never really run the heater in the room, we never get much of a winter in FL.
Thanks again for your help.
HVAC Mech.
05-10-09, 07:11 AM
The only other thing I can think of to do, is to replace the contactor with a DPST type. Then the CCH wouldn't be energised during the off cycle. If you never use the HP function, I wouldn't worry about it.
The OFM side of the cap could be leaky, too. Remove the single lead to the OFM and check the cap with an ohmmeter on 100k. After an initial charging (from the batteries in the ohmmeter) it should return to 0 ohms. Also check ohms to ground - should be 0.
TomBeer 4U2
The OFM side of the cap could be leaky, too. Remove the single lead to the OFM and check the cap with an ohmmeter on 100k. After an initial charging (from the batteries in the ohmmeter) it should return to 0 ohms. Also check ohms to ground - should be 0.
TomBeer 4U2
daddyjohn
05-12-09, 09:26 PM
It looks to me like the circuit for the CCH is thru the run winding of the COMPRESSOR motor when CHS closed. This is assuming that the internal protector in the compressor is closed. You removed the CCH circuit wires at the contactor and the humming is still there? Are the contacts on the contactor breaking completely? Is this unit grounded all the way back to the panel? You sure? Take your Amprobe and see which wires on the OFM are drawing current.