HVAC Tech? Anyone?

[dorkiedoode]

This past week I found that my condenser fan would not turn on by itself. With a little help from my screwdriver I gave it a push and it starts to spin normally then slow down because the fan starts to overheat. Looking through the internet I found that replacing the capacitor would help. I bought a new capacitor with the same MFD rating/volts and now the fan would start up but spin slower than usual, ending up overheating as well. The new replacement capacitor is a dual cap 50/5mfd.

the original wiring for the AC was HERM and COMMON to a dual capacitor and the fan has its own separate cap.

Overall, if i wire the motor to a dual cap it will not work correctly. However if i wire it to a single cap then it will work correctly. Anyone know why? same rating and everything.

 

[dishdude]

Sounds like the fan motor is shot. Maybe the bad cap took it out?

I am not an HVAC Tech, just adding my 2 cents

 

[dorkiedoode]

Originally Posted By: dishdude
Sounds like the fan motor is shot. Maybe the bad cap took it out?

I am not an HVAC Tech, just adding my 2 cents

That is what i thought. However the fan is running perfectly fine with the old set up currently. Not sure why it didn't start in the first place. Maybe it is because we have not used the AC for more than 6 months.

 

[bullwinkle]

The dual cap is just 2 capacitors in the same housing, must be wired wrong-but if it works with 2 individual run caps I'd say let 'er rip!

 

[river_rat]

Originally Posted By: dishdude
Sounds like the fan motor is shot. Maybe the bad cap took it out?

I am not an HVAC Tech, just adding my 2 cents

I used to be an HVAC tech (and taught it for a couple years at a vocational college, and that is my guess, too.

 

[UNC017]

The connection to the old cap was probably just bad. Removing it and re-installing it made the connection good again.

If the bad spot is where the cap terminal attaches to the cap itself, it probably won't last long :-/

When you connected to the dual cap, are you SURE you weren't hooked to the larger cap, or to the two caps in series? Either one would cause the problem you saw.

 

[dorkiedoode]

Originally Posted By: 440Magnum
The connection to the old cap was probably just bad. Removing it and re-installing it made the connection good again.

If the bad spot is where the cap terminal attaches to the cap itself, it probably won't last long :-/

When you connected to the dual cap, are you SURE you weren't hooked to the larger cap, or to the two caps in series? Either one would cause the problem you saw.

I agree, I do recall cutting off old wires and adding in new terminals which probably made the connection better to the old cap. When I installed the new cap, the old caps were removed and stored for testing when I get a new DMM. I installed the new cap the same way they did but yield different results. Brn and Brn/white on Fan, compressor to herm, and T1 to common.

 

[dorkiedoode]

Originally Posted By: river_rat
Originally Posted By: dishdude
Sounds like the fan motor is shot. Maybe the bad cap took it out?

I am not an HVAC Tech, just adding my 2 cents

I used to be an HVAC tech (and taught it for a couple years at a vocational college, and that is my guess, too.

Currently the motor runs fine. I left it on for a few hours yesterday and it is still running today. It might be my wiring but i'm not sure.

Old wiring

compressor blue to dual cap HERM
T1 on contact to dual cap COMMON
brn and brn/white to a separate cap

New wiring

compressor blue to new dual cap HERM
T1 on contact to new dual cap common
brn and brn/white to new dual cap FAN

 

[JHZR2]

The cap is for soft starting - limiting onrush current at startup. It sounds to me like your bearings are shot and so the fan is toast. If anything I'd try to clean and lube it, but don't count on a lot of life...

 

[dorkiedoode]

Originally Posted By: JHZR2
The cap is for soft starting - limiting onrush current at startup. It sounds to me like your bearings are shot and so the fan is toast. If anything I'd try to clean and lube it, but don't count on a lot of life...


We do plan on replacing the fan soon. It was just strange why the same capacitor produces different results. I was just curious to know why :]

I have been reading that many people recommend replacing the fan with a similar HP rating and everything. What I discover is that the previous owner replaced the fan with a different, more stronger motor than before. The original fan was 1/8HP and the new one is 1/4HP. Will this be a problem? I spent a lot of time trying to find the original fan specs but now I can't find anything that is similar to it. the original fan is

(http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280660891394&ssPageName=STRK:MEWAX:IT

 

[UNC017]

Originally Posted By: JHZR2
The cap is for soft starting - limiting onrush current at startup.



No, its not. This is AC, not DC. The cap is there to provide a phase shift on the secondary windings so that you actually get a "rotating" magnetic field around the motor armature instead of one that just flip-flops back and forth. All single-phase motors have to have some phase-shifting mechanism in order to start, three-phase motors don't because the coil sets are naturally 120-degrees out of phase and inherently produce a rotating magnetic field. Very small single-phase motors use "shading coils" built into the stator windings, larger motors use start and run capacitors wired to a secondary set of windings in the motor. A large fan motor is typically a "PSC" (permanent split capacitor) that leaves the same capacitor in the circuit for starting and for running. Hermetic compressors usually have a separate start and run capacitor and a potential relay to disengage the start capacitor after the motor comes up to speed.

 

[Dave Sherman]

Originally Posted By: 440Magnum
Originally Posted By: JHZR2
The cap is for soft starting - limiting onrush current at startup.



No, its not. This is AC, not DC. The cap is there to provide a phase shift on the secondary windings so that you actually get a "rotating" magnetic field around the motor armature instead of one that just flip-flops back and forth. All single-phase motors have to have some phase-shifting mechanism in order to start, three-phase motors don't because the coil sets are naturally 120-degrees out of phase and inherently produce a rotating magnetic field. Very small single-phase motors use "shading coils" built into the stator windings, larger motors use start and run capacitors wired to a secondary set of windings in the motor. A large fan motor is typically a "PSC" (permanent split capacitor) that leaves the same capacitor in the circuit for starting and for running. Hermetic compressors usually have a separate start and run capacitor and a potential relay to disengage the start capacitor after the motor comes up to speed.



Thank you! Somebody got it right. Lots of bad info being handed out otherwise. The fan motor would use a run capacitor, and the replacement capacitor MUST have the same capacitance (microfarads) as the old one. Higher voltage rating is OK, lower voltage rating is not OK. If it's a dual cap unit, DON'T connect them together, just use one of them. If it's still having problems, then more likely your motor bearings are going bad. Don't just guess at how to wire electric motors if you don't know what you are doing!

 

[dorkiedoode]

Originally Posted By: Dave Sherman
Originally Posted By: 440Magnum
Originally Posted By: JHZR2
The cap is for soft starting - limiting onrush current at startup.



No, its not. This is AC, not DC. The cap is there to provide a phase shift on the secondary windings so that you actually get a "rotating" magnetic field around the motor armature instead of one that just flip-flops back and forth. All single-phase motors have to have some phase-shifting mechanism in order to start, three-phase motors don't because the coil sets are naturally 120-degrees out of phase and inherently produce a rotating magnetic field. Very small single-phase motors use "shading coils" built into the stator windings, larger motors use start and run capacitors wired to a secondary set of windings in the motor. A large fan motor is typically a "PSC" (permanent split capacitor) that leaves the same capacitor in the circuit for starting and for running. Hermetic compressors usually have a separate start and run capacitor and a potential relay to disengage the start capacitor after the motor comes up to speed.



Thank you! Somebody got it right. Lots of bad info being handed out otherwise. The fan motor would use a run capacitor, and the replacement capacitor MUST have the same capacitance (microfarads) as the old one. Higher voltage rating is OK, lower voltage rating is not OK. If it's a dual cap unit, DON'T connect them together, just use one of them. If it's still having problems, then more likely your motor bearings are going bad. Don't just guess at how to wire electric motors if you don't know what you are doing!

Guys I contacted the person who sold me the cap and did some more research on the wiring. I did not wire the caps together if that's what you are thinking( i dont know who said that in the first place?). And yes I got the same uF and a higher voltage cap than rated, like i mentioned above. The only problem was that I wired the 2 Brn wire together like they did on a separate cap on a dual cap.

Solution: When using a dual cap you only wired one brn wire. When you are using a separate cap for the fan you wire in two.

The motor still runs fine. If it dies then i'll buy a new one. We barely use the AC anyways. Ran it all day yesterday!

 

[brianl703]

Originally Posted By: dorkiedoode

Old wiring
brn and brn/white to a separate cap

New wiring
brn and brn/white to new dual cap FAN


This is your problem.

 

[dorkiedoode]

correct! No one looks at the wiring