Ask Me Help Desk - Diagnosing failing condenser fan

This is my first experience working on any kind of HVAC unit. I'm having trouble with my condenser fans. I have an outdoor unit of unknown age. It's a 2-fan unit that says "RUUD Acheiver 12" on the top. Recently, one of the fans started making squeaking/screeching noises when turning on and off and sometimes when running, too. Now it doesn't seem to be running at all. The other fan works fine most of the time, but just today, I noticed that it is sometimes failing to come on as well. The compressor seems to be fine, since when the fan(s) work, the unit cools effectively.

Today, I went out when the one fan was stalled and the other was running. I reached through the grill with a plastic knife and tried spinning the blades in both directions. It spun freely both ways. When I was spinning it opposite of the direction it is supposed to run, I noticed a slight grinding sound every few seconds, and when the sound occurred, the blade would slow, like the motor was trying to get the blade going in the proper direction, but it barely had enough traction to move it at all. I've also opened the unit up (after pulling the power disconnect), and the fans spin freely by hand with no noticeable resistance, so they're not completely bound. The fan motors appear to me to be sealed with no way of lubricating them.

I've been browsing through the posts here from people who have problems with their condenser fans, and a common recommendation I see is to replace the run capacitor. I've identified the run capacitors for each fan. I just have a few related questions.

1) Given the situation I described, does it seem like it could be a problem with the capacitors? What else might it be, and how could I check for other problems?

2) One of the capacitors apparently had its marking printed directly on the casing and is mostly rusted over, so I can barely read any of the markings on it. The fan attached to that capacitor says, "CAP: 5/370@230 7.5/370@208V" on it. I'm guessing this is the capacitor rating, and I'm also guessing it means I need a 5 MFD 370 VAC capacitor, but I'm not sure if this is a 230V system. How can I verify this?

3) The compressor capacitor (at least I'm pretty sure that's what it is) is also completely rusted over externally but has a readable paper label. Should I replace this, too? (I don't have a multimeter to test them with.)

4) Is a dual capacitor better than single capacitors? Should I prefer one over another?

5) What kind of store should I look for to buy these things at? There's a Grainger store nearby. What is your preference?

I have pictures of everything if needed.

Quote:

Originally Posted by zzantozz

This is my first experience working on any kind of HVAC unit. I'm having trouble with my condenser fans. I have an outdoor unit of unknown age. It's a 2-fan unit that says "RUUD Acheiver 12" on the top. Recently, one of the fans started making squeaking/screeching noises when turning on and off and sometimes when running, too. Now it doesn't seem to be running at all. The other fan works fine most of the time, but just today, I noticed that it is sometimes failing to come on as well. The compressor seems to be fine, since when the fan(s) work, the unit cools effectively.

Today, I went out when the one fan was stalled and the other was running. I reached through the grill with a plastic knife and tried spinning the blades in both directions. It spun freely both ways. When I was spinning it opposite of the direction it is supposed to run, I noticed a slight grinding sound every few seconds, and when the sound occurred, the blade would slow, like the motor was trying to get the blade going in the proper direction, but it barely had enough traction to move it at all. I've also opened the unit up (after pulling the power disconnect), and the fans spin freely by hand with no noticeable resistance, so they're not completely bound. The fan motors appear to me to be sealed with no way of lubricating them.

I've been browsing through the posts here from people who have problems with their condenser fans, and a common recommendation I see is to replace the run capacitor. I've identified the run capacitors for each fan. I just have a few related questions.

1) Given the situation I described, does it seem like it could be a problem with the capacitors? What else might it be, and how could I check for other problems?

2) One of the capacitors apparently had its marking printed directly on the casing and is mostly rusted over, so I can barely read any of the markings on it. The fan attached to that capacitor says, "CAP: 5/370@230 7.5/370@208V" on it. I'm guessing this is the capacitor rating, and I'm also guessing it means I need a 5 MFD 370 VAC capacitor, but I'm not sure if this is a 230V system. How can I verify this?

3) The compressor capacitor (at least I'm pretty sure that's what it is) is also completely rusted over externally but has a readable paper label. Should I go ahead and replace this, too? (I don't have a multimeter to test them with.)

4) Is a dual capacitor better than single capacitors? Should I prefer one over another?

5) What kind of store should I look for to buy these things at? There's a Grainger store nearby. What is your preference?

I have pictures of everything if needed.

Make sure both fan motors are getting power from the unit.

The MFD rate of the capacitor should match the motor and the operating voltage of the unit. (The fan attached to that capacitor says, "CAP: 5/370@230 7.5/370@208V" on it.) If your unit operates on 230 volts it will be a 5 MFD and if 208 it will be a 7.5 MFD. You will need a meter to see exactly what voltage it. Any new motor you replace will need a NEW capacitor that matches that new motor.

If you do not have an accurate capacitor tester then the only option is to replace the capacitor to see if that is the problem or in your case. If that does not work then you will be replacing the motor. From what you said I would just replace the motor to start with.

Grainger should have what you need.

Quote:

Originally Posted by hvac1000

From what you said I would just replace the motor to start with.

Grainger should have what you need.

Okay, I've been looking at replacement motors. There's a pretty wide range of prices. Should I just go with the lowest price, or are there brands to stay away from, or what?

That is a loaded question since most of the cheap motors are made in China and some of the good brand names also. Emerson/GE/and other name brands should be OK.

I'll attempt to fill in some blanks. The voltage rating doesn't have to be exact. It's usually 370V or so for 240 V systems because the circuit now consists of inductance, capacitance and resistance and the voltages and current can be out of phase.

Your problem is friction and since the bearings are not replaceable, you have to replace the motor.

When you replace the motor, get the suggested capacitor. Probably a single.

Age of the capacitor may help you to decide if replacing the compressor cap is worth it too.

Duals are cheaper for the manufacturer, but if you get singles you need the brackets.

Watch routing of wires and the drains and make sure drip legs are in place when replacing the motor. Some universal replacements have the ability to change the direction with a plug.

Well, I got a Dayton 4M223J motor from Grainger and installed it along with a new capacitor. I hooked up the motor to test it without the fan, and it seemed to start and run fine. After mounting the motor, attaching the fan and putting everything back together, the first time I turned the unit back on, the fan didn't start. Giving it a little push started it turning, but I soon found that it turned in whichever direction I pushed it! When I turned it off and back on, it wouldn't start on its own again, but later, after it had run for a while and the unit cycled off and on normally, it did start up on its own.

I don't see how it could possibly be wired wrong. It's a 4-wire motor with purple, black, brown, and brown-white. The panel says brown and brown-white go to the capacitor, purple is "common" connected to L1, and black is connected to L2. There's a green ground, too, of course. I put the browns to the capacitor, the purple to the contactor where the old fan's purple wire was attached, and the black to what I believe is called the LAR where the old fan's black wire was attached.

Did I hook something up wrong? Is something else broken? Did I get a bad motor? What can I do to diagnose further?

Also, could someone explain the usage of "common", "L1", and "L2" here? I've seen descriptions of L1 and L2 before. Isn't there also an S1 and S2?

Additional note: I checked on it again this morning, and while it was off, the fan on the new motor was moving. It spun slowly a little, stopped, then spun some more slowly. I suppose it could've been the wind, which is blowing slightly? It seems unlikely. Is that an indication of something?

Line 1 = L1

Line 2 = L2

These are the two legs of 120 volts that when used together equals 240 volts used to power the outside A/C system.

The line side is the imput power side of the contactor.

The other side of the contactor is called the load side or switch side. The load side is used to attach the compressor and fan motor to the contactor. This is where the term of S1 and S2 come from. They are the switch contacts of the contactor.

So the new fan is saying I should hook the two wires up to the input side of the contactor? That means the fan would always run, right? Wouldn't the correct way to be to hook a wire from the fan to each of the two outputs of the contactor--S1 and S2 from your description? That's what seems to make sense, and if that's right, then the old fans were connected wrong all along, and that's probably what my problem was from the start.

Quote:

Originally Posted by zzantozz

So the new fan is saying I should hook the two wires up to the input side of the contactor? That means the fan would always run, right? Wouldn't the correct way to be to hook a wire from the fan to each of the two outputs of the contactor--S1 and S2 from your description? That's what seems to make sense, and if that's right, then the old fans were connected wrong all along, and that's probably what my problem was from the start.

Line 1 = L1

Line 2 = L2

These are the two legs of 120 volts that when used together equals 240 volts used to power the outside A/C system.

The line side is the imput power side of the contactor.

The other side of the contactor is called the load side or switch side. The load side is used to attach the compressor and fan motor to the contactor. This is where the term of S1 and S2 come from. They are the switch contacts of the contactor.

If you read what I posted you do not hook the motor power wires to the imput side of the contactor. You hook them to the load side or switch side since they are supposed to only be powered when the unit is running.

You must have something wired wrong to have the motor not start and run with out assistance. Recheck your capacitor wires and make sure thery are attached to the NEW capacitor you bought for the new motor. You always buy a new capacitor for a new motor and the new capacitor has to be sized as per the new motor instructions..

Quote:

Originally Posted by hvac1000

If you read what I posted you do not hook the motor power wires to the imput side of the contactor. You hook them to the load side or switch side since they are supposed to only be powered when the unit is running.

You must have something wired wrong to have the motor not start and run with out assistance. Recheck your capacitor wires and make sure thery are attached to the NEW capacitor you bought for the new motor. You always buy a new capacitor for a new motor and the new capacitor has to be sized as per the new motor instructions..

Yes, new motor, new capacitor. I did try it with the old capacitor, too, though, with the same results.

The appropriate wires from the fan are attached to the capacitor (brown and brown/white). That leaves the purple and the black, which the diagram on the fan says should go to L1 (also says "Common") and L2, respectively. According to your description, that should be the inputs, which plainly can't be right, so I still can't figure out what it's trying to tell me.

What I did was hook the purple and black to where the old motor was hooked up. That was with the purple wire going to the switch side of the contactor and the black wire going to something right next to the contactor, which I think is the LAR (Low Ambient Relay) from the wiring diagram inside the unit. I guess I'll go move the black one from that other thing over to the contactor and see what happens.

Another thing that's been bugging me: should the capacitor be getting power all the time, or only when the unit is running? It seems like if the capacitor is for getting the fan started, it should be charging when the fan isn't running.

Bottom line: there are four wires on the new motor. That means two go the capacitor, and two go to the contactor?

Bottom line: there are four wires on the new motor. That means two go the capacitor, and two go to the contactor?

Yes to the new capacitor rated to work with your new motor and the other two goes to the contactor.