The condenser fan went out on my antique heat pump system the other day.
It has acted up on me once or twice before…just stopped turning and I had to turn the blades by hand to get it started. Last weekend, it started squealing occasionally so I knew it was getting ready to go.
It lasted until about midday Sunday. I finally got a replacement today and got it fixed. Coolness. Literally.
Those of you who read this blog for gun stuff and/or my so obvious political savvy and superior wisdom (that’s a joke), you can stop reading here. I’m going to document a few things about the motor change that I learned or had trouble with so if anyone ever has the same questions or troubles and turn to the interwebtubes for help…here it is:
Electricity will kill you dead. ALWAYS turn off all system power switches and disconnect the power at the breaker box or fuse panel before doing ANY work on electrical systems. If you are not ABSOLUTELY CERTAIN that power is completely removed from the system, DO NOT PROCEED. Call a professional before you kill yourself.
First of all, the specifics. This is an old Carrier split system heat pump with a round outdoor unit (model number 38QN024310 if you’re keeping score at home). The fan is installed vertically with the shaft up. The original motor is a General Electric model 5KCP39GGK779CS. Apparently, this is an obsolete model because I couldn’t find one anywhere. There were similar GE fans listed as OEM replacements for this model of condenser unit, but they were extremely expensive ($200 to $300). I decided to go with a generic Fasco replacement motor.
I ordered from emotorstore.com and got the fan for $52.85 and a new dual run capacitor in the right size for $10.56. Total cost with shipping $74.22. I ordered on Monday, it was shipped on Tuesday and it arrived today (Thursday). Excellent responsiveness.
It seems that condenser fan motors are pretty exclusively PSC (Permanent Split Capacitor) motors. (click all pix to make bigger, the ruler is a standard 1″ x 12″ metal ruler for scale…I only took pix of the old stuff, I was more concerned with getting the replacements installed than taking pictures of the pretty new motor and capacitor)
To make sure you order the right motor, you need to know:
- The horsepower rating (I needed a 1/4 hp)
- The rpm (1075)
- Single speed or dual speed (single)
- Shaft size (1/2″)
- Fan body dimensions and mounting type (5.5″ diameter, 4″ depth, band mount)
- Voltage (230v)
- Voltage frequency (In the US it’s always 60hz)
- And rotation (mine rotates CW when looking from the shaft end. Most of the replacements are reversible so you just need to be sure to set it for the correct rotation direction before installing).
The easiest way to get this information is off the label on the old motor. Removal of mine was fairly uneventful. The only tricky part was getting the fan blades off the shaft. The fan blade hub was rusted up pretty good. After taking the set bolt that locks the hub to the shaft off (it surprised me by coming out easily in spite of the rust), I squirted some penetrating oil in the hole and over the hub. After letting it sit for about 30 minutes (I’m impatient), I used a big socket that the shaft fit into and used that to give the blade hub a good whack or two to knock it loose. Once I got it loose, it came right off.
The Fasco motors all seem to come with extra long shafts so that you’d be sure to have plenty. I had to cut almost 4 inches off the shaft with a hacksaw to get it down to size.
The mounting arrangements can be unique so be sure to pick a motor that will fit your mounts, or you may have to buy or make a new mounting system. Luckily mine was a pretty simple mounting system, a band wrapped around the body of the motor secured by a pinch bolt. The band holds three “legs” in place which bolt to the top cover to suspend the fan in the center of the condenser coils.
For fans that will be exposed to the elements as in outdoor condenser units, you also have to be sure to pick a motor correct for the installation orientation. Motors that are installed with the shaft up (like mine) are closed at the top to prevent water intrusion, but are open on the bottom and sides. If you mount a shaft up motor incorrectly…horizontally or with the shaft down, water will get inside, ruin the motor, and possibly cause an electrical short which can result in a fire.
The capacitors are not overly expensive and are easy to replace. Every site I looked at when shopping for a motor listed the size of the capacitor that was needed for each fan somewhere on the page. Capacitors are rated by their capacitance in microfarads (MFD) and voltage handling capability in A/C Volts. The fan I ordered needed a 5M370v (5MFD, 370VAC). The proper capacitance rating is critical in ensuring that the motor runs correctly. Voltage rating isn’t as critical, but be aware that you can only go up in voltage rating, never down. In other words, you can use a 440VAC capacitor in a system that only needs a 370VAC, but not the reverse.
Many condenser units use a dual capacitor with one side used for the compressor and the other for the fan. Pictured is the old capacitor from my system. They basically just look like an oval metal can with wires connected to terminals on one end. If your system uses separate capacitors for the compressor and the fan, there will be two smaller capacitors but each will only have two terminals rather than one bigger capacitor with three terminals. Each terminal will have more than one connecting tab (usually four tabs per terminal) so there will probably be more than three wires connected to the capacitor.
There are a couple of options for replacing the capacitor. Even if your system uses a dual capacitor, you can buy a new single capacitor just for the fan. Basically, you disconnect the fan wiring from the old capacitor and hook it to the new capacitor. The fan side of the old capacitor will just not be connected.
If you decide to replace the dual capacitor completely, you will have to find the rating marked on the outside of the old capacitor. As you can see, mine was quite rusted and hard to read. I was able to decipher it using a magnifying glass under bright light, but don’t guess. If you can’t read it, as long as the capacitor is still working, your best bet is just to replace the fan side and leave the compressor side alone.
Since I was able to decipher mine, I went ahead and ordered the dual capacitor and replaced the whole thing. I needed a 25 MFD 370VAC capacitor for the compressor side, so I ordered a 25-5M370V. Apparently, emotorstore.com was out of the 370V’s and substituted a 25-5M440V in its place…remember, you can always use the higher voltage rated capacitor in place of the lower, but never the reverse.
OK. Parts are ordered. Now just sweat it out (literally) waiting for them to get here.
Upon receiving the Fasco fan and capacitor, I was in for a mild surprise. The old fan only had three wires connected to it. A Black, a Brown and a Yellow. The new fan had four wires: Black, White, Brown and Brown with a white stripe. (It also had a green and yellow wire for connecting to chassis ground and a pair of purple and a pair of yellow wires but those are only used to control the direction of rotation. Purple to Purple and Yellow to Yellow for CW rotation, or cross them for CCW rotation.)
The simple wiring diagram on the label of the motor showed white and black wires to be connected to power and the two brown wires connected to either side of the capacitor.
Now I had to figure out how to connect this four wire motor into my three wire condenser unit.
This schematic actually shows the entire installation including the thermostat and the indoor evaporator unit. I chopped it down to only show the part we’re worried about.
Click to make really big so you can see the details.
Luckily for me, I spent 20 years working on Aviation Electronics systems in the Navy and I have an associate’s degree in electronics so it wasn’t hard for me to decipher the schematic.
NOTE: I could just tell you what the solution to the dilemma was, however if your system is not exactly like mine, the solution I reached may not work for yours. To that end, I’m going to explain the basics of how the system works, what I did and why; that way if your system is a bit different, you may be able to use this information to figure out what you need to do to properly wire yours.
Although I imagine that all heat pump systems are similar, they may not be identical. If you try to hook yours up the way I did mine and it doesn’t work or fries your new motor…it’s not my fault. Do this at your own risk.
For those of you who don’t have the benefit of experience, I took the liberty of marking the schematic up a little to clarify. Please pardon my cartoonish arrows. I haven’t figured out how to do arrowheads in Gimp so I just freehand short lines to make them.
Click to make really huge…right click and select “open in a new window” so that you can flip back and forth between the schematic and this discussion.
On the top left, power comes in at L1 and L2 These are usually terminals, but on my unit they were just wirenut connections. The wire highlighted in yellow is considered the “common” side (which is really not true in this application because in household 230 Volt applications both sides are hot…they are each at 115v respectively but 180 degrees out of phase. When one line is at +115V the other line is at -115V, for a total of 230V).
Following the highlighted wire to the right, it passes through the contactor at terminal 23. The contactor is basically a big relay. The picture to the right is pretty close to what mine looks like. Basically, the contactor allows the thermostat on your wall to turn the compressor and condenser unit on and off without having those big, 230V power wires running to it. The Thermostat uses 24VAC as control wiring. The 24V signal from the thermostat energizes the relay, which basically closes the switch and sends 230V to the compressor and fan motor.
The part of the circuitry that isn’t highlighted isn’t important to this discussion, but this incoming power wire also goes to one side of the compressor and to some thermal protection circuitry.
Following the highlighted section down, this wire connects to the center terminal of the dual run capacitor. It also splits off from the center terminal of the capacitor and connects to the yellow “common” power wire on the condenser fan motor.
The other incoming power wire is highlighted in green. It comes in and passes through the contactor at terminals 11 and 21. It also connects to the other side of the thermal protection circuit and goes to the other power wire for the compressor. Following the highlighted part, it goes down through the contacts of the defrost relay. You only find defrost relays on heat pumps. During the winter, when the heat pump is set to “heat” mode, the defrost relay turns off the condenser fan for a period of time (usually for about ten minutes every hour). Another relay reverses the coolant flow during that time, but that’s on a different part of the schematic and not shown here. The combination of reversing the coolant flow and turning off the fan allows the condenser coils to heat up which prevents the unit from freezing up when it’s cold outside.
After passing through this relay, it then goes straight to the black “hot” power wire of the condenser fan motor.
The wire highlighted in purple (marked “brown” on the schematic, but actually kind of a dirty yellow on my actual unit) goes from the “fan” terminal of the capacitor to the brown capacitor wire on the motor.
So, in the three wire system, we have the black “hot” power wire, the yellow “common” power wire which also connects to the “common” side of the capacitor, and the brown wire which goes to the “fan” side of the capacitor.
Well, the diagram on the four wire motor shows the white going to the “common” power wire…so that one should connect to the yellow wire in the unit. The black goes to the “hot” power wire so it obviously connects to the black wire (highlighted in green on the schematic) in the unit. The brown wire goes to the “fan” side of the capacitor so it gets connected to the brown wire (highlighted in purple on the schematic) in the unit. The only one left is the brown and white…it is supposed to go to the “common” side of the capacitor, but the white fan motor wire (connected to the yellow wire in the unit) is already connected to that.
The obvious solution is to connect the brown and white and white fan motor wires together. Then they will both be connected to the “common” terminal of the capacitor, but also to the “common” power wire.
I was a little trepidatious to try it because I’m no HVAC guy and, even though I understand electronics, I wasn’t completely convinced I knew exactly how the motor was wired internally. There may be some sort of component in there that might be damaged by connecting 115 Volts to the brown and white wire. I couldn’t imagine what would be in there that it could hurt, but you never know what’s inside something that you don’t have a diagram for. I decided to just go with my judgment and how I THOUGHT it would work and give it a shot.
VIOLA! It worked like a champ and the motor is running like a top as we speak.
So, basically, if you’re trying to hook a four wire condenser fan motor into a three wire condenser unit, if yours is set up like mine and the “common” power wire is also connected to the “common” terminal on the capacitor, you simply connect both the white “common” power wire and the brown and white “common” capacitor wire from the new fan motor to the “common” power wire in the unit.
If you don’t have a wiring diagram of your unit, or you can’t figure out whether your system is wired similarly to mine, the alternative is to buy a single capacitor for the fan motor, hook the brown and brown and white capacitor wires from the new fan motor to it. Secure it inside the unit somewhere where the contacts won’t short out and the whirling fan blades won’t hit it (zip ties are your friend), then connect the black and white power wires from the fan motor to the existing power wires in the unit, and leave the “fan” side of the old dual capacitor disconnected.
I’m sure I overexplained as usual and made this much longer than it needed to be. I just hope it helps make someone’s life a little easier than mine was over the past few days trying to figure out what to order and then how to connect it when it got here.
If you found this post helpful, please leave a comment so I can get a nice warm fuzzy feeling.