Condenser Fan Motor Swap?

[RonRock]

My HVAC is starting to show it's age. I plan/hope to make it through till next spring to replace the whole system.

So last week the condenser fan motor went out. The unit is a 20 year old York 3.5 ton. 12 seer. It had a 2 speed motor that I'm sure had to do with the efficiency of the unit. But efficiency is long gone and low priority. So I look for a replacement motor. BTY we are in mid 90's with 100's in the next few days forecast.

So the OEM type replacement is $250 and 3-4 day wait for shipping, not available local. The York dealer will special order, but it will take time for shipping. So I found a replacement motor. The high speed on the OEM was 850 RPM. The replacement is 825RPM. Close enough I figure. So I bought and installed it. AC is working again. $100 and a couple days in a hot house, no big deal.

Long lead up to the question, sorry I thought that info might be pertinent.

In my research I found that readily available motors often have a speed of 1025 RPM or so. I almost went with that figuring that the higher speed might help pull the heat away a bit better. I was concerned about the fan blade balance at a higher speed.

Is it common practice to use a faster condenser fan motor as a replacement? Would I gain anything with a higher speed fan motor? Was I right in my concern about the balance?

Part of the story is that the condenser has been beaten by hail more than once. I am afraid to comb the coil for fear that I will create a leak. I know it's hard on the system, but it's working. I'll probably leave it alone.

I should put the gauges on it, but don't know what to expect to see with the beaten condenser coil. As far as I can recall the gauges have not been on the system since install.

 

[EOC_Jason]

As long as it is the same HP motor and the RPM is close you should be good. I don't know what the effect of putting a higher RPM in would be, it would *probably* be okay as a temp fix, but I wouldn't want to do it long-term. I can only guess it would create more negative pressure inside the unit if there is an air-flow restriction, otherwise anything to bring the freon temp down will probably pick up a very small amount of efficiency.

You should be okay to straighten out the fins if you take your time and do it carefully. The fins are slid on the coils, they aren't soldered or anything like that. I would use a small blade screwdriver and take your time. Don't use the comb trying to straighten out several rows at a time, that might get you in trouble. Don't try to make it 100% perfect, just get the big areas so air can flow through.

I wouldn't put gauges on it if you don't feel confident or have spare refrigerant. Likely a valve will stick open some when you remove the gauges and you'll lose some refrigerant trying to get it to close, and even then might end up with a slow leak. Just leave that alone if it's cooling fine.

 

[MagKarl]

Be aware that it takes more power to run a fan faster and it's non-linear, you would pull more amps.

 

[TRWham]

Yes, fan power will increase with the cube of the ratio of speed, so a 1025 rpm fan will draw almost 80% more power than the same fan at 850 rpm. The change in flow is linear, so you'll get 20% more air flow.

 

[American Locomotive]

More condenser air flow is not always better. It will have been a carefully designed and matched system.

Combing the coil will not cause a leak, unless you're doing it with a steel gravel rake.

 

[66cj225]

I'd go inside and enjoy the cool air. Maybe check to be sure the fridge is still running. Save the worrying for a cool day. You'll regret creating a leak in ways not yet imagined.

 

[RonRock]

Thanks guys, all good thoughts.

Sounds like I made a safe decision and will stick with it.

I am surprised that more condenser airflow is not always better. At least to a reasonable point. Especially concerning that my condenser is well beaten.

I'll take anther at combing the fins after this crazy heat wave passes.


One unexpected problem with building a new house. All that it includes is the same age. It's all starting to show that age. Hopefully we can spread it out this time.

 

[Fixin'Stuff]

I am surprised that more condenser airflow is not always better. At least to a reasonable point.

In the constant search for energy savings, the engineers have most likely figured out exactly the point at which more is not better, and just burns more electricity with no return for the added expense. Some of the newer units have huge condensers and fans that turn so slowly that you can barely hear them running.

 

[PFSard]

One unexpected problem with building a new house. All that it includes is the same age. It's all starting to show that age. Hopefully we can spread it out this time.

Curious : What other systems/devices etc from your build are starting to cause problems, necessitating replacement?

 

[EOC_Jason]

I am surprised that more condenser airflow is not always better. At least to a reasonable point. Especially concerning that my condenser is well beaten.

Like someone else said with the motor usage, your power consumption goes way up compared to the CFM increase. Plus it adds more noise which nobody wants. It's more efficient for them to use a larger coil (for more surface area to cool)...

 

[LS6 Tommy]

Don't forget, moving too much air across the condenser can cause the refrigerant to overcondense. This can cause condenser flooding and efficiency goes down until the liquid boils off again.

Tommy

 

[RonRock]

Curious : What other systems/devices etc from your build are starting to cause problems, necessitating replacement?

Last winter the frost heave destroyed our pool. Not a huge deal, it was 18 years old above ground. This year we replaced it. While filling the pool the well pump went out. It was a 1995 when the house was built. Again no surprise, but not cheap. The pump motor had apparently swollen up and got stuck in the casing and broke off the pump when they were pulling it. The pump replacement was on short order and he was busy. No time to deal with the motor stuck. He will have to return and pull the new pump to force the old motor down in the casing deeper. Then extend the pipe so that the new pump will go down farther. So a couple grand for the pump, another for the return visit for the finish work. On top of the pool expense.

It has been obvious that the HVAC system is in need of replacement for a year or so.

The JennAir built in fridge lost it's compressor a couple years ago. Whirlpool built in oven has lost it's system board a couple times, it's now obsolete. The garbage disposer bottom went out causing water damage to the wood floor.

Typical home owner experience. But this house was built in 95 and everything is the same age. I did my best to buy quality when we built, but still.

 

[RonRock]

Like someone else said with the motor usage, your power consumption goes way up compared to the CFM increase. Plus it adds more noise which nobody wants. It's more efficient for them to use a larger coil (for more surface area to cool)...

The York condenser does have a large coil and with the 850 RPM motor fairly quiet. Good points.

 

[eddieK]

As long as it is the same HP motor and the RPM is close you should be good. I don't know what the effect of putting a higher RPM in would be, it would *probably* be okay as a temp fix, but I wouldn't want to do it long-term. I can only guess it would create more negative pressure inside the unit if there is an air-flow restriction, otherwise anything to bring the freon temp down will probably pick up a very small amount of efficiency.

You should be okay to straighten out the fins if you take your time and do it carefully. The fins are slid on the coils, they aren't soldered or anything like that. I would use a small blade screwdriver and take your time. Don't use the comb trying to straighten out several rows at a time, that might get you in trouble. Don't try to make it 100% perfect, just get the big areas so air can flow through.

I wouldn't put gauges on it if you don't feel confident or have spare refrigerant. Likely a valve will stick open some when you remove the gauges and you'll lose some refrigerant trying to get it to close, and even then might end up with a slow leak. Just leave that alone if it's cooling fine.

Use a stiff wire brush...fin comb is about impossible.

The fan speed was calculated to create the proper latent heat transfer....altering this alters the heat transfer along with amp draw.

Latent heat is the process of a liquid turning to vapor and vise versa...latent heat is the energy released or aborbed when a substance changes state. The condensing unit condenses the hot gas from the compressor into a hot liquid and sends it to the evaporator to evaporate and extract heat. If you alter the heat transfer from its original design, you alter the process that helps remove (transfer) this heat. What you don't want is that liquid to back up into the compressor...nor do you want not enough liquid to travel to the expansion device.

Either of these results can cost you ALOT more than an expensive fan.

That fan was two speed for a reason, with low ambient temps it allows more heat transfer on low fan speed.

 

[Bretny]

You can possibly see how more cfm would effect the system by taking your garden hose and spraying the condensor. Its will basicly pull more heat out of the system but i wouldnt bother. How ever they do make a condensor misting system to spray water on the coil when the can come on.

Filling a pool with a well is a prety bad idea. If you do it its best to do it over about 2 weeks and only have the hose trickle in.

 

[bonneyman]

Yeah, keep the RPM of the new motor close to the OEM.

Many older Carrier's used 1100 RPM motors. Try finding a 208-230v motor with 1100 RPMs! It was a marketing ploy that Carrier had GE do in marking their motors, so unsuspecting techs would buy OEM replacements so as to "match" the speed. If I see a motor marked 1050-1100 I put in a standard 1075. Just make sure the amp draw is close or slightly less than the original motor and you'll be fine.

The RPM's are a result of the number of poles the motor has. 825 RPM models are 8 poles - more expensive to make but typically have lower running amps than 6 pole motors of the same HP. Therefore, you find them on higher efficiency equipment, as the lower amp draw helps in raising the SEER rating. But, it costs more to replace when it goes bad.

Here's a link to literature with everything you'd ever want to know about motors:
http://www.fasco.com/distribution/fasco-motor-facts/fasco-facs-english/

 

[RonRock]

Here's a link to literature with everything you'd ever want to know about motors:
http://www.fasco.com/distribution/fasco-motor-facts/fasco-facs-english/

Good information.