Condenser Fan Cycle switch question

[LightGuy48]

We recently had a Copeland scroll compressor fail in a commercial unit at a broadcast transmitter site that needs cooling almost year around due to the heat load. Both units at the site have fan cycle switches on the condensers due to the low outdoor temps we receive in the winter.

The technician that came out to replace the unit believes the failure was caused because he says the fan cycle switch was no longer working, which is possible.

However, the thing that got me is he said because the unit uses a scroll compressor instead of conventional compressor a fan cycle switch is not required. :confused:

I have at least another 1/2 dozen commercial units that came with factory installed fan cycle switches and some with variable speed controls on the condenser fans and everyone of them has a Copeland scroll in it, I've been looking all morning to find a definitive answer to this question but can't find one, can someone help me with this?

I need to know whether to get the guy back out to finish the job or maybe I need to find someone else to finish it.

Thanks

[pecmsg]

All condensing units need some type of head pressure control during low ambient operation, fan cycling is just one.

Posting the Make & Model # of the unit would be a big help. Copeland only made the compressor not the unit.

In the mean time I’d look for another tech.

[LightGuy48]

Having overseen the maintenance of HVAC equipment for almost 20 years I thought this guy was incorrect, but I could tell he was was very much convinced of what he was telling me so that's why I asked the question. Prior to this guy I had always been told to specify fan cycle switches on new system purchases due to the units likely running during winter months but never did someone tell me that if the unit employed a Scroll compressor that some kind of fan control was not needed.

The unit is a Goodman 5 ton unit, split system, I thought I had the model number with me but I don't.

[wildtech]

Agree all units need a fan cycle control of some sort. But I would give the guy benifit of doubt he might be a A/C guy thats pretty good but all hes seen is resd units without low ambient controls, one thing about hvac/r is that its a diverse field and theres no way that every tech can know everything. Also in my opinion the comp should have a crankcase, I know some people think they don't need one, but I'm a fan of them, maybe thats what the guy was refering to. If I remember right I read somewere that all comp scroll como over 6 hp should have crankcase heaters.

[BKS60]

When your next tech comes out you might ask about a free cooling option to go along with a head pressure control.

Curious as to the techs explanation as to why you would not need a pressure control on a scroll?

[LightGuy48]

Most of our units have heaters on them, I never really got any explanation out of the guy as to the basis of his belief that no switch was needed other than Scrolls didn't need them and the only thing necessary for cold weather operation was a heater.

[maxpower]

When your "next" guy comes out,have him install the modulating type of controller. ICM makes a good one. Switches wear out and their not consistant enough for head pressure/temp. control. Just my opinion.

[LightGuy48]

Are they better than the Honeywell units? We have a number of Honeywell fan controls on our DataAire units, the triacs they use have a tendancy to fail. We repair them in-house but it's a pain to pull them apart and work on them.

The triac is only a 20amp device in a TO220 case so there's not a lot of heat dissipation so any problem with the fan motor tends to take the triac with it.

Which model of ICM is it? I was looking at the ICM326, it appears it doesn't even need a connection to high side pressure? It just uses a thermister? I kind of like that, less chance of leaks, but is it reliable?

[maxpower]

Next time you go to your supply house,ask them. Then you can choose the one you like. United refrigeration sell's them in my neck of the woods. It is a thermistor. I dont know the m/n of the control. If you do use switches, install them on the neutral side. Good luck!

[pecmsg]

ICM senses the line temperature. I’ve used them on smaller applications.

The Penn P-66 Control operates on pressure and is designed for larger loads.

[maxpower]

I'm guessing these are small "Bard" units...?

[LightGuy48]

We've got a mix of units, some Bard wall mount packages, some Goodman package units, and some Goodman split units

[ascj]

If you do use switches, install them on the neutral side. Good luck!

That sounds like bad advice. The last I checked 120v and 277v are the only voltages with neutral legs. And you don't want any safety switches on your neutral leg. If a switch shorts to ground you want it to blow a fuse or trip a breaker.

[maxpower]

yea, those controls will work good for those apps. Pecmsg is right , the Penn control is best for larger apps.

[maxpower]

That sounds like bad advice. The last I checked 120v and 277v are the only voltages with neutral legs. And you don't want any safety switches on your neutral leg. If a switch shorts to ground you want it to blow a fuse or trip a breaker.

I'm talking about those small bullet type condenser fan pressure controls switches. They tend to weld theirselves closed when installed on the hot side.

[LightGuy48]

When you say larger applications what do you think the cutoff is? Most of our units are 5 tons or smaller.

Looking at the ICM cutsheet it does list computer rooms as an application, which is along the lines of what we are cooling but they don't get any more specific than that.

Also the ICM is also much cheaper than the P66

[ascj]

I'm talking about those small bullet type condenser fan pressure controls switches. They tend to weld theirselves closed when installed on the hot side.

Maybe I'm missing something, but you "Hot Side" and neutral leg should have the same amp draw. So it should not matter.

As far as welding goes, check manufacture rating before putting your load across it. Most are rated for up to 240v and 6amps.

[pecmsg]

When you say larger applications what do you think the cutoff is? Most of our units are 5 tons or smaller.

Looking at the ICM cutsheet it does list computer rooms as an application, which is along the lines of what we are cooling but they don't get any more specific than that.

Also the ICM is also much cheaper than the P66

Up to 1-Ton refrigeration units the ICM is acceptable. (I always recommend the P-66) For the equipment and space your cooling money shouldn’t enter the equation, go with the Penn-66

[klrogers]

Both the P66 and the ICM can be used with sleeve bearing motors, but for best long term reliability you should make sure the condenser fan motor is a ball bearing type, sleeve bearings do not like running at low speeds.

Kevin

[crab master]

Agreed with most of the statements you've gotten here; however the last transmitter site I worked on they were paranoid about dust. I had to write a sequence that the economizer would only run during the months snow was expected to be on the ground, Nov - April, basically my take was their guys didn't want to change filters. I was at a loss on why they didn't use economizers more than what they did cause they could've saved a lot on the electric bill.
On the fan cycling controls the tech is definitely incorrect with the application you are running in. Scroll/Recip (conventional) compressors in this type of application will need head pressure control. IMO - on aircooled equipment anytime you are running cooling continuously less than 65 deg F outdoor air temp then you need some kind of low ambient/head pressure controls.
I would definitely put in a ball bearing motor and I would go with the P-66 or ICM fan cycling control, whichever can handle the load the best based on motor HP.
A fan cycling control would work as well, but given your conditions it will be cycling quite a bit. I've gone as far as putting in overated contactors for the fan and having the fan cycling simply cycle the low voltage to the contactor and let the contactor take the brunt of the abuse. The other thing I've found is all to often fan cycling controls get set too tight. Let the pressure climb for a bit before the fan kicks on and then make sure it can't run continously less than the min. pressure you want to see. This lengthens your fan run times a lot.

[LightGuy48]

Dust is a huge problem at transmitter sites, the problem is the HV in the transmitters. With 9kV - 12kV DC it attracts the dust which can eventually lead to corona and arc over problems, so outside air has to be well filtered or in the best installations a closed system with no outside air.

Whenever possible if we have to vent outside we try to use positive pressure through a well filtered air intake to supply the make up air for the building. These days there are a lot more solid state transmitters where we can use a closed system but for high power at high effeciency there is no susbstitute for tubes and they need a lot of air and there is a lot of heat to dissipate.

I like the idea of a secondary contactor for the fan, definitely cheaper to replace the contactor than the switch, plus if it's a 2 pole the two contacts could even be paralleled to minimize the amount of pitting and carbon buildup.

[jpsmith1cm]

Next time you go to your supply house,ask them. Then you can choose the one you like. United refrigeration sell's them in my neck of the woods. It is a thermistor. I dont know the m/n of the control. If you do use switches, install them on the neutral side. Good luck!

Why would it matter which side of the line the switch is installed in?

Either side of the line will see the same amperage.

Aso, I agree with Timebuilder in that I was taught to not wire switches into the neutral line because it is possible for the switch to fail or short and cause continuous operation.

[LightGuy48]

I'm kind of confused by the switch comments because there really is no neutral. Unless you're working on a 110v window type unit most of the time the fan windings are from phase to phase so it's going to have 208, 240, or 480v across it, no matter which side you put the switch on your still on a leg with voltage, not a neutral. I can't think of the last time I saw a unit with a neutral, only a safety ground.

Maybe they're saying the 'neutral' leg implying it's the simpler side since it has no capacitor on that side to worry about, but it's not at neutral potential.

[jpsmith1cm]

I'm kind of confused by the switch comments because there really is no neutral. Unless you're working on a 110v window type unit most of the time the fan windings are from phase to phase so it's going to have 208, 240, or 480v across it, no matter which side you put the switch on your still on a leg with voltage, not a neutral. I can't think of the last time I saw a unit with a neutral, only a safety ground.

Maybe they're saying the 'neutral' leg implying it's the simpler side since it has no capacitor on that side to worry about, but it's not at neutral potential.

If it is a 208-240v or a 460v fan you are absolutely correct, there is no neutral side.

Sometimes we get distracted from the point at hand, sorry. :bump:

[LightGuy48]

Certainly no distraction... I enjoy reading the threads on the forum and the occasional OT posts but I am curious about idea that the location of the switch in a circuit could make a difference in the life of the switch.

As another poster commented, no matter which leg is involved it's still carrying the same current. Now obviously short cycling from an incorrectly set adjustable switch, a poorly built fixed switch, or an undersized switch could certainly cause either welded contacts or so much carbon or pitting that the switch doesn't engage at all.

[jpsmith1cm]

I don't exactly understand it, either.

I agree that no matter which side of the circuit the switch is in, hot side or neutral side, it will see the same amperage and cause the same amount of wear on the switch.

Short cycling or an incorrect switch will also be a problem no matter what side of the circuit it is in.

[superfittertech]

ICM senses the line temperature. I’ve used them on smaller applications.

The Penn P-66 Control operates on pressure and is designed for larger loads.

p-66 needs a high temp ball bearing motor ($$$$)

[Airmechanical]

first of all you need to set a high differential on the fan cycler

then, if you have problems burning up the contacts

have the fan controller operate a relay that controls the motor



.

[tombeaux]

Agreed with most of the statements you've gotten here; however the last transmitter site I worked on they were paranoid about dust. I had to write a sequence that the economizer would only run during the months snow was expected to be on the ground, Nov - April, basically my take was their guys didn't want to change filters. I was at a loss on why they didn't use economizers more than what they did cause they could've saved a lot on the electric bill.
On the fan cycling controls the tech is definitely incorrect with the application you are running in. Scroll/Recip (conventional) compressors in this type of application will need head pressure control. IMO - on aircooled equipment anytime you are running cooling continuously less than 65 deg F outdoor air temp then you need some kind of low ambient/head pressure controls.
I would definitely put in a ball bearing motor and I would go with the P-66 or ICM fan cycling control, whichever can handle the load the best based on motor HP.
A fan cycling control would work as well, but given your conditions it will be cycling quite a bit. I've gone as far as putting in overated contactors for the fan and having the fan cycling simply cycle the low voltage to the contactor and let the contactor take the brunt of the abuse. The other thing I've found is all to often fan cycling controls get set too tight. Let the pressure climb for a bit before the fan kicks on and then make sure it can't run continously less than the min. pressure you want to see. This lengthens your fan run times a lot.

I agree . on R22 systems we've set the penns to CI at 325 psi and CO at 225 and closely watched the suction pressure as to keep it from dropping below a 64 psi while in an on cycle as a base guideline. We set the penns to control the condenser fan relay / contactor control voltage exclusively.No problems to date as a result other than " good office samaritons occasionally reporting the units are short cycling". Yes ,you read it right .Good luck .:patriot:

[williams2111]

Get a hoffman control that you can start the motor and run a more constant head rather than racing it up and letting it fall through the floor. Ball bearing motor is a must for the low rpm setups.

[guy597]

A Carrier Motor Master is also a way of going depends how critical the application is. A ball bearing motor is also needed with it.

[Gleng]

Scroll or recip,is not the issue.Expansion valves do not operate properly with low head pressure and flash gas. Systems need proper head pressure and proper charge to operate properly whether they are reciprocating or scroll.

[richper]

controling head pressure is just part of the solution.In this situation I would also install a crank case heater and install pump down and posibly a hot gas bypass valve to insure compressor longevity.We have alot of jobs like yours with the same type of equipment that we modified with all the above and once we sold the customer on this initial investment, they claim thier compressor replacemens are way less then before.

[CommtechinVA]

When your "next" guy comes out,have him install the modulating type of controller. ICM makes a good one. Switches wear out and their not consistant enough for head pressure/temp. control. Just my opinion.

X2:yes::yes:

[Airmechanical]

I agree . on R22 systems we've set the penns to CI at 325 psi and CO at 225 and closely watched the suction pressure as to keep it from dropping below a 64 psi while in an on cycle as a base guideline. We set the penns to control the condenser fan relay / contactor control voltage exclusively.No problems to date as a result other than " good office samaritons occasionally reporting the units are short cycling". Yes ,you read it right .Good luck .:patriot:


i worry about overheating the compressor and oil at 300 psi and above

i like to max my head pressure controllers out at 295

i keep about a 75 psi differential

with those settings, the suction pressure drops to around 60 psi for a short duration, it's not gonna freeze

also we don't let our computer rooms go under 70 degrees

"somehow" the IT guys listen to us on that subject



.

[crab master]

Work in a -10 deg F day, you'll change your mind. Granted where you don't see the temperature swings as drastic you won't have to set it as far apart, but when your freezing up units because someone set the differential too low and the cut out at 200 (cut in at 250) and you watch your head pressure drop to 150 before it starts to climb...
Not only that but just because you set it at 325 doesn't mean it's going to run there very long at all, especially on cooler days. Many 105 - 115 deg days where it does run that pressure most all day long and units still running for years. Units in my house - knock on wood, are 12 years old and they seen many days running over 300 psig.

[Airmechanical]

Work in a -10 deg F day, you'll change your mind

your right, at 10 below i would not worry about compressors overheating


.

[brooklyntech]

All good points about the P66 controller and associated head pressure controls. You can go for cheap-fan cycling control to expensive-put a drive on the condeser fan (also replace the motor with a drive compatible motor). As far as the switch on the neutral side, I ve been taught never on neutral of 115volt circuit. On 208/230volt there is no neutral as you stated, thats just expression. Back to the original thread at hand, you stated that the mechanic said no fan cycling control needed. This might be true- depending on your condensing unit. Do you have a liquid receiver? How about a head master valve? If you have that stuff you can run a condenser fan balls to the wall, while ur liquid gets fed to your txv at almost a constant temp/pressure. I believe that is how Liebert does that. Also that is how we set up our refrigeration condensing units to operate in the winter time.

[ESokoloff]

I'm kind of confused by the switch comments because there really is no neutral. Unless you're working on a 110v window type unit most of the time the fan windings are from phase to phase so it's going to have 208, 240, or 480v across it, no matter which side you put the switch on your still on a leg with voltage, not a neutral. I can't think of the last time I saw a unit with a neutral, only a safety ground.

Maybe they're saying the 'neutral' leg implying it's the simpler side since it has no capacitor on that side to worry about, but it's not at neutral potential.


Just for clarification as stated earlier, 277 has one hot & one neutral leg.



Also wind influence (passing objectionable air past the condenser coil) should be considered/addressed when/where a factor of head pressure control.

[Airmechanical]

Just for clarification as stated earlier, 277 has one hot & one neutral leg.


yes, you are correct, about a 277 volt "single phase" circuit



.

[LightGuy48]

Back to the original thread at hand, you stated that the mechanic said no fan cycling control needed. This might be true- depending on your condensing unit. Do you have a liquid receiver? How about a head master valve? If you have that stuff you can run a condenser fan balls to the wall, while ur liquid gets fed to your txv at almost a constant temp/pressure. I believe that is how Liebert does that. Also that is how we set up our refrigeration condensing units to operate in the winter time.

I'll have to check on the liquid receiver I don't remember, there is a TXV at the evap coil.

Thanks

[LightGuy48]

yes, you are correct, about a 277 volt "single phase" circuit

True, but as an example all of our Liebert and DataAire units which are 277/480 all have 480v motors. There is no neutral in the unit in our installations.

[Airmechanical]

True, but as an example all of our Liebert and DataAire units which are 277/480 all have 480v motors. There is no neutral in the unit in our installations.

the only way 277 volts will operate a 277 volt component, is with a neutral



.

[crab master]

Back to the original thread at hand, you stated that the mechanic said no fan cycling control needed. This might be true- depending on your condensing unit. Do you have a liquid receiver? How about a head master valve? If you have that stuff you can run a condenser fan balls to the wall, while ur liquid gets fed to your txv at almost a constant temp/pressure. I believe that is how Liebert does that. Also that is how we set up our refrigeration condensing units to operate in the winter time.

Excellent points and good catch.


However, the thing that got me is he said because the unit uses a scroll compressor instead of conventional compressor a fan cycle switch is not required. :confused:

As previously posted though head pressure control has nothing to do with conventional or scroll compressor, but if he has a head master valve, that's another story. I am glad you brought that up though.

[Tommy1010]

Theres some great info on fan cycling control here. I need to install'em on a bunch of our units here at mill which almost all run yr round. The only reason i can imagine the tech stating scrolls dont need'em (which I dont agree with) Is just because scrolls are LITTLE more tolerant to liquid. But tolerant doesnt mean you WANT it to happen. Im toerant of my 6 yr olds temper and attitude, but that dont mean I approve of it. lol

[drunkenkoala]

I had the same problem with a unit our salesmen sold that was meant to use for resi application, but he sold it has a server equipment.. After 2, -35 winters, and 2 failed compressors, we realized that the icm( fan cylcing control ),and crank case heater wouldn't cut it. We eventually had to had head master controls, we also added accumulators on there to as we were getting bad liquid slugs during the very very cold days..
As far as Scrolls, we do alot of computer rooms that need to run low temp, I have found that scrolls definatly all need some method of head pressure control, and a Crankcase is also a cheap way to prevent flooded starts on those cold days.