Head pressure controller - 2 speed fan

ChrisJ

Hi all,
Just want someone to double check me on this.

My outdoor unit uses a simple 2 speed fan motor and I'm really considering installing a head pressure controller. Something like the ICM ICM325. Just something I'm mulling over. Ran the unit in test mode this morning when it was 57F out and I'm betting it was underfeeding. Probably still acceptable, but pushing it.

On this setup, my guess is I'm going to only use high speed on the fan and allow the controller to do the rest. The problem being, the PCB switches between high and low. From the schematic, it appears high and low (relays K3 and K4) can simply be connected together and then feed the controller.

Thoughts?




The other issue is going to be where to put the controller. I highly doubt I have enough room under the cover on the condensing unit.

ratio

It's not uncommon to make a "Y" connector with Stakons for this purpose, or you could just wire nut them together.

Keep in mind that I only think this will work, I've never actually done it, so let me know how it works out, please.

JUGHNE

How about just getting power from the compressor C terminal on the contactor. (Just like old school common AC). Usually a lot of empty spades there. That would be your 240 VAC there to the control.
That would leave K3 and K4 intact, with no connections on output.
It would look untouched in the event of warranty return.
Low speed lead insulated of course.

That 325 control would probably fit inside a common AC pull out power disconnect mounted on the outside of the ACU.
Just take the guts out, use the back KO's and it would look proper.
Plus, you can just lift the lid to adjust, tinker, and monitor the LED's.
We know you will. ....don't have to open ACU then.

The back of the 325 appears to be a flat plate heat sink BTW.

Is the E21 connection to the CS coil the hi/low control?
It is a hot gas bypass of sorts?

ChrisJ

JUGHNE said:

How about just getting power from the compressor C terminal on the contactor. (Just like old school common AC). Usually a lot of empty spades there. That would be your 240 VAC there to the control.
That would leave K3 and K4 intact, with no connections on output.
It would look untouched in the event of warranty return.
Low speed lead insulated of course.

That 325 control would probably fit inside a common AC pull out power disconnect mounted on the outside of the ACU.
Just take the guts out, use the back KO's and it would look proper.
Plus, you can just lift the lid to adjust, tinker, and monitor the LED's.
We know you will. ....don't have to open ACU then.

The back of the 325 appears to be a flat plate heat sink BTW.

Is the E21 connection to the CS coil the hi/low control?
It is a hot gas bypass of sorts?

Hi @JUGHNE thanks for commenting.

The contactor is a PCB mounted sealed contractor. So I think that idea is out the window.

The fan connection I think is 0.250" quick connects, but I could be wrong. I'm sure I can find a way to use the fan relays without modifying anything terrible, certainly not the PCB.

E21 controls the solenoid on the compressor to unload part of the scroll. Energized it forces it into "high stage". It always starts unloaded, and goes into low stage first. I think this is why the hard start kit was causing a bang on startup, just too much power in such a state I guess. Odd Copeland says it's ok but I like it starting slower and easier.

https://youtu.be/gRfF_z-_eNM

JUGHNE

So if the K2 compressor contact fails then a new PCB would be needed?
And are the fan relays just simple electro-mechanical mini PCB mounted items?
I might have a 2 stage AC job next spring that needs the control also.

ChrisJ

JUGHNE said:

So if the K2 compressor contact fails then a new PCB would be needed?
And are the fan relays just simple electro-mechanical mini PCB mounted items?
I might have a 2 stage AC job next spring that needs the control also.

Normally I'm going to say yes, they would want you to buy a new board. For me, no, I'd solder on a new contactor. They claim (they being Emerson) the sealed contactor lasts a lot longer as the contacts don't oxidize.

The fan relays are just normal mechanical relays as you said. Typical small rectangular black boxes, though I forget the brand.

ChrisJ

@JUGHNE May be a stupid question but how do guys usually determine if a controller is necessary. Just by what conditions a unit will be used under, or do they tend to wait until a problem shows up, I.E. icing up?

That's why I'm kind of on the fence. I suspect my system would benefit from it, but not totally sure it's necessary. Even if the evap is being underfed a little when it's in the 50s out, will it even matter with short run times?

JUGHNE

The outside temp and length of needing to run at low amb.

I put them on the 3 ACU for our movie theater, as it is a volunteer run enterprise and you might find 1 system in heat mode and 1 in AC mode. Plus with a full house of 67 you run AC in low amb.

Comm kitchens where they might run almost year around.
Flower shop where owner likes to leave temp set at 68 overnight.

There a lot of opinions on the exact temp numbers.
Some go with 55 or below.....it is one of those "just depends" answers.

ChrisJ

JUGHNE said:

The outside temp and length of needing to run at low amb.

I put them on the 3 ACU for our movie theater, as it is a volunteer run enterprise and you might find 1 system in heat mode and 1 in AC mode. Plus with a full house of 67 you run AC in low amb.

Comm kitchens where they might run almost year around.
Flower shop where owner likes to leave temp set at 68 overnight.

There a lot of opinions on the exact temp numbers.
Some go with 55 or below.....it is one of those "just depends" answers.

So ultimately, if the system is working and not complaining I don't have to do anything.

EBEBRATT-Ed

as long as the compressor is not flooding back, coil icing superheat maintained

ChrisJ

Actually.

My test from this morning must be flawed. Perhaps it just didn't run long enough.

I say this, because it was in low stage and that TXV should be plenty for 2 tons, even 2.5 tons even at such a low ambient. Using 40 PSI drop for distributor, 65F condenser temp, 60F liquid temp that valve will flow just enough for 2.5 tons. I know my 3 ton system isn't doing over that in low stage. I didn't measure anything, but I doubt that condenser is running below 65F with a 57F ambient.

Test must be repeated and for a much longer time I guess.

ChrisJ

@JUGHNE @EBEBRATT-Ed

Is there any downside to running a controller like this with a sleeve bearing fan? I.E. what's the reason Goodman used an ECM fan on the better model vs mine instead of just using this fan with a controller?

I'm eyeing up the ICM325HN and it will fit under the cover.......barely. Luckily I took the hard start out because it was causing banging on startup so that room is freed up.

ChrisJ

I ordered the controller so it should be here Monday.

Also ordered a 40W CCH I hope will fit this small diameter compressor (5.5").

After researching it the best I could, it seems like the best idea for me. Especially with how often we have hot days that drop into the low 60s, even low 50s at night and the house stays hot.


Besides.
It'll also ensure that 3 ton TXV is never too small.

ChrisJ

Ok.

Need some opinions!

Here's what I see being the options.


Original circuit. The relays are on the PCB and are controlled by the board. Low and High do nothing more than switch with low and high stage. I got this by looking at the traces on the PCB. The wire on the fan molex actually plugs right back into the same PCB right by the sealed contactor. Not sure if it's switched or not at this point.









Option A. I kind of like this as it's simple, and would still keep low and high speeds in use vs the stage the unit is in. Don't know if the controller will care about it switching speeds while running, but I suspect not?




Option B, ditch low speed. This is what ICM suggested doing though I suspect it's because they don't know what's going on with the PCB and wanted to be safe.




Option C, ditch switching too. Not sure how the ICM325 would like this? It appears to have a 24VAC in from thermostat, so I donno.






Thoughts?

ratio

Is that an ECM motor, with 24v going to it in addition to the line voltage?

I'd do as mentioned above, come off the contactor, through the speed control, & to the fan. I don't know how happy the motor would be running at reduced speed in low gear. It's my understanding that multi-speed PSC motors (not ECM) are mainly multi-horsepower, not multi-speed; they merely slip more in lower gears. I'd expect the speed control to simply control to a lower speed when the compressor is running in low gear. The condenser would be operating at a lower ∆T, so the fan could slow down more to keep it's sensor in the desired range.

ChrisJ

ratio said:

Is that an ECM motor, with 24v going to it in addition to the line voltage?

I'd do as mentioned above, come off the contactor, through the speed control, & to the fan. I don't know how happy the motor would be running at reduced speed in low gear. It's my understanding that multi-speed PSC motors (not ECM) are mainly multi-horsepower, not multi-speed; they merely slip more in lower gears. I'd expect the speed control to simply control to a lower speed when the compressor is running in low gear. The condenser would be operating at a lower ∆T, so the fan could slow down more to keep it's sensor in the desired range.

Nope, just a PSC, no 24VAC to the stock fan.
Though the 18 SEER unit does use an ECM of sorts, and the same relay hookup, only the L2 goes direct to the motor and then I guess low voltage is feed to the relays.


I'm thinking I should just pull Goodman's fan out and install a decent ball bearing fan with a class F insulation to deal with the extra heat. Something like this.

Century model FE1018SF
Ball bearing, 825 RPM single speed. Class F insulation and rated to 70C ambient.





Problem is, it seems no one wants to say it's ok to use their motor with a Triac style controller like ICM's but I'm betting that ball bearing motor has a pretty good chance with dealing with it. Much better than Goodman's no name, no information sleeve bearing motor.

What do you think? Worth the investment? I'd probably use the option C drawing I posted above with it.

Harvey Ramer

Just go full bore and spend some moldy money! A 3-phase motor driven from a VFD with a pressure transducer.

#nailed-it

Matt_67

@Harvey - we actually do that quite a bit on industrial air conditioners we service. Its very reliable and isn't crazy expensive.

On the solid state P66 type controllers we have had decent success with the Century Heatmaster Ultra motors - we have several of them that I think are about 2 years in service now.

ratio

I'd just run with the sleeve bearing motor, switched from the contactor, for now. The sleeve bearing settings on the controller should Just Work, but I think you should be able to turn down the min speed until you're at max amps without issue. (Leave the sensor hanging to force the fan to low, it's looking for about 100° IIRC) I'd leave the hard start knob in the sleeve bearing range. No harm in ordering the motor, but not much reason to change it out, you aren't going to get a credit for the old one, just run it 'til it fails.

ChrisJ

Matt said:

@Harvey - we actually do that quite a bit on industrial air conditioners we service. Its very reliable and isn't crazy expensive.

On the solid state P66 type controllers we have had decent success with the Century Heatmaster Ultra motors - we have several of them that I think are about 2 years in service now.

I wanted to go with a Heatmaster Ultra but it looks like they stopped making them. Also, the smallest which is 1/4HP gives me height concerns.

So, I had to go with a Heatmaster 70C model.




@ratio I partially agree, except that I don't want to deal with a failure if I can avoid it. You know how things fail and it's never when it's convenient.


I'm hoping that 70C motor will hold up. The Heatmaster Ultra 80C motors specifically said they were controllable. These do not. What does have me hopeful is it appears the 80C Ultra's had F rated insulation, the same as the 70C model.

Either way, that's got to be a far better motor than the Chinese sleeve bearing one that came with it. No?

@Harvey Ramer Can I throw in hot gas reheat while I'm at it?

ChrisJ

ratio said:

Is that an ECM motor, with 24v going to it in addition to the line voltage?

I'd do as mentioned above, come off the contactor, through the speed control, & to the fan. I don't know how happy the motor would be running at reduced speed in low gear. It's my understanding that multi-speed PSC motors (not ECM) are mainly multi-horsepower, not multi-speed; they merely slip more in lower gears. I'd expect the speed control to simply control to a lower speed when the compressor is running in low gear. The condenser would be operating at a lower ∆T, so the fan could slow down more to keep it's sensor in the desired range.

I forgot to mention, this appears to be completely correct.
Apparently the low speed winding, is actually a transformer that drops the voltage. There's no benefit to running slow speed in addition to a controller.

ChrisJ

I've got an odd question.

If you drop your evap fan speed normally the evap gets colder.

What happens when you have a fan controller on the condenser fan, and that fan speed drops too?

hvacfreak2

Harvey Ramer said:

Just go full bore and spend some moldy money! A 3-phase motor driven from a VFD with a pressure transducer.

#nailed-it

I have been seeing a lot of exhaust fans with this arrangement lately. The power supply is single phase going into a small Yaskawa VLT 1000 drive used as a converter to a 3 phase motor.

HVACNUT

@ChrisJ
A/C season is just about over Chris.
To be continued?

BTW, I spoke to my service manager. He doesn't remember any equipment coming through with a 6 ton TXV. He brought it up on the computer. It only shows 1.5-3 and 3-5.
When I go back I'll ask the lead installer.

ChrisJ

HVACNUT said:

@ChrisJ

A/C season is just about over Chris.

To be continued?



BTW, I spoke to my service manager. He doesn't remember any equipment coming through with a 6 ton TXV. He brought it up on the computer. It only shows 1.5-3 and 3-5.

When I go back I'll ask the lead installer.

You have to remember, this is on their high seer air handlers, not the standard 13 seer nominal ones.


A/C season is almost over, yep.

But I'm hoping to install the fan controller, CCH and AO Smith / Century 70C ball bearing motor this weekend. We'll see what happens.

The default config for the CCH is to have a bi-metal switch on the exhaust line from the compressor that closes in the mid 60s and opens in the mid 70s I believe. I'm still on the fence if I want that, or if I want the heater running whenever the compressor isn't. I know that way is safer, but I don't know if it even matters and if it's worth the extra power all summer long.

I suspect the OEM way is fine since they use it on their heatpumps.

ChrisJ

Correction

Looks like the switch turns on at 67F, off at 85F.

JUGHNE

I am sure you know about the self regulating CCH....just like heat tapes. Inverse heat output to amb temp. I know you know the term for it.

ChrisJ

JUGHNE said:

I am sure you know about the self regulating CCH....just like heat tapes. Inverse heat output to amb temp. I know you know the term for it.

Yeah I saw a few, but I couldn't find any actual real specs on them other than "60W @ 0F" Ok, what's it at 40F? 50F? 60F? That and they all seemed to be insanely long.

ChrisJ

It's done.
ICM325 + Century ball bearing 70C ambient motor and a 40W crankcase heater.

https://youtu.be/qRMD3zoxtrg


The start up sound is much worse in the video than in real life. The sound is similar, but the volume is screwy. At 1:33 in the video you hear a car revving that was on the other side of our block for a good volume reference. This is unrealistically quiet now when it's cool out. I've never heard a unit near this quiet.

The main thing you hear is the fan motor complaining about the speed.

This is very weird to me, because it was 56 degrees out and I had warm air blowing out of the unit. I have it adjusted for around 250 PSI when it was 65 outside.





The best part? Absolutely no modifications were done to the hardware it self aside from 2 small screw holes for the controller. No cut factory wires, no holes drilled for the new fan motor.

The factory ON\OFF relay for the fan is in use but the HIGH\LOW relay is bypassed by a connection supplied by them on the PCB.

ratio

That's great. The warm air is startling, but an indication that it's working properly.

ChrisJ

So

I can't wrap my head around this. I keep trying, but there's too many variables.

The condenser fan's speed is determined by head pressure. So, the lower the load, and or the cooler the air outside, the slower the speed. Right?


Here's what's confusing me.

What happens when I slow my evaporator fan down? Does that also cause the outdoor fan to slow down? If so, am I still running the evaporator colder, therefore pulling more humidity out (I assume yes)?

I'm going to assume the evaporator temperature is pretty independent of what the condenser fan is doing. The outdoor fan is controlling my head pressure to keep the TXV satisfied and to keep the refrigerant from backing up in the condenser, and as long as that pressure is within range, nothing changes. The TXV is controlling the evaporator based on load (really, superheat) and therefore slowing the evaporator fan down, means the evaporator must get colder for the same conditions regardless of what's going on outside.

I think?

hvacfreak2

ChrisJ said:

So

I can't wrap my head around this. I keep trying, but there's too many variables.

The condenser fan's speed is determined by head pressure. So, the lower the load, and or the cooler the air outside, the slower the speed. Right?


Here's what's confusing me.

What happens when I slow my evaporator fan down? Does that also cause the outdoor fan to slow down? If so, am I still running the evaporator colder, therefore pulling more humidity out (I assume yes)?

I'm going to assume the evaporator temperature is pretty independent of what the condenser fan is doing. The outdoor fan is controlling my head pressure to keep the TXV satisfied and to keep the refrigerant from backing up in the condenser, and as long as that pressure is within range, nothing changes. The TXV is controlling the evaporator based on load (really, superheat) and therefore slowing the evaporator fan down, means the evaporator must get colder for the same conditions regardless of what's going on outside.

I think?

I would think that the condenser fan speed controller is actually reducing the capacity of the condenser coil since it is designed for a much higher ambient and would be way over sized in lower ambient temperatures at full design air flow. And I would say no to the evaporator fan speed question , at least in regards to air conditioning applications. When the evaporator fan speed is reduced the temperature split still exists so the load has not been reduced .

JUGHNE

Single stage AC/single speed fans are used with VS blowers. They can be set up to run at reduced fan speed for the first part of the cooling cycling. These have no temp sensor in the air stream. It is just your best guess (Spockism) to set low/high speeds to prevent freeze up.
If my logic is right (always questionable) I think the TXV only wants solid liquid sent to it, it doesn't know what is going on outside. Your low ambient fan control just assures that the gas is condensing into liquid to be sent to the TXV.

Does your evap have temp sensors that will indicate near freeze up and ramp up the indoor fan?

And then here is another twist in the mix. Even with low AC stage you have much more cond surface than high stage. This doesn't change with hi/lo compressor capacity. Now you have less fan CFM with oversized AC coil on low AC. Hummmm.

Something to think about....and perhaps something to ponder.

HVACNUT

@ChrisJ . You're like a mad scientist with that thing.

ChrisJ

HVACNUT said:

@ChrisJ . You're like a mad scientist with that thing.

If the steam boiler is an example, it'll slow down after a few years when I run out of ideas.

My RH indoors is fantastic, the house is comfortable and the system is happy even running at 51 degrees outside. So far, I'm liking it.

I think anything else I can really do, is just not realistic. Such as hot gas reheat. I'd rather an ECM condenser fan controlled by head pressure, but that's probably not feasible. This winter I have a ton of stuff to finish in the attic. Finish insulating the return duct, fix the supports on the air handler, make a baffle to catch water that's making it into the blower compartment under high latent loads. Make my wiring look like a nut job didn't do it. Near the end of May and June, it started really getting hot up there so the ending was really, get the stuff in and running ASAP and fix it later.

It's surprising how little fan that 3 ton 16 SEER unit needs in low stage when it's 70F outside. Even high stage doesn't need much. I'm guessing when these units are engineered, they're using 95 degrees as the standard?