Lennox 3ton Rooftop question.

[budman21901]

Lennox RTU
M#LCH036H4EN Y
S#5611H05061

Copland Scroll 2 Stage
M#ZPS30k4E-TF5-130
S#11AG38D4N
410A

Unit is new and was just set a few months ago. Checked Prodigy control and find 2 Low pressure switch faults, and the third had locked it out. Reset system, and checked operation. System runs perfectly in 1st stage cooling. Pressures are great, Comp, fan and blower amps all within range and at proper speed. Everything is running according to design.

2nd Stage Cooling kicks in. Blower and fan ramp up, amp draws are still doing great, and Suction just drops off the radar. Discharge Pressure remains constant and acts normal. Suction drops to 70psi.

This is a single circuit system. Every component is used in 1st stage as 2nd stage. Only component that changes is the compressor. I am thinking the bypass ports are not closing and the compressor remains at 67% capacity. With the increased blower speed suction is falling off. I have never seen this before, so any input you guys have is appreciated.

OAT 78'
SAT 66
RAT 78'

1st stage
Pressures 125-325
Comp 4.7A
Fan .9A
Blower .76A
Superheat 18'
Subcooling 12'

2nd Stage
Pressures 70-325
Comp 6.42A
Fan 1.1A
Blower 1.8
Superheat 54'
Subcooling 13'

One thing i did not do was remove charge, and recharge to factory specs. I recommended that we rule that out before we condemn anything. I see no signs of oil anywhere, and I checked pressures according to unit chart and everything is up too par. I truly don't believe this is a charge issue.

http://www.youtube.com/watch?v=uPhthHuZsQk

[timebuilder]

Are you sure this is a digital scroll?

I haven't seen these yet in the small RTUs.

[budman21901]

Are you sure this is a digital scroll?

I haven't seen these yet in the small RTUs.

Not a digital. Its the new Ultratech series. I provided a link at the bottom of the first post of how it works.


http://www.emersonclimate.com/en-US/...ng_system.aspx

https://www.google.com/url?q=http://...7TKUYGm6YQBNvA

[timebuilder]

Well, it's a good thing it's locking out with superheat that high.

With the variable speed compressor, are they using an EEV?

[AiResearch]

Your compressor current is increasing on high capacity, so it would seem the load / unload function is working.

This is an ECM direct drive blower motor?

Have you verified all of the correct settings in the Prodigy controller?

The temp conditions posted look pretty mild..

Your suction pressure drops off and the SH goes way up on high stage..

It appears the valve is not feeding enough refrigerant for full capacity.

Maybe pop a new power element on there and see what happens.

Or a small shot of refrigerant?

[AiResearch]

The Copeland ultratech is just a solenoid activated load / unload scroll that provides a thirty something percent capacity drop.

That unit should have a non-adjustable Sporlan with a removable power element.

[timebuilder]

The Copeland ultratech is just a solenoid activated load / unload scroll that provides a thirty something percent capacity drop.

That unit should have a non-adjustable Sporlan with a removable power element.

That's what I thought, too, but the info links he posted says "variable speed," not a "scroll lifter" like the digital scroll. Of course, the link info may not apply to that unit...

[limmy09]

whats the duct work look like

[AiResearch]

That's what I thought, too, but the info links he posted says "variable speed," not a "scroll lifter" like the digital scroll. Of course, the link info may not apply to that unit...

Think that may actually be a typo on the Emerson sight. That picture looks like the regular old 2 stage solenoid load unload compressor and so does the circuit board. Those have been out for years.

The new variable speed compressor and controller look a bit different from what I have seen and read, although I have yet to get my hands on one.

And its certainly not the digital "lifter" scroll which is constant speed with multiple capacity steps.

Maybe someone on here can clear up the latest Copeland scroll technology.

Have seen the two stage and digital scroll in small rtu especially in OA units, Aaon for example.

[budman21901]

whats the duct work look like

Very simple. Drops straight into a room, and return pulls from the room. No duct issues at all.

No EEV, but just a normal TXV which i have diagnosed as operating properly. Again, this is a single circuit with the new ultratech Technology. First i have ever seen, but all i can come up with as a possible cause. I have checked this thing inside and out! Including all sensors on prodigy controller. SAT sensor seems to be a little out of wack to my readings, but that is the least of my problems at the moment. I have not totally ruled out a charge issue yet. I didn't have the equipment on site to remove charge, and recharge to factory specs. I did put unit into high mode, and check subcooling, and chart for units discharge pressure and all corresponded to what i was seeing. Guys this one is just off the wall for me. I won't sleep till i get to go back and figure this one out! LOL

[AiResearch]

Very simple. Drops straight into a room, and return pulls from the room. No duct issues at all.

No EEV, but just a normal TXV which i have diagnosed as operating properly. Again, this is a single circuit with the new ultratech Technology. First i have ever seen, but all i can come up with as a possible cause. I have checked this thing inside and out! Including all sensors on prodigy controller. SAT sensor seems to be a little out of wack to my readings, but that is the least of my problems at the moment. I have not totally ruled out a charge issue yet. I didn't have the equipment on site to remove charge, and recharge to factory specs. I did put unit into high mode, and check subcooling, and chart for units discharge pressure and all corresponded to what i was seeing. Guys this one is just off the wall for me. I won't sleep till i get to go back and figure this one out! LOL

Just wondering, are you sure the expansion valve is okay?

A new power element sometimes works wonders.

Perhaps the sensing bulb was overheated, or maybe lost a portion of its charge.

[budman21901]

Your compressor current is increasing on high capacity, so it would seem the load / unload function is working.

This is an ECM direct drive blower motor?

Have you verified all of the correct settings in the Prodigy controller?

The temp conditions posted look pretty mild..

Your suction pressure drops off and the SH goes way up on high stage..

It appears the valve is not feeding enough refrigerant for full capacity.

Maybe pop a new power element on there and see what happens.

Or a small shot of refrigerant?

Yes direct drive.
Yes, all setting verified in controller.
Yes, SH/SC normal on first stage. SH high, and SC normal on 2nd stage.
Whats this power element you speak of? Please explain?
Yes, I am going to weigh in a charge next time i am there. I would love if that worked, but just don't think that is it.

[budman21901]

Just wondering, are you sure the expansion valve is okay?

A new power element sometimes works wonders.

Perhaps the sensing bulb was overheated, or maybe lost a portion of its charge.

Its a TXV with a sensing bulb. Please help me understand this if it applies Its not a EEV if that is what you mean.

[budman21901]

I am attaching a PDF of the actual unit specifications. Thanks everyone for the replies.

http://home.comcast.net/~budman21901/lennox.pdf

[AiResearch]

budman if you get some time, do some reading on thermal expansion valves and how they work

you will then see how, if a power element and sensing bulb were to loose some or all of its charge, or experience some other type of problem, it will fail to open the valve enough, or at all, resulting in low evaporator pressure and high superheat

the power element / sensing bulb can be replaced without removing the valve itself on that Sporlan that is in the unit you are working on

there is a fair chance that is your problem IMO based on the info you have given and experience with that equipment

good luck

if this unit has the humidity control option with reheat coil, there could be other issues

[budman21901]

budman if you get some time, do some reading on thermal expansion valves and how they work

you will then see how, if a power element and sensing bulb were to loose some or all of its charge, or experience some other type of problem, it will fail to open the valve enough, or at all, resulting in low evaporator pressure and high superheat

the power element / sensing bulb can be replaced without removing the valve itself on that Sporlan that is in the unit you are working on

there is a fair chance that is your problem IMO based on the info you have given and experience with that equipment

good luck

if this unit has the humidity control option with reheat coil, there could be other issues

Thanks for the info. No there is no humidity option. I know exactly how a TXV works. They are just not called power heads here, or i have never heard them called that. Diagnosed them many times, I see your point though. It very well could be a TXV issue. When the extra refrigerant is introduced into the system it stays stuck dropping suction pressure, and causing the restriction. In low stage blower is on low, and Condenser fan is on low, and comp running at 67% Problem is unnoticeable. I checked that TXV, but is it opening enough?? I like that diagnosis much better then mine and i will triple check that TXV next time i am there.

I think new technology causes us to over think things, and not go back to the basics of refrigeration. Now i need to check that TXV more thoroughly because i can see exactly how that could be the issue! Thanks, and i will let you know..

[limmy09]

whats the time between stages, does it shut down or just kick in to high gear. what if the txv is not acting fast enough. are you putting in to second stage or is the tstat

[budman21901]

Sorry for not getting back to this earlier. I moved so i have been busy and just got internet hooked up at my new house. Anyways, i replaced the TXV and it solved all the problems. The TXV must have been stuck just enough to allow movement in first stage, but when second stage kicked in and introduced refrigerant capacity the TXV just didn't open and suction would drop off. TXV was the issue, and thank you for all your help..