Carrier Infinity 4 Ton - will I ever be happy

[hvacrmedic]

Yeah, I was thinking either a Bristol TS in 1st stage, or a 2 step scroll with a borked unloader.
I'm not a Carrier guy, so don't know by the model numbers what they came with.

The only 2 Infinity systems I've delt with were well after the customer gave up on the installing contractor. In both cases it was just minor stupid installation/setup details that were giving the system fits.

I'm a Carrier guy and I don't have them memorized either. There are too many to keep up with.

[tipsrfine]

I'm a Carrier guy and I don't have them memorized either. There are too many to keep up with.

So the sub-cooling is 15 no matter the conditions?

[tipsrfine]

Yea, thats what he told me, and I see it here (attached)

Here is a charging chart for your system. Check out Step 13, it shows the required subcooling does vary depending on conditioins.(I have no idea what that name plate means by 15 degrees subcooling). The charging chart shows subcooling can go from 8 to 18.
http://www.xpedio.carrier.com/idc/gr.../24ana-3si.pdf

[rogressem]

Original installer is coming out today since I agreed to a year on the maintenance contract. As part of today's maintenance he agreed to check all those temps that the other guy checked Thursday. I'll get his interpretation on that.

Here is a charging chart for your system. Check out Step 13, it shows the required subcooling does vary depending on conditioins.(I have no idea what that name plate means by 15 degrees subcooling). The charging chart shows subcooling can go from 8 to 18.
http://www.xpedio.carrier.com/idc/gr.../24ana-3si.pdf

[skippedover]

Here is a charging chart for your system. Check out Step 13, it shows the required subcooling does vary depending on conditioins.(I have no idea what that name plate means by 15 degrees subcooling). The charging chart shows subcooling can go from 8 to 18.
http://www.xpedio.carrier.com/idc/gr.../24ana-3si.pdf

That charging chart is on the unit but you have to pull the cover to see it. It's all right there for one who seeks the info. The User Interface can tell you only whether the outdoor unit has been commanded to run at first or second stage but not whether it's actually achieved that speed.

[hvacrmedic]

Here is a charging chart for your system. Check out Step 13, it shows the required subcooling does vary depending on conditioins.(I have no idea what that name plate means by 15 degrees subcooling). The charging chart shows subcooling can go from 8 to 18.
http://www.xpedio.carrier.com/idc/gr.../24ana-3si.pdf

It helps to know what you're looking at. The SC that you select at the top of the chart is the "required subcooling" and that would be what is listed on the nameplate, and that differs fom one model to another, and even from one size to another of the same model. The chart is for use across the entire product line, it's generic, thus the reason for the range from 8 to 18. In this case the required subcooling is 15°. You use the column below 15° and ignore the other columns. HTH. That chart is only for those who don't know how to subtract LLT from SCT. Ironically there is no 15° column, so you're expected to interpolate. I don't know how a tech who can't subtract is going to manage that, but there you go. That's how you use the chart.

There are also a range of favorable conditions under which that SC value is valid. Instructions are to weigh in the charge when conditions aren't favorable and come back later when they ARE favorable to trim the charge.

Oops, just relaized this is in the AOP forum. I hope this doesn't qualify as DIY info.

[tipsrfine]

It helps to know what you're looking at. The SC that you select at the top of the chart is the "required subcooling" and that would be what is listed on the nameplate, and that differs fom one model to another, and even from one size to another of the same model. The chart is for use across the entire product line, it's generic, thus the reason for the range from 8 to 18. In this case the required subcooling is 15°. You use the column below 15° and ignore the other columns. HTH. That chart is only for those who don't know how to subtract LLT from SCT. Ironically there is no 15° column, so you're expected to interpolate. I don't know how a tech who can't subtract is going to manage that, but there you go. That's how you use the chart.

There are also a range of favorable conditions under which that SC value is valid. Instructions are to weigh in the charge when conditions aren't favorable and come back later when they ARE favorable to trim the charge.

Thanks. Based on the chart, the subcooling seems correct, assuming the unit was in second stage when the pressure and temps were taken. I have no idea of what the pressure difference is between 1st & 2nd stage. I have no experience with 2 stage compressors.

[hvacrmedic]

Thanks. Based on the chart, the subcooling seems correct, assuming the unit was in second stage when the pressure and temps were taken. I have no idea of what the pressure difference is between 1st & 2nd stage. I have no experience with 2 stage compressors.

As a rule of thumb you can ballpark the expected SST in high speed by subtracting 35° from the indoor dry bulb temp. That also applies to single stage resi air conditioners. That would give us a SST of 44°. I use my own rule of thumb, indoor wet bulb minus 22°, which also gives us about 44° SST in this case. (Wet bulb is actually around 66°-67° at the stated RH of 53% and 79° dry bulb.)

[rogressem]

He completed the "tune-up", but wants to come back Monday to take some airflow readings. He said the compressor is shifting to 2nd stage, but the suction pressure is increasing when it goes from 1st to 2nd stage. He doesn't think there are ventilation leaks because the return grille and supply register temps have appropriate temperature differences from the air handler.

His numbers: (1st / 2nd stage)

Compressor amp draw: 5.5A / 11.2A
Liquid Line temp: 85F / 85F
Liquid Line press: 308 / 312
Suction Line temp: 64F / 68F
Suction Line press: 140 / 152

Suction Line Temp @ evap (only measured @ 2nd stage): 59-66
He said normal TXV fluctuation

Liquid Line Temp @ evap (only measured @ 2nd stage): 90

Return air temp (@ evap): 79F / 78F
Return air wet bulb: 65F
Supply air temp (@ evap): 54.8 / 62.3

Outdoor Ambient: 84F
Outdoor Humidity: 66%

[mark beiser]

I'm thinking the compressor has something wrong with it that is causing a lack of capacity in 2nd stage.

The suction pressure should have gone down, and the liquid line pressure up by more than 4 psig, when it changed to 2nd stage.
There should also not have been a drastic rise in the supply air temperature in 2nd stage.

[comfortdoc]

How long was he there and did he do any other work as part of the tune-up?

[rogressem]

Probably 2 hours. Did the other usual things, cleaned the condenser coil (was already clean), the cursory spraying of cleaner on the upper surface of the evap coil, looked at the bottom side as best he could (it was clean), checked amp draw on blower motor, condenser fan and compressor, condensate line cleanout, read the trouble codes off the controller (saw a 71 and 72, thermal cutout low stage and hi stage - from last summer, but he said that was a known issue with the original board at the condenser).

I think the is the first time they've actually done comparisons from 1st to 2nd stage.

How long was he there and did he do any other work as part of the tune-up?

[rogressem]

The latest on this. My local HVAC company has conferred with Carrier, and they believe the TXV is bad. Carrier had them come back out and double check the amp draw on the compressor, since these Bristol TS compressors have had issues. Low stage: 5.6A, Hi Stage 9.2, so the thought is the compressor is ok.

They will replace the TXV in a couple of weeks, (waiting for the part).

I can't reason in my head how they get good subcooling and superheat values at hi stage, and the TXV not be working. I would have bet money that it was the compressor (suction pressure goes up low to hi stage). Carrier is replacing the TXV at their cost - so I can't argue with that. I'm just happy that they finally acknowledge something isn't right.

Will post an update after it is replaced.