It could be that instead there's a busted discharge valve on the second cylinder. Either way the second piston doesn't seem to be providing any refrigeration effect.
Originally Posted by beshvac
If any of you pros don't have or have access to a psychrometric program or calculator, then you should think about locating one. It'll save a lot of head scratching. I have one posted in the educational forums, and there are several psychrometric apps available from itunes and the android market. You could also just use a wet bulb/enthalpy table and the total capacity formula
btuh total = 4.5 x cfm x ΔH
I don't see a airflow problem. Even if it was the condenser fan not going to high speed, you're still get a significant increase in capacity, but high head pressures and high amp draw.
IF inside airflow was a problem, you'd have low discharge air temps, not higher.
It seems clear to me that it's not generating capacity.
After all these service calls, if the intalling contractor hasn't figured out that the compressor is broken by now, Carrier should cut them off and not sell them anything more complicated than a single stage system until they get some remedial training for their technicians from an outside source...
Using the wet bulb temps & enthalpy chart I get 42,071.4-Btuh Low Stage &, 39,690-Btuh High Stage.
Originally Posted by rogressem
Hope I didn't make an error...it's easy to do...4.5* CFM * enthalpy change. The Low Stage should not be higher than the High stage; maybe I made a mistake somewhere?
If not; you got a real problem!
Last edited by udarrell; 07-07-2012 at 03:48 PM.
Reason: Low stage was a bit lower...
I think you got the enthalpy change to high.
Originally Posted by udarrell
With the conditions listed, the first stage enthalpy change is 6.7 btu/lb, and 2nd stage is 3.927 btu/lb.
Using that equation, 1st stage would be at 26,592 btu/hr, and 2nd stage would be at 24,740 btu/hr.
The psychrometrics app I use is corrected for my local conditions, but the variation from standard should only be slight.
The psychrometrics process calculator app I use, instead of that equation, gives slightly lower total capacity numbers, but they are within 1,500 btu/hr of the simplified equation.
I like using the process calculator because it breaks out sensible and latent capacity.
The way the system is operating now, it has higher total and latent capacity in 1st stage than in 2nd stage.
In 2nd stage the sensible capacity is slightly higher, but there is almost no latent cooling being done.
If there is a way to lock the system into only using 1st stage, I'd highly recommend doing so until the compressor is replaced.
I got similar numbers (about 26,000 btu/hr) for both. I'm using that Psychometrics app for iphone/android (maybe the same one your using), which also seems to match the regular enthalpy charts that I see. I'm pretty much at sea level (+14 feet I think)
I've been trying to figure out how to lock it in 1st stage until its fixed...not seeing a way to do that.
Originally Posted by mark beiser
Beginning to wonder that myself. I know this company has had some turnover lately, so I'm not sure how good their Carrier expertise is anymore (not a big company, so I know that must be a challenge).
I've already been looking at the other factory authorized Carrier dealers in my area, but I was hesitant with starting over with somebody new. I've also been giving them a break during this heat wave - at least I have some cooling!
Originally Posted by mark beiser
I agree, that locking it into 1st stage would be best. I'd also set airflow to maximum. This way you'll get the most capacity. On my newer controller,you can select low stage only form the advanced menus. I think it's in the system staging in under the lockout settings.
OK, here is the latest on this issue. Based on the info my local HVAC contractor passed to Carrier, Carrier concluded the TXV was bad. It was just in the 5 year parts warranty, so Carrier paid the cost of the TXV (I actually paid the difference and had the entire evaporator replaced with a newer aluminum Carrier N coil). No need going through all that and then have the evaporator leak in a year or so.
At any rate, made no difference at all, and I knew 10 minutes after they fired it back up. Same symptons:
1) Supply air temp goes up 5-10F from low to high stage
2) Delta T, measured at the evap is 10-14F in high stage, good 20 or so in low stage
3) Suction pressure always goes up about 10psig from low to high stage, head pressure essentially doesn't change. Local tech says Carrier told him this was OK, although the Carrier application and service guide for the 24ANA7 reads: "Suction pressure should be reduced by 5--10% when switching from low to high capacity. There should be a 10--20% increase in liquid pressure when switching from low to high capacity."
4) When I take careful and repeated wet bulb/dry bulb return/supply temps at the appropriate locations near the evaporator BTU calculations are essentially unchanged from low to high stage. (I've posted figures here before - no need to post them again - they didn't change)
Now, before Carrier agreed to replace the TXV, they did have the local tech come back out an check compressor amp draw (because he neglected to do that on the first visit). On a super hot day it was 6A low stage and just over 9A hi stage. Again, the Carrier service guide reads: "Compressor current should increase 100--250% when switching from low to high stage.", but this apparently didn't throw any red flags for the Carrier service rep, so they went with a TXV replacement
At this point, I'm waiting the local HVAC company to get a response from Carrier on the next step. I figure I probably have a good case. Carrier didn't agree to do an in-warranty TXV replacement if they didn't think something was wrong, and since the symptons have not changed, I wouldn't think that they could now say everything is OK. I still think its that Bristol TS compressor.
Here is my question: If I hit a dead end here, can I go directly to Carrier Mid Atlantic and start working this issue myself? Does Carrier have service reps that respond to things like this, rather than going through a local HVAC contractor?
No major complaints with the company I'm using - they are Carrier factory authorized, but I have the feeling they aren't the most experienced with these types of issues (they only have two techs). In most cases, I actually like dealing with a small company, but I think they may be in over their head on this one.
There is not one single thing about the readings you have passed on to us that would even hint that the problem was related to the TXV.
The compressor is clearly not functioning properly in 2nd stage.
It is ridiculous that this fiasco has continued this long.
The preemptive move to the all aluminum coil was a good call though, so there is that.
I wonder what part about a bad compressor there not understanding ,also i would refuse to pay for the coil replacement .
This is sad.
I just realized that you posted about the poor performance of this system just over 2 years ago, and it still isn't fixed...
For the record, I said the compressor wasn't working at full capacity in 2nd stage 2 years ago when you first posted about it.