New Condenser, Old Evaporator, functioning data

[blank_disk]

I finally had a tech adjust the freon charge in my Frankenstein 5 Ton 13 SEER New Nordyne condenser with 5 ton 31 year old evaporator using TXV.

There was a LOT of debate on this site about the merits, and efficiency/inefficiency of such a system.

I had the charge adjusted, and got the tech to write down all the numbers.

Here's what he got:

High Side, 223psi, (108 *F), measured temperature 99.5 *F
SC= 8.5 *F

Low Side 70-72 psi (38- 39 *F) cycles every 30-60 seconds, measured temp 63.7 *F
SH = 24.7 to 25.7.

Because of the TXV he charged to the chart provided by Nordyne for TXV. It calls for a about 9 *F SC at 225 Liquid Pressure.

The outdoor temp was 90*F.

Static pressure air handler, 0.65 inch.
(Manual says 0.50 inch MAX.)
Chart suggests at 0.65 inch water, about 1855 CFM.
Indoor Return 76 *F DB, 66 *F WB
Vent 57.5*F DB, 55.2*F WB.

Delta DB = 18.5 *F

The superheat seems high. I asked him if he could adjust the TXV. He said because of the way the evaporator was installed in the attic, it will be difficult to access the valve. (Plus not sure about the wisdom of adjusting a 31 year old part!)

Would you recommend adjusting the TXV to get superheat lower?

I have budgeted to replace the indoor coil and air handler before next summer's cooling season. Do you think I will be OK with the above operating conditions for the rest of the summer in Dallas Texas?

[beenthere]

Since the TXV isn't maintaining a steady vapor pressure.

No way to tell from here.

[blank_disk]

Since the TXV isn't maintaining a steady vapor pressure.

No way to tell from here.

You feel that a 2 PSI variation is significant?

[Shophound]

I can't see how Nordyne's chart can apply to mismatched equipment. How can they know how a brand new condenser of their making will perform with a 31 year old evaporator? Answer: not only can they not, it's not on their radar.

Going strictly by your numbers given it would indicate an evaporator running starved, which accounts for both the high superheat and the hunting TXV.

Before your tech adjusted the charge, did he record or comment what the superheat was running at prior to any changes?

Will your system make it the rest of this summer? All I can say is that if the way your system is performing right now, with high superheat, you're not doing the compressor any favor. The 31 year old evaporator isn't the most kind thing it can be hooked to, either.

[amd]

Based on what you've posted, duct improvements might be required to move 2000 CFM.

Variable speed blowers can compensate for undersized ductwork to an extent, at the expense of efficiency and motor lifespan.

[beenthere]

You feel that a 2 PSI variation is significant?

If the system was operating correctly. It wouldn't have that 2PSIG hunt.

[Airmechanical]

SH = 24.7 to 25.7---The superheat seems high.

ya think?



.

[rayr]

But the big question is, where were the SH measurements taken?????