Strange manifold pressures ?

[deadeye52]

Hi: I replace a leaking evap. coil in hud house miller heater. Got a "A" coil almost exact dimensions, except its a 3 ton in place of 2.5 ton evap., fit like a glove. Installed new 2.5 ton 410-A condenser. installation paper said. r22= .73 piston, 410-a = .67 piston.
So I went with smaller piston. A little longer line set also. After running 15 minutes had 250/155 at manifold gauges. Only 4 degrees of super heat. 85 degrees outside dry bulb. only 5 degree's diff. off top of condenser fan. Was thinking of changing to smaller piston. any thoughts, thanks.

[mgibbs]

What are the temps inside. Return air db, wb and supply

[deadeye52]

The homeowners were leaving on a trip as I finished. indoor dry blub was about 83 degrees, 64 degrees coming from floor registers.

[KevinAdv]

does not sound bad but maybe try to go back and check under normal conditions

[deadeye52]

Yeh: I'm going back Monday. It will still be around 80 degrees outside. Hope the homeowner doesnt says its cool, but never shuts off. If that's the case , I guess my next move would be to put a smaller piston in evap.

[gravity]

You need to get return wb and charge by target sh. You either overcharged it. Or its your typical hud house low airflow issue.

Sent from my SM-N900V using Tapatalk

[JKerch]

Personally, I would have installed a txv on a mismatched unit just to let it take the work out of guessing.

[Todd Whaley]

Seeing mismatched units a lot with the wrong fan speed.

[r-290]

need
Indoor Wet Bulb
condenser dry bulb
vapor pressure
vapor lime temp.

if you have a smart ph, down load check and charge

[beenthere]

The chart you looked at was from the evap coil, and not the condenser. That chart was for a 3 ton system, not a 2.5 ton. So you have a 3 ton piston in it, but only a 2.5 ton condenser.

Look at condenser to see if it list a piston size, or only TXVs. Take a 59, 63 and 65 piston with you and see which works better if the condenser does list a size.

[hvacrmedic]

Hi: I replace a leaking evap. coil in hud house miller heater. Got a "A" coil almost exact dimensions, except its a 3 ton in place of 2.5 ton evap., fit like a glove. Installed new 2.5 ton 410-A condenser. installation paper said. r22= .73 piston, 410-a = .67 piston.
So I went with smaller piston. A little longer line set also. After running 15 minutes had 250/155 at manifold gauges. Only 4 degrees of super heat. 85 degrees outside dry bulb. only 5 degree's diff. off top of condenser fan. Was thinking of changing to smaller piston. any thoughts, thanks.

If you don't know how to charge a piston metered system, then a different piston won't help. Google "How to charge a piston metered system".

https://www.google.com/#q=How+to+cha...em&safe=active

[deadeye52]

The space may be to too limited for a trx valve. The system is not over charge, with no frigerant add and long line set. The condenser came with two pistons ( .60 & .61) , they are too small to fit in evaporator receiver. I did buy a .61 from supplier Saturday that will fit. With some of your suggestion, I think I will pull back charge, swap piston. Maybe reuse dryer, then a good evac. Hopefully pressures will look better and super heat will also.

[beenthere]

Ah, so you used the 3 ton piston that came with the evap coil. That will over feed the evap when using a 2.5 ton condenser.

[EMETH]

The space may be to too limited for a trx valve. The system is not over charge, with no frigerant add and long line set. The condenser came with two pistons ( .60 & .61) , they are too small to fit in evaporator receiver. I did buy a .61 from supplier Saturday that will fit. With some of your suggestion, I think I will pull back charge, swap piston. Maybe reuse dryer, then a good evac. Hopefully pressures will look better and super heat will also.

Because of THIS, we spec all new construction by contractors have TXV external of AHU:

[r-290]

Because of THIS, we spec all new construction by contractors have TXV external of AHU:

FWIW the only part you would see is the bulb.

All the carrier/bryant and trane/AS txv's are factory installed and are inside the cabinet.
maybe spec some equipment with them installed at the factory?

Here you have somebody that was not willing to make a run to the parts house to get the proper part, a teflon ring to make a good seal. They decided to "fix it". Well you can see the results.

[Linktorn]

The chart you looked at was from the evap coil, and not the condenser. That chart was for a 3 ton system, not a 2.5 ton. So you have a 3 ton piston in it, but only a 2.5 ton condenser.

Look at condenser to see if it list a piston size, or only TXVs. Take a 59, 63 and 65 piston with you and see which works better if the condenser does list a size.

X2 my chart says 59 for 410a 2.5 ton

[deadeye52]

Put the smaller piston in and it ran like a champ, thanks for all the help.