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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8769
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I am an HVAC contractor in Southern DE. I have a performance

Customer Question

I am an HVAC contractor in Southern DE. I have a performance issue with a York system that another contractor installed and after going through a few things I believe they mismatched the outside and inside units. I have model and serial numbers. Can you help with that?
JA: Are you an HVAC professional?
Customer: Yes
JA: Do you plan on doing the work yourself?
Customer: I am not sure, that will be up to the homeowner to decide if they want me/ my company to fix or if they will contact the installing company.
JA: Anything else we should know to help you best?
Customer: Well I have what I believe to be a 4 ton outside unit with a 5 ton inside unit. ECM motor set to medium high speed as per installation manual. 80 degree ambient temperature 61degree indoor wet bulb temperature, 7 degrees super heat and 3.2 degrees subcooling. 280PSI liquid line preassure and 127-134 PSI suction line pressure.
Submitted: 2 months ago.
Category: HVAC
Customer: replied 2 months ago.
This is a York System, Inside air handler is Mod.AHE60D3XH21B Outside unit is Mod. YHJF48S41S5A. TXV system No super heat adjustment on TXV. R410 of course. Factory subcooling should be 8 degrees with current conditions,its not even close.
Customer: replied 2 months ago.
Double checked TXV bulb, it is secure and insulated, condenser coil clean and with those pressures I am pretty sure the charge is really close!
Expert:  Phil replied 2 months ago.

Hello, I just need the model numbers of the coils and condensing units, not the serial numbers

Regarding super heat, only number that really counts is when the system is down to operating temperatures ...not when the building is still hot.

I need to know the supply and return air temperatures, the indoor air temperature and the outdoor temperature then the head and suction pressures at the *exact same time

We can go from there

I am a retired mechanical engineer and HVAC/ electrical/ refrigeration and boiler contractor ... with 56 years in this business. The last 20 of those years consulting for major firms nationally...All I ask is please select the ***RATING LINK***at the top of your page, that is the only way I am credited through the site. Rating does not affect your charges nor ability to refund if not satisfied.

Customer: replied 2 months ago.
I sent all that information! indoor wet bulb and outdoor dry bulb. I also sent suction and liquid pressures, as well as inside unit numbers and outside unit numbers, did you not get them?
Expert:  Phil replied 2 months ago.


Expert:  Phil replied 2 months ago.

I need the indoor dry bulb temperature

at 72F indoor dry bulb the suction pressure should be 101 psig on R 410A

Customer: replied 2 months ago.
Okay, here it is! outdoor dry bulb temp,80 degrees, indoor wet bulb 60-61degrees. Liquid pressure 278-290 psi, suction pressure 127-134 psi super heat between 7 and 10 degrees (total) subcooling 3.2-5.5 degrees. TXV system York outside unit Model YHJF4841S5A inside unit number AHE60D3XH21B ECM blower mtr set to medium high speed return air temp. 72-73 degrees supply air temp between 59.9-62.3 dgrees. According to factory plate I should have 8 degrees of subcooling for current conditions not even close. charge is good. TXV bulb is tight and insulated.
Customer: replied 2 months ago.
Hey Phil you still with me or did you go to sleep?
Expert:  Phil replied 2 months ago.

Thanks, at 80F outside air the unit should be condensing at 341 psig, 25F hotter than outside air on a SEER14 system (click here please)

At 270 psig head pressure is not taken accurately, OR the system was vapor charged with R410a not liquid charged, Or the compressor discharge check valve (scroll compressor) is going bad.

its a bit of a mess.

However with a suction pressure of 130 psig~ and the room at 72F the suction pressure is way high (29 psig high), all that pointing to your suspicion that the evaporator coil is over sized, you could compensate for that by reducing the air flow by 15 to 20% no need to replace the coil at this point. I will look up the model numbers next

Factory charging information is useless if the equipment is mismatched... also useless if the air flow is not measured. However we can get around most of that.

Customer: replied 2 months ago.
I completely agree concerning the factory charge information. I have looked up the system on Yorks site and they confirm that the inside coil and TXV are 5 ton units and the outside unit is a 4 ton unit. I do not think this was vapor charged. I believe they opened the service valves and walked away from it, unless York did it. The unit is only 3 years old. I question why you think the suction pressure is way too high? thats 42-44 degrees of evaporating temperature, pretty normal really. Liquid pressure is completely accurate, I can assure you of that!
Expert:  Phil replied 2 months ago.

See the R410a pressure temperature chart I attached earlier, at 80F outside and assuming a SEER 14 unit, it would be condensing at 25F hotter than the outside air (105F condensing is 340 psig head pressure)

271 psig head condensing would be 89F condensing temperature that would happen on when it was 67F outside... 271 psig is way low. something is wrong there, The york model number YHJF4841S5A did not come up for me, if this was a two speed system, the low head pressure would make sense.

If the contractor mis matched the coil and condensing unit there is a good chance that he vapor charged with R410a not liquid charged, that will throw all the numbers off. We can keep that in the back of our head for now.

The suction line with the room at 72F DB, should be sweating all the way back to the condensing unit, but NOT onto the compressor itself, that is a more reliable guide than super heat measurement when the system is running at temperature for best dehumidification, (the factory numbers are for highest efficiency so they can advertise it but not best dehumidification and most especially with the indoor coil 20% over sized.

Tell me the brand and model number of the TXV please...

We can go from there

We will have to work with this for a while

Expert:  Phil replied 2 months ago.

I will be out for an hour, slow the air flow down 20% lets see if we can get the suction pressure to 101 psig with the room at 72F dry bulb and 15F delta T across the coil.

We can sort out this head pressure anomally as we go along.

Customer: replied 2 months ago.
I did check the condensing delta and it is only 13 degrees, TXV is a Sporlan I believe, SI-ITVM4J1 with a ZGA bulb charge. I did have suction line sweating back to the outside unit, I did not check to see if it was all the way to the compressor but I suspect it was pretty close. I have left the home and I am back at the shop so I can't reduce the air flow. I also have to be careful to not do anything that may give the installing contractor any reason to NOT honor the system warranty. I was merely asked to check the system and report on my findings. I am not sure slowing the airflow is the answer to a mismatched system long term. This is a fairly large house with the inside unit located in an attic above the second floor. I do believe that there is already a reduction in air flow due to the fact that there is one 16X25 filter in a return grill. Way too small for 1750 CFM or close to that. I appreciate your help, my recommendation to the home owners will be to contact the installing contractor to have him match both units and add additional returns
Expert:  Phil replied 2 months ago.

That recommendation you want to give is safe enough for you and should work for the system, if you were going to tweek it though, you can generally get to the internal expansion valve adjustment through the flare nut on the outlet end, turn it in 1 full turn, that will starve the coil so that it will work better with a 4 ton condensing unit.

There will be no liability in that mechanically, same with slowing the air down 20%,

If that 270 psig head pressure is accurate, either its a two stage compressor operating on low stage, OR something else is incorrect, Head pressure at 80F outside requires a *coil temperature 25F hotter so thats 105F and 341 psig head, (the air off the coil however will only be 15F hotter)

Someone may have put some R22 into that system... watch out.

please select the 'finish and ratey our expert' link near the top of your page to close the question, I will appreciate it.

Your positive rating is the only way the company pays me for my work, lacking that I work at a loss. Thanks!