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I have a PTAC AC that blows cold air, but barely cools the room. The landlord is claiming its because the room is the livingroom and its an open to the kitchen and hallway.

I know that the rule of thumb for a functional central AC is a 20 degree F delta between the intake and outtake of the AC unit itself. But the PTAC itself has the intake on the bottom and the outtake in the top of the unit.

Question is, what is the HVAC standard for measuring the deltaT? How far should it be taken from the outtake? Or should it be done right at the intake below the unit?

This is an old unit that had the compressor replaced about a year or two ago. I have noticed that the outtake of air is not uniform, and there are significant gaps with weak air coming out.

AC's outtake is about 26" long and 6" wide. The first 2" to 4" from the left dont output much air, the 6" to 8" after it does, then another weak air outflow for another 7"-9", then again, about 6" (or so) of good air flow out, then the last 2" to 4" dont output much. What could be the issue with that?

  • Refrigerant (R22 oz): 28.2
  • Voltage: 230
  • Cont Mtr AMPS: 0.79
  • Cooling BTU/hr: 16,900
  • Total cooling Amps: 7.30
  • Total Cooling Watts: 1,743
  • Compressor LRA: 38.00
  • Compressor FLA: 6.20
  • Evap. Motor Amps: 0.29
  • Heating BTU/hr: 0
  • Heating Amps: 0.00
  • Heater Mtr Amps: 0.29

Test pressure

  • High side: 300 psi
  • Low side: 150 psi

Max fuse size: 20 Amp time delay on HACR type circuit breaker

  • If you can get the make and model number, someone could probably do an internet search and come up with the specs for you. – FreeMan Jul 28 at 23:16
  • @FreeMan i couldn't find a spec. Thats not something that is readily available – KingsInnerSoul Jul 28 at 23:17
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    At 16900 btu I would expect your unit to cool both rooms, possibly not with the oven on but cool yes, time to look at cleaning and possibly straightening fins that are bent, bulb position for txv would be my first checks if the temps at the suction and discharge of the compressor look good. – Ed Beal Jul 28 at 23:46
  • Ed, when an HVAC technician came by few weeks ago they used a brush to remove any accumulation of dust in the fins, as well they blew compressed air in the intake and outtake. The fins at the intake look straight for about 90 to 95% of the total area. What is the bulb? – KingsInnerSoul Jul 28 at 23:56
  • If it has a txv or thermal expansion valve this controls the flow of refrigerant when the evaporator gets cold the valve closes, there is a small tube going to a “bulb” of metal the bulb is a chamber as the temp drops or raises that chamber opens or closes the txv (not all systems have these) some use capillary tubes or orifices to control the flow of your system use a txv there will be a thin tube going to a bulb usually these are positioned very close to the evaporator a few times I have seen them in contact and that reduced the cooling, some even have a plastic sleeve to prevent contact. – Ed Beal Jul 29 at 13:35
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10k btu should cool a fairly large room but 2 rooms maybe not, I found that the problem with these units is the filters get plugged up and removed then the coils get plugged up with dust and they don’t work as well.

A 20 degree delta +-2 is a good rule of thumb for a clean unit and if your unit has a txv or thermal expansion valve sometimes a slight adjustment will allow for a larger delta. It could have gotten bumped when it was serviced or cleaned by others the bulb in solid contact turns off the flow of refrigerant two far away two much flow the coil will ice up (this happens when really dirty also).

Can you shine a flashlight behind the coils and see the light if you open the filter housing? Or looking through if no light passes it could use a cleaning.

A can of aerosol coil cleaner is less than 10$ at most big box stores a can may be enough for your unit. (The can may show a window ac that’s ok your unit is really a very high end window unit put in the wall) .

Don’t be tempted to use vinegar acids etch the fins and eat the galvanized coating then they start rust. I think foaming cleaners are the best they push the dirt and dust out. If there is or was a smoker in the house get 2 cans smokers really plug the evaporator coils but they clean up really well.

Since the unit was recently serviced I would expect it to be in good shape but a clean unit will cool much better than a dirty unit. As we hit temp extremes the delta may drop a bit but should be 20 for most systems and can be much higher but this brings other issues like freezing up excessive condensation on the discharge side.

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  • I have updated the post with more details – KingsInnerSoul Jul 28 at 23:38
  • Ed, the AC's outtake is about 26" long and 6" wide. The first 4" from the left dont output much air, the 6" to 8" after it does, then another weak air outflow for another 7"-9", then again, about 6" of good air flow out, then the last 2" to 4" dont output much. What could be the issue with that? – KingsInnerSoul Jul 28 at 23:51
  • The areas of low output may be due to dirty coils it can also be caused from icing. ice blocking the air flow Can reduce the delta T also. Last it could be the design but normally they use a squirrel cage blower or 2 so the flow is uniform but split in the case of 2. – Ed Beal Jul 29 at 13:47

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