What is the deltaT test for a PTAC AC?

Question

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

Answer 1

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.