My temperature difference between my supplies and returns is only around 5 degrees F. I opened up my air handler to see if the evaporator coil was dirty, and it was clean -- but running the outside unit (condensor) without running the air handler, I expected the evaporator coils to get very cold - to ice up, right? Well they got cold, but nowhere close to icing, and I suspect that's the reason my delta-T is only around 5F.

So this is after I just had the refrigerant completely recharged -- what could be any other issues as to why the coil isn't ice cold?

Edit: I've cleaned the condensor fins already. The whole system is around 20 years old (I know, it's ancient)

Edit: I had the HVAC guy come and check. I'm at 25 psi on the lines, so yeah I have a leak. Not sure why he didn't see the leak before. Waste of money though.

  • Generally the target temperature of the coils is a few degrees above freezing, to prevent ice buildup. Even if the coils were colder than freezing, it would require enough humidity in the air to condense and freeze. In a dry climate you may not see that. You said you cleaned the coils, did you also replace the air filter?
    – mfarver
    Commented Jun 15, 2020 at 1:30
  • I should've stated I live in Florida, so definitely enough humidity - around 70-80% most days. I've put new air filters in it. The way I checked the temperature of the coils is by placing my hand on them - basically I shorted the thermostat's red and yellow wires to turn on the condensor without turning on the blower. I then held my hand on the evaporator coils for around 2 minutes, and I noticed them getting cold but not super cold
    – Tyler M
    Commented Jun 15, 2020 at 2:27

1 Answer 1


You never want the coils in the evaporator to ice up. Ice can damage the coils and reduces the airflow. More often I find dirty coils outside many times filled with dust so they are not cooling the refrigerant. A 5 degree delta sounds small but is meaningless without the air temp , with a system this old an 80 deg outside temp you should be closer to 15-20 degree drop. My guess would be that you are low on Refrigerant so the system doesn’t have the volume of high pressure liquid to be released and create the cold you are used to. You probably have R22 and it is Running ~100$/ lb , I have heard higher in some areas but it can still be purchased a 5 ton system may take ~ 8-10 lbs to bring back to full cooling, and they will probably try and talk you into updating to a new refrigerant basically a new system.

  • Thanks Ed. Return temp is about 90F and supply temp is around 85F while running. Temp on the evaporator fins, best guess, is around 60F. This is after I'd tried cleaning the condensor (outside) coils. We just had 10lb refrigerant put in about a week ago, and didn't run it until yesterday when so we noticed the small delta -- hopefully there's not a leak. Having HVAC guy come back out today to check the pressure make sure it's not leaked.
    – Tyler M
    Commented Jun 15, 2020 at 14:09
  • That would be a huge leak to loose that much in a week. The only positive thing is it should be easy to find the leak
    – Ed Beal
    Commented Jun 15, 2020 at 18:20
  • HVAC guy checked, i'm at 25 psi, so yeah it's a pretty big leak. I don't know how but he didn't find it last week when he filled to 300psi with nitrogen. He said he didn't 'hear' anything leaking -- i guess that's good enough? Not sure why the guy didn't use any UV dye to check, but I"m basically in the same boat I was in a week ago - No refrigerant, no idea where the leak is at, I'm just less $500
    – Tyler M
    Commented Jun 15, 2020 at 18:58
  • Wow , I don’t usually use dye once it gets on your gear ,,, if he both pressurized the system and then pulled a vacuum that should have been obvious on the gauges, if your system is r22 and he put in 10 lbs he was not intentionally ripping you off I just find it hard to believe a leak that large would not be seen with a pressure or a vacuum leak check. You might ask him to try a dye from what you have said it sounds like he did try and may try again, I know I would not want that for a reference (I believe most do try to do a good job).
    – Ed Beal
    Commented Jun 15, 2020 at 19:25
  • I checked over his shoulders, and the gauges did hold steady after 20min at 300psi nitrogen. Maybe I should give the guy more credit - I do believe he did try to find a leak. I was just upset that today after coming back he didn't attempt to look for the leak now that there's obviously a leak.
    – Tyler M
    Commented Jun 15, 2020 at 19:30

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