I have a re-occurring issue with my central air. I have changed filters, cleaned all three intake vents and even had a serviceman out on three different occasions (two separate companies). My problem is low air pressure out of the cooling vents, and the outside line freezes up within one to two hours. The temperature in the house is anywhere from 80 °F to 85 °F, even though the (digital programmable type) thermostat is set to anywhere from 77 °F to 79 °F. After a couple of hours there is no change in temperature, less air pressure and a frozen line. All three serviceman say the Freon levels are good and air pressure is good, yet my home doesn't cool down.

This is becoming a costly issue with no coolness in sight. What's your suggestion?

Note: I have two adults, five kids and three dogs, and have never had this problem in any homes before.

  • 1
    Sounds like you may have a blockage inside the ducts somewhere. Do you have any dampers on your ducts? It would appear as a small lever on the side of the duct work.
    – BMitch
    Commented May 22, 2013 at 22:32

3 Answers 3


List of possible causes and fixes:

  • Insufficient airflow.

    You have identified this issue but not the cause.
    1) Take all air filters out of the system. Give the system 30-40 minutes and see if this fixes the issue.
    2) Ensure all vents are fully open.
    3) Verify and/or adjust the cooling blower's air speed. WARNING: Turn the power off to the HVAC before doing that. The only way to verify or adjust the speed is to get the manual and find the table that lists the dip switch settings. Somewhere on the circuit board under the cover of your air handler there will be a tiny block of dip switches that control various things like the blower's speed for cooling and heating. A lot of shady service men will set this too low and continue to charge you for service calls. Then there is the group that doesn't even know it exists. ugh.. If you do change it set it to the middle-high setting. Usually there is low, medium-low, medium-high, and high.

  • Leaking freon.

    You might have a tiny pin hole in the copper some where. Your service guys indicated this was ok. If you trust them then this is not the issue.

  • Copper tube is not covered with insulation.

    Go to the box store now and get some black "pipe insulation" where the copper tubes are located and then cut it to cover the tube. This is a four minute job and will at least prevent the tube from freezing; which can damage your system by the way.

  • You condenser coils are ineffective because they are full of debris like grass and dirt.

    The condenser is the big unit outside and if its clogged with dirt it will not allow the freon to release its captured heat from your house. You can fix this yourself by either spraying the coils with a water hose or by renting a pressure washer that allows you to add soap to the water slowly. This happened to me last year because of grass clippings and dirt build-up and this can happen to anyone regardless of the age of the HVAC system.
    1) Make sure you spray from the inside out. You must take the cover that holds the fan off and the shroud/cage off too. Why? Because if you spray from the outside towards the inside your just pushing the debris further into the coils possible lodging it in there forever.
    2) If you go for the pressure washer DO NOT get too close with the nozzle. If you put too much pressure on the coils they will fold and you'll ruin your unit. Pressure washers come with various sized nozzles and you should use the biggest nozzle first and if it isn't working then move your way down to the next smallest nozzle. Bigger nozzle = less force. Either way you need to get some soap mixing with the water at a good pressure in order to clean the coils. Its best if you take the shroud off so you can get to every square inch of the coils.

  • Your compressor or fan is not turning on.

    1) Check the wires that run to your unit. A lot of times there is no cable management for these wires and they are just dangling in the elements as they run from your house's foundation to the unit. They can easily be cut by a weed-wacker. Re-connect/solder if this is the case. Make sure you use some heat shrink tubing to protect the connection from the elements.
    2) Your relay switch is broken. Lots of times small critters crawl into the relay and get electrocuted when the relay kicks in causing a small explosion that's powerful enough to crack and melt the plastic relay and the metalic parts just enough that it stops functioning. The easiest thing to do there is get a replacement. Service guy should have already checked this but who knows if yours did..
    3) Your compressor has failed. Seek professional advice.
    4) The fan has failed. Seek professional advice or look at potential wiring issue.

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  • Thank you both, I will try all suggestions and report back my findings.
    – Aaron
    Commented May 23, 2013 at 1:51
  • I don't have owners manual it is a carrier tech 2000ss model 38tra, checked on line couldn't find where or how to adjust air flow will take apart Tom and clean coils.
    – Aaron
    Commented May 23, 2013 at 2:55
  • 1
    Watch out for #15 in that diagram. If you don't discharge the capacitor before working on the condenser unit, it can put you on your backside if you're not careful. Also, don't forget to pull the serviceman disconnect before opening up the condenser unit.
    – Tester101
    Commented May 23, 2013 at 12:22
  • Cleaned air flo coils outside notice white powder build up, possibly corrosion, when hosed with garden hose, philaments disinagrated, cleaned vents and intake vents, again and as of 2:20 pm, turned back on, will update in a couple hours, note it is periodically raining, and frost is building up.
    – Aaron
    Commented May 23, 2013 at 18:29
  • Hope that does the trick. Any buildup on those coils of any kind will degrade the performance. Do you know the model # for your air handler? (the big metal box inside your home) The installer usually leaves the manual sitting beside it or if you can get the model number the manual for that may be online and you can figure out the blower speed based on the dip switches. I found the manual for the 38TRA here Commented May 23, 2013 at 18:54

This is a classic sign of a plugged up evaporator coil. If the unit was run in a house with a lot of dust or pet hair some of the dust and dirt will get through the filter. One way to check it is to check the temp in the return air duct and then check it at the supply plenum, if it is greater than ten degrees it is a good indication of air blockage.

The other way is to remove the front of the supply plenum, usually there is another panel at the A coil (the evaporator coil). Take a look at the underside of it. if it is dirty then you can purchase cleaners that will foam away the dirt. Don't use any sharp object to scrape it. You can damage the coil, which is made of aluminum and is costly to fix!


Is the blower cage turning in the right direction? For some reason the blower motor changed direction? On my air handler the ecm module was replaced and instead of cw turn a ccw was installed. I found it out next day, everything was frozen inside the air handler cabinet than I found the motor was running the wrong direction.

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