This article gives simple first step diagnostics if your air conditioner or heat pump (in cooling mode) seems to run normally but the air it blows out is warm when it should be cool.

These are steps that can be taken by a building owner or occupant before calling an HVAC repair technician.

Page top photo: an indoor air handler or "blower unit" in a building attic, supported on 2x4's set into a condensate overflow drip pan. Notice that the cover is off?

The author trained as an HVACR repair technician and worked for three decades as an air conditioning & heat pump system inspector and repairman.

Fix an A/C or Heat Pump Unit that Blows Warm Air when in Cooling Mode

First let's be sure we've identified the cooling problem correctly:

1. If the air coming out of your air conditioning system supply registers has good flow but the output air temperature is not cool enough, continue below
   
   at AIR CONDITIONER's SUPPLY AIR IS NOT COOL ENOUGH - your are on the right page - below on this page we'll give a couple of easy things that you should check before calling your air conditioning service technician.
2. If the air flow coming out of your air supply registers is weak or none, a different and more appropriate diagnostic procedure to follow begins
   
   at Step 2: CHECK THE INDOOR AIR HANDLER UNIT and continues at
   
   at Step 3: WEAK AIR FLOW 1: CHECK THE AIR CONDITIONING /HEAT PUMP AIR FILTER(S)
3. If you have a different problem with your air conditioner go to our starting point
   
   at DIAGNOSTIC GUIDE A/C or HEAT PUMP 

...

Air Conditioner Air Flow is OK but Supply Air is Warm not Cool

While the most common cause of warm air out of an air conditioner is loss of refrigerant, the problem could be as simple as an improper setting on the controls for your cooling system.

Step 1: check the following:

• Your room thermostat is calling for cooling - it's in COOL mode, not OFF and not HEAT
• At the thermostat, the temperature is set to below the actual room temperature, and that
• You can feel air coming out of the supply air registers (so we know the air handler blower fan is working)

  Step 2: check for common causes of warm air coming out of the system supply duct registers, in order of probability.

  If the air conditioner or heat pump runs but in cooling mode the air supplied is too warm, there are several things that will cause warm air discharge from the supply registers of an air conditioning system or from a heat pump system in cooling mode including the following:

  • The compressor/condenser is not running at all.
    
    First check that electricity is turned on to your outdoor compressor/condenser unit. (A pair of these is shown in our photo above).
    
    Remember that there will be at least two power switches: the circuit breaker or fuse in your electrical panel (for the circuit powering the outdoor unit) and a service switch right at or close to the outdoor compressor unit.
    
    If you are not sure where these switches are to be found, then see
    
    ELECTRIC PANEL INSPECTION - find your electrical panel and check the breaker or fuse powering the compressor/condenser, then check the outdoor
    
    COMPRESSOR DISCONNECT SWITCH.
    
    Once we know the unit has electrical power and if you've observed that the outdoor unit is not running at all, and if we're sure that indoors the blower door and condensate overflow switch are not keeping the system OFF
    
    then see COMPRESSOR / CONDENSER DIAGNOSTICS
  • The compressor runs but refrigerant has been lost due to a leak
    
    see REFRIGERANT GASES & PIPING - home
    
    and GAUGE, REFRIGERATION PRESSURE TEST
  • The compressor runs, refrigerant charge is OK but the refrigerant metering device or TEV is jammed
    
    see Step 7: REFRIGERANT PRESSURE & TEMPERATURE CHECKS TO DIAGNOSE LOST COOLING CAPACITY below.

  If both indoor air handler and outdoor compressor are running and there is good air flow but the air is not cool, you need help from a service technician.

  S/he will check for problems such as lost refrigerant or a stuck refrigerant metering control (thermostatic expansion valve or TEV)

  GAUGE, REFRIGERATION PRESSURE TEST - how to check refrigerant levels

  THERMOSTATIC EXPANSION VALVE TEV INSTALL, DIAGNOSE, REPAIR - check for a stuck TEV that prevents cooling or heating

   

Schematic above showing a heat pump in "summer mode" or cooling mode is provided courtesy of Carson Dunlop Associates, a Toronto home inspection and education company.

If the steps above haven't solved your air conditioning trouble, continue with steps 1 through 9 given below at CONTINUE READING or RECOMMENDED ARTICLES.

...

...

Continue reading at DIAGNOSTIC DETAILS A/C or HEAT PUMP, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see AIR CONDITIONER BLOWS WARM AIR FAQs for questions & answers about condensate pump installation, inspection, troubleshooting, & repair and that were posted originally on this page

Or see these

Recommended Articles

• AIR CONDITIONING & HEAT PUMP SYSTEMS - home
• AIR CONDITIONING CHECKLIST FOR LOST COOLING
  • AIR CONDITIONING SYSTEM OR HEAT PUMP IS NOT RUNNING AT ALL - follow steps 1-9 just below
  • AIR CONDITIONER/HEAT PUMP IS RUNNING BUT COOL AIR IS NOT BEING DELIVERED
  • Step 1: CHECK THE OUTSIDE COMPRESSOR-CONDENSER UNIT
  • Step 2: CHECK THE INDOOR AIR HANDLER UNIT
  • Step 3: WEAK AIR FLOW 1: CHECK THE AIR CONDITIONING /HEAT PUMP AIR FILTER(S)
  • Step 4: WEAK AIR FLOW 2: NEXT CHECK THE SYSTEM DUCTWORK & AIR SUPPLY REGISTERS
  • Step 5: NO AIR FLOW AT ALL: CHECK THE INDOOR AIR HANDLER BLOWER FAN ASSEMBLY
  • Step 6: AIR FLOW IS OK BUT AIR IS NOT COOL
  • Step 7: REFRIGERANT PRESSURE & TEMPERATURE CHECKS TO DIAGNOSE LOST COOLING CAPACITY
  • Step 8: AIR CONDITIONER OR HEAT PUMP RUNS BUT MAKES STRANGE NOISES
  • Step 9: CALL YOUR HVAC SERVICE TECHNICIAN
• AIR HANDLER UNIT SWITCHES - find the blower unit power switch
• COMPRESSOR CONDENSER CONTROLS, SWITCHES - find the outdoor compressor/condenser switch
• DIAGNOSTIC GUIDE A/C or HEAT PUMP  - higher level diagnostics
• DIAGNOSTIC DETAILS A/C or HEAT PUMP - detailed diagnostic procedures
• In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
  
  CONTINUE READING or RECOMMENDED ARTICLES.

Suggested citation for this web page

AIR CONDITIONER BLOWS WARM AIR at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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