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Brian HVAC Guy
Brian HVAC Guy, HVAC Technician
Category: HVAC
Satisfied Customers: 921
Experience:  I have been an HVAC/R mechanic/technician for 30+ years.
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Carrier heat pump question: AC stops blowing cool air...notice

Customer Question

Carrier heat pump question: AC stops blowing cool air...notice that the compressor is not running. Turn off power to compressor, set all thermostats to off and unplug molex connector to circuit board in compressor cabinet. When the molex connector is unplugged immediately the compressor sounds like it is releasing pressure. I wait a few minutes, plug everything back in and the unit will start working. Not sure how to determine what the issue is...
Submitted: 2 years ago.
Category: HVAC
Customer: replied 2 years ago.
(Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Brian HVAC Guy replied 2 years ago.
Hi I'm Brian and I'm here to help! The noise you hear when you unplug the molex connector is the reversing valve de-energizing and the system pressures equalizing as a result. That is normal if the unit was in cooling and hasn't been off very long. When you have the problem and you say "notice that the compressor is not running" do you mean the entire outdoor unit (compressor and outdoor fan motor) is not running, or do you mean the outdoor fan motor continues to run but you can tell from the sound that the compressor is not running? Let me know that and we'll go from there
Customer: replied 2 years ago.
fan and compressor not running
Expert:  Brian HVAC Guy replied 2 years ago.
Thanks for that info. The most likely cause for this is one of the unit safeties has tripped. Your unit may have a high refrigerant pressure switch (HPS), a low refrigerant pressure switch (LPS) and a discharge temperature switch (DTS) installed in it. If any one of those safeties has tripped it would give those symptoms. A LPS trip is caused by low refrigerant, a dirty filter, a dirty indoor coil or a low indoor airflow from an indoor blower or duct issue. A HPS trip is usually caused by either a failing outdoor fan motor or capacitor or a dirty outdoor coil. A DTS trip can be caused by the same issues as a HPS trip. The first things you should do is look at your filter and indoor/outdoor coils to ensure they are clean and clean them if they're not. This is the most common cause for your symptom. Please reply if you have further questions about this. Otherwise, please remember to rate positively before you leave. Bonuses are welcome and always appreciated! Thanks, -Brian

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