Outdoor air temperature sensor fault.
Homeowner part this code names: AC coil cleaner.
Search on AmazonOpens an Amazon search for that name. Check the size against your manual. As an Amazon Associate I earn from qualifying purchases.
Carrier 53 is an outdoor air temperature sensor fault on the 25VNA8 / 24VNA9. Count 5 short flashes and 3 long flashes. Causes are an unplugged or damaged harness, a damaged sensor, or a damaged outdoor control. If that sensor fails, the manual says defrost is started from coil temperature and time instead. It is not a charge code. Code 55 is the coil temperature sensor.
Likely causes
- Sensor harness not connected to the AOC control
- Broken or loose harness wire
- Broken or damaged sensor
- Hardware damage to the AOC control
Safe checks for 53
- A failed outdoor air thermistor changes defrost: the manual says defrost is then initiated from coil temperature and time
- Technicianconfirm the plug on the AOC, check harness continuity against the resistance chart, and replace the AOC if the control hardware is damaged
Capacitors can hold a charge after the power is off. Safety terms.
When to call a pro
Call a licensed HVAC technician. Code 53 is a sensor circuit. Do not add refrigerant to make a heat pump heat.
Find a Carrier dealer (official locator, opens in a new tab) ↗Email me this fix
We save your email and this page. Nothing is emailed. We'll only use your email for this request.
Request a filter and maintenance reminder
We save your email, this page, and the interval you pick. Nothing is emailed. We'll only use your email for this request.
Parts & tools for this fix
Taken from this code's causes or steps. A search link opens Amazon results and does not confirm a fit. Check the model number in the manual.
AC and heat pump coil cleaning supplies: guide
In this code: A failed outdoor air thermistor changes defrost: the manual says defrost is then initiated from coil temperature and time
See the guide for what to look for when buying one.
Multimeter for appliance and HVAC diagnosis: guide
Technician step in this code: confirm the plug on the AOC, check harness continuity against the resistance chart, and replace the AOC if the control hardware is damaged
This one is for a technician to test or replace, so we only explain it and do not link to buy it.