Carrier Air Conditioner: Two-stage unit not changing stages – Carrier 24ANB/25HNB/25HCB6
Two-stage unit not changing stages - Carrier 24ANB/25HNB/25HCB6 on a Carrier air conditioner: Unit runs but capacity does not seem to change between low and high stage.
Applies to: 24ANB1, 24ANB7, 25HNB6, 25HNB9, 25HCB6, CH17
Common causes of two-stage unit not changing stages - carrier 24anb/25hnb/25hcb6
- Unloader solenoid not getting 24 V DC
- Solenoid plug without internal rectifier
- Open or grounded unloader coil
- Control or thermostat not calling Y2
How to fix two-stage unit not changing stages - carrier 24anb/25hnb/25hcb6: step by step
- Watch suction pressure: it should fall roughly 3-10 percent going to high stage; do not judge by liquid pressure.
- Compressor amps should rise 20-45 percent in high stage.
- Cycle low/high at 30 s or longer intervals and read amps 5 s after the change; at least 20 percent change is expected.
- No change: unplug the solenoid plug and check for 24 V DC while high stage is called.
- Voltage good: measure the coil; about 330 or 1640 ohms is normal - open or grounded means compressor replacement.
- Only use a solenoid plug with the built-in rectifier.
If the unit shows an error code, look it up: Carrier Air Conditioner codes
Models
Carrier 2-stage 24ANB/25HNB
24ANB12424ANB13624ANB14824ANB16024ANB72424ANB73624ANB74824ANB760
Carrier Infinity 19VS 24VNA9
24VNA924VNA91324VNA92424VNA92524VNA93624VNA93724VNA94824VNA94924VNA960
Source: Carrier Residential AC & HP Application Guideline and Service Manual 24-25-9SM (text export), Unloader Test Procedure. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.