Applicable Systems
Carrier ComfortLink Thermostat/Controller
Symptoms
Alarm E5 indicates a high discharge pressure condition. The controller detected discharge pressure above 400 psi (27.6 bar) and shut down the compressor to protect the system from excessive mechanical stress.
Possible Causes
- Condenser fan failure or insufficient airflow across condenser
- Dirty or blocked condenser coil reducing heat rejection
- Overcharge of refrigerant in the system
- Air or other non-condensables trapped in the system
Troubleshooting Steps
- Step 1: Check condenser fan operation and amperage draw
Replace any fans that are not running or drawing abnormal current - Step 2: Clean condenser coil with approved cleaner and high-pressure water
Verify coil is free of debris and fins are straight - Step 3: Connect manifold gauge set and compare readings with specification
If overcharged, recover excess refrigerant to proper charge - Step 4: If non-condensables are suspected, perform a system purge or full recovery and recharge
Evacuate system to below 500 microns before recharging
How to Reset
To reset E5: 1) Allow discharge pressure to drop below 350 psi. 2) Press Alarm Reset on controller. 3) The unit will restart after a delay if pressure remains within limits.
Common Replacement Parts
- HK25-0452: Condenser fan motor assembly (Verify correct rotation direction after installation)
- K10-2442: High-pressure switch, 400 psi cutout (Verify setpoint matches system specification)
Frequently Asked Questions
- Q: What is the normal discharge pressure range?
For R-404A systems at 35C (95F) ambient, normal discharge pressure is 250-350 psi (17-24 bar). Pressures consistently above 380 psi indicate a condenser problem.
- Q: Can I bypass the high-pressure switch to keep running?
Never bypass the high-pressure switch. This safety device prevents catastrophic system failure and potential safety hazards from overpressure.
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Source: Carrier Transicold Prelude Service Manual, Form 62-12788
Category: Refrigeration
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