High Discharge Pressure Compressor Shutdown
The THERMO-KING-10 (Thermo King) diesel fault code means: High Discharge Pressure Compressor Shutdown. This is a critical severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $50-$150 DIY for a condenser coil cleaning service and condenser fan inspection. Refrigerant system diagnosis, recharge, or high-pressure switch replacement by a certified reefer technician typically runs $200-$600 depending on labor rates and refrigerant costs.
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Common Symptoms
- Unit shuts down and the Smart Reefer 4 (SR-4) display shows Alarm Code 10
- Box temperature rises after shutdown because the refrigeration system is no longer running
- Unit may attempt to restart and immediately trip again on the same code
- Condenser fan is audibly running at full speed but unit still shuts down
- High-pressure cutout switch has tripped and you can hear the compressor cycle off abruptly
- Alarm light is active on the SR-4 panel and unit is in a locked-out or check-mode state
- Condenser coil feels unusually hot to the touch even shortly after shutdown
Probable Causes (Ranked by Likelihood)
- Dirty, clogged, or physically blocked condenser coil restricting airflow and causing heat buildup on the discharge side Very Likely
- Condenser fan motor failed, seized, or running backwards, reducing airflow across the coil Very Likely
- Refrigerant system overcharged with excess refrigerant, raising head pressure above safe limits Likely
- Non-condensable gases (air or nitrogen) in the refrigerant circuit pushing discharge pressure up Likely
- Defective or stuck-open liquid line solenoid or expansion valve causing refrigerant flood-back and elevated head pressure Possible
- High ambient temperature conditions combined with marginal condenser performance pushing system over the limit Possible
- Faulty high-pressure cutout switch sending a false trip signal even when actual pressure is within range Less Likely
Step-by-Step Diagnostic Procedure
Start with a visual inspection of the condenser coil from both sides. Look for debris, dirt, road grime, bugs, or physical damage blocking airflow. Even a partially blocked coil can push discharge pressure past the trip point on a hot day. Clean the coil with low-pressure water or compressed air from the inside out.
Check the condenser fan blade and motor while the unit is OFF. Spin the fan blade by hand. It should turn freely with no grinding or resistance. A seized or dragging fan motor will cut airflow dramatically.
Power the unit back on and watch the condenser fan immediately after startup. Confirm the blade is spinning in the correct direction, pulling air through the coil and exhausting out. A backwards-running fan is a common result of a miswired fan motor replacement.
Clear the alarm on the SR-4 panel (navigate to the Alarm Menu, acknowledge Alarm 10), then restart the unit in AUTO mode. Watch the unit run and check how quickly it trips again. A fast re-trip (under 2-3 minutes) with a clean coil and working fan points toward refrigerant charge or a stuck valve issue.
If you have manifold gauges, check head pressure while the unit is running. For R-404A systems at typical ambient temperatures, normal operating head pressure runs roughly 200-300 PSI. Pressures consistently above 350-400 PSI at moderate ambient confirm either overcharge or non-condensable gases. This step requires refrigeration gauges and EPA 608 certification to handle refrigerant.
Inspect the area around the condenser for restricted airflow from the installation itself. On nose-mount trailer units, check that the condenser discharge duct or grille is not blocked by tarps, loading dock equipment, or cargo overhang.
If the coil is clean, the fan checks out, and head pressure is within normal range when you verify with gauges, suspect the high-pressure cutout switch itself. A failed switch can send a false trip. Replacing the switch requires refrigeration system know-how. Call a certified reefer tech if you reach this point without a clear cause.
Frequently Asked Questions
What does Thermo King Alarm Code 10 mean?
Alarm Code 10 means the pressure on the discharge side of the compressor, the high-pressure side of the refrigerant circuit, climbed above the safe operating limit. The unit shut the compressor down automatically to protect it from damage. The most common reason is a dirty condenser coil or a failed condenser fan.
Can the reefer unit still run with Alarm Code 10 active?
Not in normal operation. The compressor is shut down, so the unit cannot maintain temperature. You can clear the alarm on the SR-4 panel and attempt a restart, but if the root cause is not fixed, it will trip again quickly. Your load is at risk if you cannot get the unit running. Address the cause before loading perishables.
How much does it cost to fix Alarm Code 10?
If it is a dirty condenser coil, a good cleaning costs very little, maybe $20-$50 in supplies if you do it yourself with a water hose and coil cleaner. A condenser fan motor replacement runs $150-$400 in parts depending on the model, plus labor if you use a shop. If the issue is refrigerant overcharge, non-condensables, or a faulty high-pressure switch, expect $200-$600 at a certified reefer service shop.
Will my reefer unit protect my load if Alarm Code 10 keeps coming back?
No. Every time the unit trips on Code 10, it stops cooling. If the unit is cycling on and off repeatedly, your load temperature will drift up between trips. Do not rely on a unit that is actively tripping on Code 10 to protect temperature-sensitive freight. Get the cause diagnosed and repaired before the next load.
Sources
This page is built from documented references. Verify against your own service info before repair work.