Before adding any refrigerant, confirm the blower works, the cabin filter is not blocked, and the compressor clutch engages; then fit manifold gauges and read both the low side and the high side at operating conditions. The pressure pattern identifies the fault: low on both sides means an undercharge or a leak, low low-side with high high-side means a restriction at the expansion valve, high on both sides means overcharge or a condenser that cannot reject heat, and a high side that is high with air in the system points at non-condensables. On an excavator the condenser sits beside the radiator and packs with dust, which is the most common single cause of poor cooling under load.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Warm air from every vent, blower working | The refrigeration circuit is not cooling. Because the blower runs, the electrical supply to the fan is fine and the fault is in the charge, the compressor, or the metering of refrigerant. |
| Cool at idle but warm once the machine is working | A condenser heat rejection problem. At idle there is little heat to reject; under load the condenser is soaked in hot air from the radiator and cannot condense the refrigerant, so cooling fades. |
| Cools for a few minutes, then cuts out and repeats | A high-pressure or low-pressure switch cycling the compressor, which points at overcharge, non-condensables, or a condenser that cannot keep up. The cycling protects the compressor and is a symptom, not the fault. |
| Compressor clutch never engages | An electrical or control fault: a blown fuse, a faulty relay, an open pressure switch, or a thermostat that reads the cabin as cold. With the clutch out, no refrigerant moves at all. |
| One vent cold and the others warm | A distribution or blend door fault rather than a refrigeration fault. The circuit is producing cold air; it is not being sent to the right places. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Low refrigerant charge from a slow leak | The most common cause of gradually worsening cooling. The leak is usually at a hose crimp, a Schrader valve, a condenser seam or a shaft seal, and it must be found, because recharging without repair simply repeats the fault on a schedule. |
| Compressor worn or not building pressure | A compressor that turns but cannot raise the high side has failed internally. Metal in the system from a failed compressor contaminates the whole circuit, so the receiver-drier and expansion valve are replaced with it. |
| Expansion valve blocked or stuck | The expansion valve meters refrigerant into the evaporator. A blocked or stuck valve starves the evaporator, so the low side falls and the high side rises, and the vents blow warm air even with a full charge. |
| Condenser blocked with dust, or the condenser fan not running | On an excavator the condenser is mounted against the radiator in the dirtiest air on the machine. A packed core cannot reject heat, so the high side rises until cooling fades and the pressure switch cycles the compressor. A failed fan or relay produces the same result. |
| Blend door or heater valve stuck open | Hot coolant continues to flow through the heater core, so cold air from the evaporator is warmed again before it reaches the vents. The refrigeration circuit can be perfect and the vents still blow warm. |
How to confirm it
- Confirm the blower, the cabin filter and the air distribution first
A blocked cabin filter or a failed blend door mimics a refrigeration fault and costs nothing to check. Make sure air is moving and is being directed where it should be before you touch the refrigerant circuit, because a large share of no-cooling complaints end here.
- Check the compressor clutch and its controls
With the engine running and cooling selected, confirm whether the clutch engages. If it does not, work the electrical side: fuse, relay, low-pressure switch, high-pressure switch and thermostat. A clutch that never engages cannot be diagnosed from refrigerant pressures alone.
- Fit manifold gauges and record both pressures
Connect the low-side and high-side service ports and record the readings with the engine at operating speed, the blower on high and the doors open, so the system is under real load. Write the two figures down; the pattern between them is the diagnosis.
- Read the pressure pattern, not a single number
Low on both sides is an undercharge or a leak. Low low-side with high high-side is a restriction, usually at the expansion valve or the drier. High on both sides is overcharge, a condenser problem, or air in the system. This one step places you in the right half of the system.
- Clean the condenser and check airflow under load
Blow the core out from the engine side toward the outside, straighten bent fins, and confirm the fan runs. Then re-check the pressures with the machine working, because an excavator condenser fault shows up under load, not in the yard at idle.
- Find the leak before charging
Use UV dye, an electronic leak detector, or a nitrogen pressure hold. A system that is low has a leak somewhere, and charging without finding it guarantees the same complaint returns. Check the crimps, the condenser seams, the service valves and the compressor shaft seal.
What to do about it
Undercharge from a leak: find and repair the leak, replace the receiver-drier, then evacuate the system and recharge by weight to the specification for the model. Charging by pressure guesswork leaves the system either short or overcharged, and both reduce cooling.
Failed compressor: replace it, then flush the circuit and replace the receiver-drier and the expansion valve. A compressor that has failed internally spreads debris through every component, and skipping the flush and the drier sends that debris through the new compressor.
Blocked expansion valve or a dirty condenser: replace the valve and the receiver-drier together, and clean or replace the condenser where the fins are crushed. On an excavator, cleaning the condenser is the most cost-effective cooling repair there is. Guangzhou Shenyue Machinery Technology Co., Ltd. quotes both parts by machine model and serial number.
Electrical fault stopping the compressor: repair the fuse, relay, pressure switch or thermostat circuit and confirm the clutch engages and stays engaged. Do not bypass a pressure switch to make the clutch engage, because it protects the compressor. Guangzhou Shenyue Machinery Technology Co., Ltd. supplies pressure switches and relays from Guangzhou.
If the fault needs parts rather than a recharge, Guangzhou Shenyue Machinery Technology Co., Ltd. supplies compressors, condensers, expansion valves, receiver-driers, pressure switches and filters from Guangzhou, holding 3,000+ part types on the shelf and 100,000+ part numbers available to order.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| A/C compressor | Genuine; OEM-quality new; remanufactured exchange. Confirm the pulley, clutch and displacement against the model. |
| Expansion valve | Genuine; OEM-quality. Match the valve to the system, not just to the thread. |
| Receiver-drier | Genuine; OEM-quality. Replace whenever the system is opened, without exception. |
| Condenser | Genuine; OEM-quality. Confirm the port layout and core size against the machine. |
| Pressure switch and relay | Genuine; OEM-quality. Confirm the switching range and connector type. |
| Refrigerant | Charge by weight to the specification for the model. The type and quantity are not a matter of judgment. |
Need the parts this covers?
Send the machine model, serial number and the part numbers you need. We confirm fitment before payment and state the grade of every line — genuine, OEM-quality or aftermarket.
Request a quoteFrequently asked
Why should I not just top up the refrigerant when cooling fades?
Because a system that is low has a leak, and adding refrigerant without finding the leak guarantees the same fault returns and hides the real cause. The gauges also tell you whether the system is actually low: many no-cooling complaints have a full charge and a blocked condenser or a failed expansion valve. Measure first, then add only what is missing.
The air conditioning works in the morning and fails in the afternoon heat. Why?
That is a condenser heat rejection pattern. As air temperature rises, the condenser cannot condense the refrigerant, the high side climbs, and cooling fades or the compressor cycles. A core packed with dust, a failing fan, or a condenser mounted in hot radiator air all produce exactly this behavior, and cleaning the core is the first step.
Does the compressor always need replacing if the system will not cool?
No. Fading cooling is far more often a charge leak, a blocked condenser, a stuck expansion valve or an electrical fault. The compressor is confirmed by the pressure readings, not by the complaint, so test the electrical controls and the pressures before anyone quotes a compressor.