Service the air path before the refrigerant circuit. Most excavator cabs that stop cooling have a blocked fresh-air or recirculation filter, an evaporator face matted with dust, or a condensate drain that is plugged and keeping the box wet. Replace both filter elements, clean the evaporator with a low-pressure cleaner working along the fins, clear and flush the drain, and check blower current against specification. Only when airflow is restored and the vents still blow warm should the refrigerant charge be measured. Regassing a cab with a blocked filter cools nothing and hides a leak that will return within a season.
What you will notice
| Symptom | What it usually points to |
|---|---|
| Cool at first, warm after twenty minutes | Evaporator icing from restricted airflow or a faulty thermostat. Check filters and the evaporator face before the refrigerant. |
| Airflow weak at every vent but the air is cold | Filter or blower. Temperature is right and volume is not, which is an air-path fault. |
| Musty smell and fogging on the glass | A wet evaporator box. Clear the condensate drain and clean the case. |
| Cooling fades when the machine is working hard | Condenser airflow or fan drive. Check the condenser face and the fan, not the cab. |
| Dust in the cab with a filter newly fitted | A missing or badly seated element, or a cracked case. Verify the seal, not the filter. |
Most likely causes
| Cause | How to confirm it |
|---|---|
| Blocked fresh-air or recirculation filter | The usual cause. Most cabs have two elements and only one gets changed. |
| Evaporator fins matted with dust and pollen | Air passes around the blockage rather than through it. Clean along the fins, never across them. |
| Condensate drain plugged or routed uphill | Water stays in the box, the evaporator stays wet, and the smell follows within weeks. |
| Blower motor drawing high current | A failing motor or a dry bearing. Measure current; a motor above specification is about to stop. |
| Refrigerant loss from a joint or the condenser | Only relevant after airflow is proven. Look for oil staining at joints before adding anything. |
Service intervals, and what each task protects
| Interval | Task and reason |
|---|---|
| 250 h | Clean the outer element and confirm the drain runs free. |
| 500 h | Replace the fresh-air element; inspect the evaporator through the access panel. |
| 1000 h | Replace the recirculation element; clean the evaporator; flush the drain. |
| Seasonal | Check blower current and vent temperature; clean the condenser face with the radiator. |
| After a dusty job | Clean both elements and the evaporator; dust that reaches the evaporator stays there. |
How to confirm it
- Locate both elements before ordering anything
Most cabs have a fresh-air element behind the outer panel and a recirculation element inside the cab, and they are different part numbers. Order against the cab serial number; a filter that fits the housing but seals badly passes dust straight to the evaporator.
- Clean the case and the evaporator face
Remove the blower resistor first, work with low-pressure water or air along the fins, and let the case dry before refitting. High pressure bends fins flat and turns a cleanable evaporator into a replacement.
- Clear and flush the drain
Pour clean water into the box and watch it leave under the cab. A drain that runs slowly is a drain that will block. Re-route any hose that was pushed uphill during an earlier repair.
- Measure blower current and vent temperature
Compare blower current against specification at each speed, and read vent temperature with the doors closed and the engine at working speed. These two numbers, before and after, are the proof the service worked.
- Only then evaluate the refrigerant circuit
With airflow correct, measure suction and discharge pressures against ambient temperature. Guangzhou Shenyue Machinery Technology Co., Ltd. supplies cab filters, blower motors, evaporator and heater cores, expansion valves and condensate parts for common excavator cabs, matched to the cab serial number. Stock is held as 3,000+ part types on the shelf, with 100,000+ part numbers available to order.
What to do about it
Replace a pleated element, do not wash it Washing collapses the pleats and leaves media that cannot hold dust, and a damp element grows the smell you were trying to remove. Foam and mesh elements can be cleaned if they are intact and still seal.
If the box stays wet after the drain is cleared, find where the water enters A cracked case or a missing grommet lets rain and wash water in, and no amount of drain cleaning will keep up with it. Seal the case before replacing anything else.
If airflow is correct and the vents are still warm, measure the charge Read suction and discharge pressures against ambient, and check that the condenser fan and the compressor clutch behave. Add refrigerant only after a leak has been found, or the same gas leaves again within a season.
If the blower draws high current, replace the motor rather than the resistor A resistor is usually the casualty, not the cause. A motor that has been drawing high current for a while has already damaged the connector, so inspect the plug as well.
Parts you may need, by grade
| Part | Grades commonly quoted |
|---|---|
| Cab fresh-air filter | Genuine; OEM-quality; aftermarket. Media grade and seal dimensions stated. |
| Recirculation filter | Genuine; OEM-quality; aftermarket. A different part number from the fresh-air element. |
| Blower motor | Genuine; OEM-quality. Connector and speed configuration confirmed before dispatch. |
| Expansion valve and receiver-drier | Genuine; OEM-quality. Seals supplied with the valve. |
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 does the cab cool better in the morning than in the afternoon?
Because the condenser has to reject more heat into hotter air, and a partly blocked evaporator loses capacity as the load rises. It is not usually a refrigerant charge that changes with the clock. Clean the condenser face and the evaporator, then compare vent temperature at the same ambient in the morning and the afternoon; the difference tells you whether the air path or the circuit is short of capacity.
Can I just clean the cabin filter and put it back?
For a flat foam or mesh element, yes, if it is intact and still seals. For a pleated paper element, no: washing leaves it unable to hold dust and a damp element produces the smell you were trying to remove. Replace pleated elements and record the hours on the service sheet.
Water drips on the ground under the cab. Is that a leak?
That is the drain working. Water under the cab in humid weather is condensate and it is supposed to leave the box. A cab with no drip and a wet evaporator has a blocked drain, which is the condition that produces fogging, smell and eventually a corroded case.