Push the A/C switch (Item 1) to the OFF position. Turn the fan switch (Item 2) to the High Speed position. Turn the temperature control (Item 3) [Figure 70-30-10] to the High A/C position, with the key switch OFF.
Start the excavator and run at high idle, for ten minutes.
Check the temperature of the heater hoses (Item 1) [Figure 70-30-11].
If the hoses are hot, the heater valve is leaking internally and needs to be replaced.