Make:  Trane

Model or Series:  4TWR

Type:  Heat Pump

Problem Description:  Contactor won't energize

Observed Symptoms:  24Volts on "Y" but never starts contactor

Solution:  Found bad high pressure switch

Additional Information:  

• Checked for and had 24V at Yellow wire on defrost board plug
• On the defrost board plug jumped Yellow wire to Yellow/Black & still no contactor
• Unplugged defrost board plug & checked continuity from Yellow/Black to contactor - found open circuit.
• Checked continuity of low pressure & high pressure switches
• Found open high pressure switch