I have an older Trane heat pump (about 16 years old). The air handler is in the attic. It has started pulsing on and off like a heart beat. I can hear a click from the air handler when it does this. When this is happening the unit outside is also pulsing and the outside fan is starting and stopping. It's a rhythmic pulse (on and off every second.) Sometimes it does it when I first turn it on, or it starts after it has been running awile. It seems to be getting worse. What could it be.

Thanks Jeff

Wonder if a short in control wiring, or shorted coil on contactor. Loading down voltage to coil, releasing, going on, conducting(loading down) and repeating. See if you can measure
24 volts from transformer and see if it "Pulses"?
Also Measure 240 Volts, and see that it remains High, An amprobe can show if a load on the 240 volts side is drawing so much that the 24 volts also drop, dropping out relays or contactors.

In addition to what Stratmando said you may be low on refrigerant and cycling on a low pressure control, good luck, Mike

I have an older Trane heat pump (about 16 years old). The air handler is in the attic. It has started pulsing on and off like a heart beat. I can hear a click from the air handler when it does this. When this is happening the unit outside is also pulsing and the outside fan is starting and stopping. Its a rythmic pulse (on and off every second.) Sometimes it does it when I first turn it on, or it starts after it has been running awile. It seems to be getting worse. What could it be.

Thanks Jeff
Thanks guys. I guess Ill have to call a repairman.

Does it do it on heat, cool , or both? Don't Pay someone yet.

Does it do it on heat, cool , or both? Don't Pay someone yet.

I have not tried it on the cooling. Ill try it today sometime.

Jeff

Does it do it on heat, cool , or both? Don't Pay someone yet.

I switched it to the cool side and it immediately started clicking on and off. The air handler fan stays running but the unit is clicking or switching on and off. Sound like a solinoid clicking.