I have an old A/C system and have replaced the old outside compressor with a Bryant reverse cycle heat pump (free and used). Apparently the compressor runs by default in the heat mode. I want to make it run only in the A/C mode. Can Anyone tell me how to do this. I am using the old thermonostate. Only 2 wires.

You will need to apply 24 volts to the reversing valve coil so it will activate and be in the cool mode.

I must ask, was it installed right,is it a package unit or a split system ,with the a/c-HP out side and the air handler on the inside? YOU SAID OLD OUTSIDE Compressor,making me think it's a split system if so was it vaccumed out and charged correctly ?

I agree with hvac1000. You need 24v on the " O " circuit at the heat pump to make it work. A quick fix is to jumper "Y" and "O" at the out side unit if your only using two wires.

I third that, it can be done very easily.

What do you use for 24 volts to get it back in cool mode

what do you use for 24 volts to get it back in cool mode

Step down transformer 120VAC>24VAC. Get them at any electrical supply, HD or Lowe's etc. Use thermostat wire for the 24VAC. If you are lucky, there is an extra pair in the main tstat line.