Should you be able to read 24vac between the red wire and any other colour wire?

That all depends on the type of thermostat and it's circuitry.
What type and brand of thermostat, and which system are you referring to ?

I wish I knew all those answers. It is a digital thermostat on a forced air gas type furnace installed in 2000. The thermostat has contacts marked RH, RC, W, Y, G. The red wire goes to RH and RC. The blower is permanently on. It can only be shut off by the switching off the furnace.

Can't get it to blow hot or cold. If you have any ideas I would relly appreciate it.

Thanks for answering.

Jim Menzies