what would cause my rear heater to only blow cold? 1994 4runner.

 

What type vehicle?

I imagine either your lines aren't getting hot fluid from the engine or you got a bad t-stat...does the front blow heat?

On my 85 the front/rear heat are all plumbed into the same lines off the engine bay. Follow your rear heater lines back and see if they are getting warm when the temp gauge gets up hot enough where you should have heat.

Good luck.

 

my front heater works great, back heater has no heat at all

 

I would guess either blocked line to the rear, or the control valve is stuck shut.

 

Turn it on and let it go for about 15 min. The first time I used mine it was cold too, but eventually got hot. It takes a while for the coolant to work it's way back there I guess.