I got hardly any heat coming from a warmed up 92 SC400 motor. I pulled the horizontal heater hose connecting the heater control valve and got no flow when I started the engine. Is this normal? I put a garden hose into the coolant reservoir and turned it on and got water coming out the hose. I then took the vacuum line off the servo and jumped it to the vacuum pod to force it to open and forced water into the inlet (?) of the heater valve (the top fitting facing the driver side) and it blew water out the hose that I just took off it. I suspect its a complete loop. My question is what direction should I be backflushing it from, the top fitting or the bottom fitting? Bottom fitting requires the valve to be removed if Im not flushing through the valve. It has a strange crimp style hose clamp on the bottom. I did this to my 2002 Silverado and got a massive amount of crap to come out after about 30 seconds of pressurizing it (completely plugged with rust) and I got instant heat after that but uncovered a leak that took 3 rounds of stop leak to seal, finally sealing it with a teaspoon of ground pepper! It still works great and want to back flush this SC one now. The electric servo is working: I can pull a vacuum on one side and then turn the heater control to HOT and the vacuum will release. I think I proved my heater valve is functional too by pulling a vacuum on the pod and the actuator rod will move and will allow water to come out of top fitting. What is the direction of flow?

 

Try filling the heater core w/ CLR cleaner & let it sit for a 1/2 hour & then flush it out.

https://clrbrands.com/Products/CLR-H...d-Rust-Remover