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George H.
George H., ASE Certified Technician
Category: Chevy
Satisfied Customers: 18308
Experience:  GM Tech ASE Master Tech 15+ years
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Hose..heater core..the engine block/heater control valve

Customer Question

I need a diagram showing the hose connections between the heater core/heater control valve and the engine block/heater control valve. My heater control valve is vacuume operated w/ four ports (two large and two each entering and leaving). The vehicle is a 1999 Chevy suburban K1500 5.7L w/ the rear air conditioning package. This means that there is a rear heater core. I appear to have three heater core hoses comming out of the fire wall and the odd number is XXXXX me a bit. A diagram of the hose routing would be of a great help. It also appears that the previous owner re-routed the hoses to bypass the rear heater core, but I can't fix the jerrey rigged situation until I know what it looked like originally. Help!!
Submitted: 6 years ago.
Category: Chevy
Expert:  George H. replied 6 years ago.

Hello I will help you with your question,


I don't know how much this will help but I see you posted your question some time ago and do not have an answer yet.


These are the diagrams that I have available and it does show the location of two of the hoses to the water valve




Here are the three hoses you see coming from the firewall




The Aux outlet hose is shown here




Let me know if this is enough for you. If it is not I will OPT OUT in the hope that another expert can be of assistance to you. Just let me know what I should do





Customer: replied 6 years ago.
Can I get a legend for the first diagram? Also, I need a diagram for the location/connection of the hoses to the actual heater control valve. But, these are the best that I have seen so far.
Expert:  George H. replied 6 years ago.

Here is the info for the first diagram





  1. Drain the engine coolant. Refer to Draining and Filling Cooling System in Engine Cooling.
  2. Remove the hose clamps from the outlet pipe (6) and from the inlet pipe (5).
  3. Remove the heater inlet pipe (5) and the outlet pipe (6) from the bypass valves (4).
  4. Remove the bolts (3) that retain the valves to the heater assembly.
  5. Remove the bypass valves (4) from the heater assembly.


  1. Install the bypass valves (4) to the heater assembly. NOTE : Refer to Fastener Notice in Cautions and Notices.
  2. Install the bolts that retain the valves (4) to the heater assembly. Tighten Tighten the bolts to 4 N.m (35 lb in) .
  3. Install the heater inlet pipe (5) and the outlet pipe (6) to the bypass valves.
  4. Install the hose clamps.
  5. Fill the cooling system. Refer to Draining and Filling Cooling System in Engine Cooling.
  6. Ensure that no leaks exist in the cooling system.


I am unsure what you mean by the "actual control valve" Do you mean the control head in the dash?