My chevy was running yesterday but, I don,t know

I couldn't find a heater hose diagram specific to the 1999 Chevrolet Venture with rear heat and air, but I can give you the general location of the heater hoses and how to identify which ones go to the rear heat. The heater hoses on a 1999 Chevy Venture are located on the passenger side of the engine compartment. There are two heater hoses, one that is hot and one that is cold. The hot heater hose will be connected to the heater core, which is located under the dashboard. The cold heater hose will be connected to the engine. To identify which heater hose goes to the rear heat, you can look for the hose that is connected to the heater core outlet that is labeled "Rear Heat." The other heater hose will be connected to the heater core outlet that is labeled "Heating Core Inlet." Once you have identified the heater hoses that go to the rear heat, you can reconnect them to the heater core. Be sure to use new clamps when you reconnect the hoses. Here are the steps on how to replace the heater hoses on a 1999 Chevy Venture with rear heat and air: Disconnect the negative battery cable. Drain the coolant from the radiator. Remove the heater hoses from the engine and heater core. Install the new heater hoses. Fill the cooling system with coolant. Reconnect the battery cable. Start the engine and check for leaks.

The 2 pipes that are coming through the firewall is your heater core. Simply put one hose on and the other hose to the other pipe. You can run water through the heater core either way. After you install the hoses, put a hose clamp on each one so the hoses don't fall off the pipes.

On my Chevy van the top connection on the heater core connects to the radiator and the bottom connection on the heater core connects to the engine.

Obisouvly a leak somewhere.Would start with upper and lower radiator hoses with vehicle running and at normal operating temp.This will allow the cooling system to build pressure,look for signs of wetness at hoses as well as heater core hoses from water pump to usually the firewall where they go into the passenger compartment to the heater core.

Should not make any difference as long as the hoses are the same inside diameter. one hose is input and the other is output. Should not make any difference which way the water flows thru the heater core.

The answer is no chevy couldn't care less about safty issues I could tell you storys there fuel systems.But getting back to your problem you say you don't have any leaks at least that you can see.Try this start vehicle and let it worm up to opperateing temp. Put your hands anound bolth haeter hoses going into and comeing out of the heater core if coolant is flowing through the core they bolth will be hot. If olny one is hot that means you have no flow. Some vehicles have whats called mixing valve it could be vacuum or cable opperated or even electricaly opperated but it will be in the heater lines before the coolant gets to the heater core to regulate you amount of hot coolant enters the core. It could also be a problem with the core being pluged or restriced however 06 is kind of new to have this problem because your coolant is good for at least 5 years but i would inspect the entire cooling system anywhy.Im vary formilar with systems but i haven't worked on a 2006 impala so i can't give you exact insturitions however what i have discribed is standard for all cooling systems and if coolant can't flow through the heater core you will have no heat hope this can help you

Replace heater core. You did not say if the leak was inside car or on outside firewall. Heater cores are cheap but to do it yourself it takes most of the day and you must be skinny.

First thing to do is check the antifreeze level in the radiator. An empty radiator won't always show a hot temperature gauge or make heat in the cab. If it's full, then the problem is probably your heater core. Judging by the year of your truck, thats where my money's at.

it makes no difference as long as you have coolant going it and out

Waterpump? The blades can erode away from age and old antifreeze. Or not enough airflow thru the radiator. Try blowing through the fins with an airhose to see if it is dirty or plugged.