I have a 2004 Nissan Quest, Problem— No Heat (defrost or Cabin) when initial start up and Idle. Only when driven up to highway speeds does the heat work correctly (Then heat works great). I have replaced the thermostat(No difference). I have removed the upper heater pump which has a 12 volt motor and Magnetic drive pump and the motor runs fine and pump end works great. I am thinking that ther is a sensor and or a relay the turns the heater pump on at startup and this is not functioning, does this sounf like the problem? If not do you have any ideas??
There might air trapped in the cooling system. Try this.
Get the engine up to operating temperature. With the the engine idling slightly loosen the upper radiator hose clamp. Take a flat bladed screwdriver and slip this between the upper radiator hose and the hose neck on the radiator. Allow the engine to idle until all the air is purged out of the cooling system. Retighten the hose clamp.
I’m not seeing what the problem is.
When you first start the car, the coolant is cold (ambient air temp), and the engine will take a while to heat up the coolant to the point where you will be able to feel it.
Now, if you are saying that after you get off the highway when the heat was working fine, and now are stopped at the first light, and the heat slowly vanishes, then yes, you have air in your cooling system, and need to do a specific air bleeding procedure to get all of it out.
Thanks for the Interest,
The problem is not when I am on the highway but when the car is in the driveway and it is cold out and I want to defrost the window before I go anywhere the heat will not come into the heater core to warm the car or defrost the window until I drive down the road and bring up the rpms to overcome the fact that the booster pump located in the engine compartment on the firewall above the engine does not run, I pulled it out and tested it was OK but is not powered when idleing as it should, that is why I am thinking that there is a sending unit somewhere that tells this pump to turn on initially to get heat fast to the heater core then turns off when you are going down the road as if it did not the motor wouls surely wear out after a long trip being a brush type DC motor, I hope this makes snse to you, Thanks, Don
Thank you so much for this tidbit of information. I had this problem with my best and your solution worked for me!