View Full Version : 98 Isuzu Hombre - No Heat

01-19-2008, 08:28 PM
I am not getting any heat to the passenger compartment of my truck. . . The engine heats up like normal but then cools back down to about 100 to 125 Deg. (According the the temperature gauge). I have replaced the thermostat but that did nothing for the issue. When I was under the hood, I noticed a vacuum hose broken so I also replaced that. When I am driving around 45 miles an hour, I have nothing but cold air through the vents. Once I reach 55 to 60, the heat starts working, but as soon as I am off of the interstate hwy., and in stop and go traffic, the heat stops working again.

I can't find anything in the Haynes Manual about the vacuum lines or an issue like this. Any help would be greatly appreciated.

01-21-2008, 04:06 PM
iresq4free - The HVAC controls uses vacuum to open and close the system. Opening and closing the blend door or directing air flow through the registers. In the engine compartment look for the heater hoses as the come up to the firewall. You may have a heater control valve in one of the hoses. It is either controlled by a cable or vacuum line. Make sure the valve opens and closes by moving the arm back and forth. If a vacuum line is off the system will not work properly.

01-22-2008, 02:34 AM
I didn't find a vacuum hose or control valve in either hose exiting the fire wall, but I did notice both were cool to the touch. One hose goes into where the thermostat housing is on top of the engine and the other hose goes into the same housing as the bottom raditator hose that is on the bottom of the engine. That housing looks like a thermostat housing as well. Could this be the control valve or a 2nd thermostat. If so, what is this called? The manual only talks about one thermostat and very little about the heater components. Many thanks!!

01-22-2008, 02:47 PM
iresq4free - There is only one thermostat. How long ago did you replace the t-stat. It sounds like the t-stat (thermostat) is stuck open.

01-23-2008, 12:03 PM
It was less than a month ago. I tested the old t-stat which was the origional one and it wasn't bad, but since I had it out I replaced it anyhow. I checked all hoses last night after driving for about an hour. I found the top and bottom radiator hoses warm and the heater hoses cold.

01-23-2008, 02:33 PM
What about the lower hose, is it getting hot. Are both heater hoses cold (end to end)?