I just bought a 1996 gmc jimmy. The vehicle runs fine but the temperature gauge never moves. There is air coming out of the AC blower but it's always cold. The fan works fine. I was wondering why my temperature gauge wasn't working and what I could do to fix it.. Also when I put it in drive and hold my foot down on the brake there is a terrible knocking. When I put it in park the knocking goes away. What could that be?
Check temp sensor in head
SOURCE: 2000 GMC Sierra 5.3 Litre, won't blow hot air
I experienced the same head ache. First attempt was to replace the thrmostat and after taking it apart I realized that there was nothing wrong with it. I then removed the plastic cover/panel located under the dash board on the passenger's side. (only a few 4-5 smalls screws) Removal will enable you to see the on/off switch/gate moving/rotating as you turn the knob to hot or cold positions, on the control panel. If that switch/gate seems to work ok, then the trouble is within the heater core. Many mechanincs suggested that I replace the heater core. A very expensive proposition.
I checked the heater core supply/intake hose and found it hot to the touch, while the return hose was nearly cold. It was definitely a heater core blockage. I removed both ends (supply and return) hose connections/clamps. They are located near the fire wall in the engine compartment. A special tool is very helpful to remove those clamps easily and to replace them as well. It can be done the old fashion way but this tool was a life saver and reduced work time to just minutes. (Tool is $70.00 bucks at auto parts store,so I borrowed mine from a mechanic/friend)
I then hooked up a garden hose to the return end of the heater core and reversed the flow of coolant/water through the heater core. My truck is a Sierra 2000 and I refuse to see how a heater core could get clogged up with clear coolant alone. To my surprise a flat piece of rubber about the size of a quarter blew out of it and the flow of water became unobstructed. I reconected the ends of the hoses to the heater core, replaced the lost antifreeze & everything returned back to normal. No money spent for something most mechanics suggested I replace control valves/switches ($280.00) replace heater core ($500.00) etc etc. I am glad I was curageous enough to tackle this myself and save a few pennies. Good luck, and I hope this will work for you.
SOURCE: 2004 Odyssey, heat and A/C do not work unless van in motion
Since warm air eventually comes out when the vehicle is in motion, you may have an air mix door that is stuck in fresh or is somehow blocking warm air from the heater core.
To see if the air mix control motor is bad, you need to retrieve your Diagnostic trouble codes (DTC's) from the heater control panel. To run the diagnostic function, do the following:
1. Turn the ignition switch ON (II).
2. Turn the fan switch OFF.
3. Press the recirc control button to select Recirc (recirc light on.)
4. Press and hold the recirc button to select Fresh (recirc light off) and continue to hold the button down until the recirc light comes on for two seconds and then goes off.
5. If the system is okay, the recirc light stays off.
6. If there is a problem, the recirc light blinks the DTC to indicate the trouble. One blink=a problem in the air mix control motor circuit. Two blinks=problem in the mode control motor circuit
Three blinks=problem in evaporator temp sensor circuit.
7. Turn the ignition switch off to cancel the self diagnosis function. Run the diagnostic again after repairs are complete.
Note: the air mix control motor has a rod which connects to a plastic link. The link controls the mix doors and also connects to the heater control water valve via a cable. The air mix motor may check okay, but if the link is broken then you will still have problems. the motor is on the bottom of the heater unit in the front passenger's foot well.
SOURCE: No heat in my 2000 GMC Sonoma w/AC. Engine warms
that year / series of GM sonoma and s-10 where famous for having clogged heater cores - is temp of hoses going in and out the same ? if not try to flush out ther core, if they are, ck to see if the hot water valve is woking, and finally operation of the doors inside the heater box itself
Testimonial: "Success! Reverse flushing heater core fixed problem. Less than a tablespoon of dirt came out yet it gave no heat. Now works great. Thanks much. Jim."
SOURCE: Heat/Temperature gauge
the temp sensor sounds like it maybe bad and not responding the way it should.they are cheap 10 - 20 dollars and easy to replace.
SOURCE: after running for 20 minutes or more , the heater
Hello: Check the coolant level, fill up the reservoir and run truck, if reservoir shows low again fill it back up. If reservoir was low/empty the check for leaks. Do this before you replace thermostat. The heater core would not create this kind of condition.
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