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i have a 97 gmc jimmy 4.3 no heat check t-stat heater core vac line...
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epiphaknee
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Well I think you about covered the range of problems. You would check or replace the thermostat (make sure it is oriented properly, 195 degrees), flush the coolant, inspect the water pump (for leaks and strange noise), change the radiator cap and flush the heater core. You would determine whether you are topping off your coolant from time to time (indicator of a leak). Flush the heater core by disconnecting the heater hoses and apply a garden hose to both heater hoses. Any debris noted? This often times has a temporary improvement on generating heat.
Most likely, however, this is going to be the dreaded heater core. Typically the heater core will be leaking on the passenger side, under the carpet, but you will be able to smell the coolant. The temperature control door could be malfunctioning too. It is located right on the firewall, inside the vehicle, on the passenger side. It is electrical, if I recall correctly. However, it is probably not this.
There are excellent how to's on replacing the heater core on the Internet. Try s10forum.com.
Most likely, however, this is going to be the dreaded heater core. Typically the heater core will be leaking on the passenger side, under the carpet, but you will be able to smell the coolant. The temperature control door could be malfunctioning too. It is located right on the firewall, inside the vehicle, on the passenger side. It is electrical, if I recall correctly. However, it is probably not this.
There are excellent how to's on replacing the heater core on the Internet. Try s10forum.com.
epiphaknee
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So it sounds like the air flows out of the defrost but it is still not hot?
So now you know the defrost door is not openning and closing. It is just staying open. Defrost is the default position. So that is either a bad actuator (opens the defrost door and closes it), a pinched or compromised vacuum line or a bad mode control switch (the A/C-Heather control switch).
So you have two problems identified now. Defrost door stays open and no heat.
Regarding the defrost door. Do you hear any hissing? That is always a good indicator of a bad switch or compromised vacuum line. You would therefore determine if you have vacuum at the control switch, then inspect the vacuum lines and work your way to the actuator that opens and closes the door. Initially you would start at the vacuum ball under the hood and hope that some vacuum line in the engine compartment is bad and replace it. Any hissing under the hood, typically near the firewall?
That's a bitch, because the lines can only be accessed inside the vehicle from behind the dash. So you have to pull several panels to get to the point where you can tilt the dash back and see what you are doing. Not too bad, because your no hear problem is probably the heater core and you'll have to do this to access the heater core too.
The heater core can easily get clogged up and when that happens it can slowly or suddenly lose its ability to heat the vehicle. The flushing, noted above was designed to maybe rule that in or out.
You did not share with me whether you top off your coolant from time to time. Do you? That is the easy way to determine that you have a coolant leak somewhere. Then you just need to find it, typically by pressure testing the system.
So it's probably going to be a new heater core and maybe a mode control switch or a pinched or compromised vacuum hose.
So now you know the defrost door is not openning and closing. It is just staying open. Defrost is the default position. So that is either a bad actuator (opens the defrost door and closes it), a pinched or compromised vacuum line or a bad mode control switch (the A/C-Heather control switch).
So you have two problems identified now. Defrost door stays open and no heat.
Regarding the defrost door. Do you hear any hissing? That is always a good indicator of a bad switch or compromised vacuum line. You would therefore determine if you have vacuum at the control switch, then inspect the vacuum lines and work your way to the actuator that opens and closes the door. Initially you would start at the vacuum ball under the hood and hope that some vacuum line in the engine compartment is bad and replace it. Any hissing under the hood, typically near the firewall?
That's a bitch, because the lines can only be accessed inside the vehicle from behind the dash. So you have to pull several panels to get to the point where you can tilt the dash back and see what you are doing. Not too bad, because your no hear problem is probably the heater core and you'll have to do this to access the heater core too.
The heater core can easily get clogged up and when that happens it can slowly or suddenly lose its ability to heat the vehicle. The flushing, noted above was designed to maybe rule that in or out.
You did not share with me whether you top off your coolant from time to time. Do you? That is the easy way to determine that you have a coolant leak somewhere. Then you just need to find it, typically by pressure testing the system.
So it's probably going to be a new heater core and maybe a mode control switch or a pinched or compromised vacuum hose.