Hi Everyone, new to the forum. I have a 95 Yukon, 350 tbi. It's a new project I'm fixing up to use as a hunting truck. I have a couple of issues with it, and I'm looking for some suggestions.
Symptoms:
1. No Heat
2. Running cool (160 F)
What I've done so far:
1. First thing I did was pull the thermostat (195F thermostat) and tested it on the stove... it opens and closes as expected. I reinstalled the thermostat with a new seal.
2. Next I noticed that the vacuum line going from the little actuator clipped onto the evaporator to the heater control valve was disconnected. I reconnected it, and it still didn't work. I replaced the actuator, and it still didn't work. I ran the vacuum source line directly to the heater control valve, and it then opened the heater control valve... not sure what's going on with the actuator... what actually controls that actuator? Interior temp control? Interior fan control?
3. After making the heater control valve open up, I let the truck run for a while, and felt both heater hoses... the heater core inlet gets hot, and the outlet gets warm, but not as hot as the inlet line. Should they both be about the same temperature? Also, still no heat at this point. I disconnected the hoses and flushed the heater core... flow seams restricted, so I'm thinking I might need a heater core. I would expect some heat in the interior heater air, though even with restricted flow in heater core. Is that a fair assumption?
4. I checked the blend door actuator and it is reacting as the temperature control knob is turned.
5. None of the other gauges on the dash (oil pressure, fuel, volt meter, speedometer) are working properly, so I thought the temp gauge or temp sensor might be bad. Since none of the gauges are working, I bought and installed a set of mechanical gauges... temp shows 160 F.... I guess that gauge was actually working properly. Oh well. no loss.
6. I noticed that the fan speed increases as the engine speed increases, so I thought the fan clutch might be seized. I turned off the motor, and the fan moves with very little force required, but does not spin freely. How much resistance should it have?
So now what?
The engine is still running at 160, and there is no heat.
I'm thinking I might re-test the thermostat, with a thermometer in the pan, to see exactly what temp it opens at. Should it just start to open at 195 or should it start opening sooner, and reach full open condition at 195?
Thanks in advance!
Symptoms:
1. No Heat
2. Running cool (160 F)
What I've done so far:
1. First thing I did was pull the thermostat (195F thermostat) and tested it on the stove... it opens and closes as expected. I reinstalled the thermostat with a new seal.
2. Next I noticed that the vacuum line going from the little actuator clipped onto the evaporator to the heater control valve was disconnected. I reconnected it, and it still didn't work. I replaced the actuator, and it still didn't work. I ran the vacuum source line directly to the heater control valve, and it then opened the heater control valve... not sure what's going on with the actuator... what actually controls that actuator? Interior temp control? Interior fan control?
3. After making the heater control valve open up, I let the truck run for a while, and felt both heater hoses... the heater core inlet gets hot, and the outlet gets warm, but not as hot as the inlet line. Should they both be about the same temperature? Also, still no heat at this point. I disconnected the hoses and flushed the heater core... flow seams restricted, so I'm thinking I might need a heater core. I would expect some heat in the interior heater air, though even with restricted flow in heater core. Is that a fair assumption?
4. I checked the blend door actuator and it is reacting as the temperature control knob is turned.
5. None of the other gauges on the dash (oil pressure, fuel, volt meter, speedometer) are working properly, so I thought the temp gauge or temp sensor might be bad. Since none of the gauges are working, I bought and installed a set of mechanical gauges... temp shows 160 F.... I guess that gauge was actually working properly. Oh well. no loss.
6. I noticed that the fan speed increases as the engine speed increases, so I thought the fan clutch might be seized. I turned off the motor, and the fan moves with very little force required, but does not spin freely. How much resistance should it have?
So now what?
The engine is still running at 160, and there is no heat.
I'm thinking I might re-test the thermostat, with a thermometer in the pan, to see exactly what temp it opens at. Should it just start to open at 195 or should it start opening sooner, and reach full open condition at 195?
Thanks in advance!