I have a 1979 olds cutlass. The heater doesnt blow on low or high. But the two middle levels it blows air. Tried a good relay and that didnt fix it. tried a new heater speed switch in the dash. that didnt fix it. Im seriously stumped on this one.
heater control problem
- Thread starter 79cutlasssalon442
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Low and Med are controlled by the switch, and by the resistor pack in the heater box. High is controlled by the relay. Since you have a new switch, and High works, then the only other part of the system is the resistor pack. Could be that the low resistor is burnt out. Easy to pull out and check.
OK, they could be two separate problems. High gets it's power directly from the starter, through a 4 pin connector , to the relay. Make sure the relay is seeing 12V on the large red wire. If not, trace it back to the 4 pin connector- it is usually down near the passenger side header. Hint- the green wires from the accumulator low pressure switch run through this same connector. This is a known problem area- connection gets hot and fries the connector.
For the Low, I would still check the resistor pack. It has several resistors to provide different speeds. Since you have two of those speeds, it's likely that one of the resistors is bad. They are just wound coils, so it should be easy to see if they are bad. Could also be a bad connection at the resistor pack, so check that connector as well for dirt, etc.
For the Low, I would still check the resistor pack. It has several resistors to provide different speeds. Since you have two of those speeds, it's likely that one of the resistors is bad. They are just wound coils, so it should be easy to see if they are bad. Could also be a bad connection at the resistor pack, so check that connector as well for dirt, etc.
Checked the red wire at the relay. It has 12.35 volts. Tried multiple grounding points and they all read about the same.darbysan said:
OK, so you are down to the resistor pack. It is used to reduce the voltage for the lower speeds, and also to pass the High Speed current through ( bypass). It's located underneath the connector- 2 screws IIRC. Pull it and take a look.
Nothing out of the ordinary. I have an extra one and they look the same. No breaking in the coils. No corrosion anywhere. Put the other one in and it didnt help. Where is the relay supposed to ground to? Or is that included with the 4 pin connector? Just a thought.darbysan said:
The relay shares the ground with the blower motor ( spliced inside the harness), so if the blower is working on any speed, then the relay is getting it's ground. You've checked the relay and it's power ( and ground via the motor). You've replaced the switch, so we expect that it is also good. You've checked the resistor pack, and that is good, so the only thing left is a connection somewhere.
You can place the switch in the high speed position, and see if you are getting 12V at the relay on the Orange wire. If so, then the switch is commanding the relay to go to the high side. If 12v is there, then you should have 12V on the purple wire to the fan. No voltage indicates a bad/stuck relay ( Since you have already confirmed 12V on the red wire to the relay).
If you place the switch in the low position, you should have 12V on the Brn wire going to the resistor pack, and some voltage ( lower than 12v) on the purple wire at the motor
If you place the switch in Med1 position, you should have 12V on the Tan wire at the resistor pack, and some voltage ( lower than 12v) on the purple wire at the motor
If you place the switch in the Med2 position, you should have 12v on the Lt Blue wire at the resistor pack, and some voltage ( lower than 12v) on the purple wire at the motor
Low, Med1, and Med2 power all comes out of the resistor pack on the Dk BLue wire, which goes to the relay. The relay bypasses it's 12V red input on the lower speeds, and flows through the reduced voltage from the resistor pack to the blower on the same purple wire.
HTH
You can place the switch in the high speed position, and see if you are getting 12V at the relay on the Orange wire. If so, then the switch is commanding the relay to go to the high side. If 12v is there, then you should have 12V on the purple wire to the fan. No voltage indicates a bad/stuck relay ( Since you have already confirmed 12V on the red wire to the relay).
If you place the switch in the low position, you should have 12V on the Brn wire going to the resistor pack, and some voltage ( lower than 12v) on the purple wire at the motor
If you place the switch in Med1 position, you should have 12V on the Tan wire at the resistor pack, and some voltage ( lower than 12v) on the purple wire at the motor
If you place the switch in the Med2 position, you should have 12v on the Lt Blue wire at the resistor pack, and some voltage ( lower than 12v) on the purple wire at the motor
Low, Med1, and Med2 power all comes out of the resistor pack on the Dk BLue wire, which goes to the relay. The relay bypasses it's 12V red input on the lower speeds, and flows through the reduced voltage from the resistor pack to the blower on the same purple wire.
HTH
Thanks for all that. I checked the four pin connector again and tried a different relay. The high works again. And the low came back. But now the purple wire doesnt connect well the to blower motor. And when i was going to work the high just shut off. its 10:30 so in the morning im gonna take another look and figure out whats going on.darbysan said:
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