Buick LeSabre
This line provides ground to the relay and is normally open (N-O) when the control unit (CU) is OFF, and is normally closed (N-C) for all other control functions. The OFF switch on the CU is "sticky." Several questions arise: 1) Can AC Delco CU part numbers 15-71886 or 15-71932 be substituted for part number 15-71887 (GM #16145214), if one is easier to find? All three units have the same mounting tabs and display the same push-buttons in a different configuration on the front. 2) Is the switch that controls ground to the blower speed relay an internal transistor? If so, which one? 3) There is hesitation to spend $250-500 for a replacement CU, even if one can be found. Is there an AC Delco electronics service center that can repair the unit, and where can it be found online? 4) If a reasonable replacement CU cannot be found, where can the control line to the blower speed relay be jumpered to a different ground to create a permanent ON signal to the blower resistor? Can it be jumpered to the known good ground line on the C2 connector that connects ground to the CU itself? The control line (ground) from the dashboard control unit to the blower speed relay is intermittent, which is suspected to be the failure point. This line applies a ground signal to the blower speed relay, which controls the blower. It is controlled by a switch on the control unit circuit board. It is unclear if the switch is a multi-pole switch hardwired to the bank of eight buttons on the control unit (with OFF being an open state and all other buttons being closed) or if it is a transistor connected to the seven front panel buttons that control AC/heat. Clarification is needed regarding whether this is a manual system, as the information indicates that the controller supplies voltage to the resistor and that the blower is directly grounded. Voltage is supplied to both the fan speed selector switch on the CU and the blower resistor through the blower speed relay. The control wire on the CU (C3-H) supplies ground to the relay, activating the solenoid and closing the switch to provide power through the resistor to the fan. Access to the control unit circuit board schematic is requested. If available, it should be uploaded. Alternatively, advice is sought on whether to jumper from C3-H (control) to C2-H (ground) to create a permanent ground condition for the blower speed relay. An under-dash toggle switch is also considered.
The circuit in question involves a control unit that manages the operation of a blower motor via a relay. The relay serves as an interface between the control unit and the blower motor, allowing for various operational states based on user input. When the control unit is OFF, the relay remains in a normally open state, preventing current flow to the blower motor. When any of the operational buttons are pressed, the control unit applies a ground signal to the relay, energizing it and allowing current to flow through to the blower motor.
The control unit's internal architecture may involve either mechanical switches or transistors to manage the ground signals. If mechanical switches are used, they may be configured in a multi-pole arrangement, where the OFF position is open (no current flow) and all other positions close the circuit, providing a ground signal. If transistors are employed, they would act as electronic switches, allowing current to flow when activated by the control unit.
For troubleshooting, if the ground signal to the blower speed relay is found to be intermittent, it may be beneficial to create a permanent ground connection. This could be achieved by jumpering the control wire (C3-H) directly to a known good ground (C2-H). This modification would bypass the control unit's switching mechanism, providing a continuous ground to the blower speed relay. However, it is advisable to incorporate an under-dash toggle switch to maintain control over the blower operation, allowing the user to manually disconnect the circuit when necessary.
In terms of replacement units, inquiries regarding compatibility among AC Delco part numbers should be directed to a qualified parts dealer or manufacturer. For repairs, contacting an authorized AC Delco service center is recommended, as they would have access to the necessary schematics and components for effective repairs. Access to the circuit board schematic would provide further insight into the internal workings of the control unit and assist in diagnosing potential issues with the ground signal.This line provides ground to that relay and is N-O when CU is OFF, and is N-C for all other control functions. The Off switch on the CU is "sticky" as I mentioned before. Several questions: 1) Can I substitute AC Delco CU p/n 15-71886 or p/n 15-71932 for p/n 15-71887 (GM #16145214), if one or the other is easier to find All three units have the same mounting tabs
and show the same push-buttons in a different configuration on the front. 2) Is the switch that controls ground to the blower speed relay an internal transistor If so, which one 3) I`m not inclined to want to spend $250-500 for a replacement CU, even if I can find one in the free world. Is there an AC Delco electronics service center that can repair the unit Where would I find it on-line 4) Barring finding a replacement CU at a reasonable price, where would I jumper the control line to the blower speed relay to a different ground to create a permanent ON signal to the blower resistor Can I jumper it to the ground line (known good) on the C2 connector that connects ground to the CU itself I think I did.
As I said above, the control line (ground) from the dashboard control unit to the blower speed relay is intermittent (95% sure this is the fail point). This line applies a ground signal to the blower speed relay which controls the blower. It is controlled by a switch of some kind on the control unit circuit board. I don`t know if the switch is a multi-pole switch that is hardwired to the bank of eight buttons on the control unit (with OFF being an open [no ground signal applied ~ relay not energized] and all other buttons being closed [ground signal applied ~ relay energized]), or it may be a transistor that has one leg wired to the seven front panel buttons that control AC/heat.
Do you know If this is a manual system my info shows that the controller is suppling voltage to the resister and the blower is dirrectly grounded so I need to know for sure what it is See attached circuit diagram. Voltage is supplied to both the fan speed selector switch on the CU and to the blower resistor through the blower speed relay.
The control wire on the CU (C3-H) supplies ground to the relay, which activates the solenoid and closes the switch to provide power through the resistor to the fan. Do you have access to the control unit circuit board schematic If so, could you upload it Alternately, would you advise a jumper from C3-H (control) to C2-H (ground) to create a permanent ground condition to the blower speed relay Note: I would include an under-dash toggle switch.
Oh ok yes I follow you now, I was not catching what you were saying. I do not have a schematic of the circuit board, you could only get that from the manufacturer. As for adding a toggle switch yes that should work. Ask-a-doc Web sites: If you`ve got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers. Justanswer. com. Traffic on JustAnswer rose 14 percent. and had nearly 400, 000 page views in 30 days. inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent. 🔗 External reference
The circuit in question involves a control unit that manages the operation of a blower motor via a relay. The relay serves as an interface between the control unit and the blower motor, allowing for various operational states based on user input. When the control unit is OFF, the relay remains in a normally open state, preventing current flow to the blower motor. When any of the operational buttons are pressed, the control unit applies a ground signal to the relay, energizing it and allowing current to flow through to the blower motor.
The control unit's internal architecture may involve either mechanical switches or transistors to manage the ground signals. If mechanical switches are used, they may be configured in a multi-pole arrangement, where the OFF position is open (no current flow) and all other positions close the circuit, providing a ground signal. If transistors are employed, they would act as electronic switches, allowing current to flow when activated by the control unit.
For troubleshooting, if the ground signal to the blower speed relay is found to be intermittent, it may be beneficial to create a permanent ground connection. This could be achieved by jumpering the control wire (C3-H) directly to a known good ground (C2-H). This modification would bypass the control unit's switching mechanism, providing a continuous ground to the blower speed relay. However, it is advisable to incorporate an under-dash toggle switch to maintain control over the blower operation, allowing the user to manually disconnect the circuit when necessary.
In terms of replacement units, inquiries regarding compatibility among AC Delco part numbers should be directed to a qualified parts dealer or manufacturer. For repairs, contacting an authorized AC Delco service center is recommended, as they would have access to the necessary schematics and components for effective repairs. Access to the circuit board schematic would provide further insight into the internal workings of the control unit and assist in diagnosing potential issues with the ground signal.This line provides ground to that relay and is N-O when CU is OFF, and is N-C for all other control functions. The Off switch on the CU is "sticky" as I mentioned before. Several questions: 1) Can I substitute AC Delco CU p/n 15-71886 or p/n 15-71932 for p/n 15-71887 (GM #16145214), if one or the other is easier to find All three units have the same mounting tabs
and show the same push-buttons in a different configuration on the front. 2) Is the switch that controls ground to the blower speed relay an internal transistor If so, which one 3) I`m not inclined to want to spend $250-500 for a replacement CU, even if I can find one in the free world. Is there an AC Delco electronics service center that can repair the unit Where would I find it on-line 4) Barring finding a replacement CU at a reasonable price, where would I jumper the control line to the blower speed relay to a different ground to create a permanent ON signal to the blower resistor Can I jumper it to the ground line (known good) on the C2 connector that connects ground to the CU itself I think I did.
As I said above, the control line (ground) from the dashboard control unit to the blower speed relay is intermittent (95% sure this is the fail point). This line applies a ground signal to the blower speed relay which controls the blower. It is controlled by a switch of some kind on the control unit circuit board. I don`t know if the switch is a multi-pole switch that is hardwired to the bank of eight buttons on the control unit (with OFF being an open [no ground signal applied ~ relay not energized] and all other buttons being closed [ground signal applied ~ relay energized]), or it may be a transistor that has one leg wired to the seven front panel buttons that control AC/heat.
Do you know If this is a manual system my info shows that the controller is suppling voltage to the resister and the blower is dirrectly grounded so I need to know for sure what it is See attached circuit diagram. Voltage is supplied to both the fan speed selector switch on the CU and to the blower resistor through the blower speed relay.
The control wire on the CU (C3-H) supplies ground to the relay, which activates the solenoid and closes the switch to provide power through the resistor to the fan. Do you have access to the control unit circuit board schematic If so, could you upload it Alternately, would you advise a jumper from C3-H (control) to C2-H (ground) to create a permanent ground condition to the blower speed relay Note: I would include an under-dash toggle switch.
Oh ok yes I follow you now, I was not catching what you were saying. I do not have a schematic of the circuit board, you could only get that from the manufacturer. As for adding a toggle switch yes that should work. Ask-a-doc Web sites: If you`ve got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers. Justanswer. com. Traffic on JustAnswer rose 14 percent. and had nearly 400, 000 page views in 30 days. inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent. 🔗 External reference
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