85k100rt
06-24-2010, 01:52 PM
The lock sensor, found on some E32 750il vehicles serves two functions. 1) It disables the compressor clutch in the event the compressor begins to seize by comparing engine speed with compressor speed.
2) It disables the compressor clutch if the coolant temperature exceeds a predetermined level, for example when climbing a long grade in hot weather.
The Break device, found on other E32 Models and on some 750il's converted to use R134 refrigerant in the US, eliminates the compressor speed comparison but retains the ability to disable the compressor if it detects excessive coolant temperature.
The IHKA blends hot air flowing through the heater core with cold air flowing through the evaporator to obtain its calculated output air temperature.
Both of these control modules are directly connected to the coolant temperature signal from the sensor that is used to drive the temperature gauge on the instrument panel.
An intermittent fault in either of these control modules related to the coolant temp (it's an analog circuit) can result in the cycling of the air temperature coming through the vehicles climate contol vents. This happens because the control module is intermittently improperly disabling the air conditiong compressor clutch.
In my case, over a period of approximately 6 months, the output air temperature cycled from hot to cold only for a period of time following a maintenance that required coolant to be removed and replenished. Eventually, the system returned to normal operation and worked as designed. Troubleshooting the IHKA proved both expensive and fruitless.
Two weeks ago, I began experiencing a problem with the temperature gauge. It was intermittently reading lower than normal coolant temperature even though the engine had been running for some time and should have been at the correct temperature. I suspected a thermostat that was sticking open and replaced it. This also proved fruitless, and the temperature gauge continued its intermittently false indications. Both the temperature sensor and the break device on my r134 converted 750il were replaced and all systems are back to working as designed (Yipee!, Yahoo!). I strongly suspect that, as the break device fault progressed, it adversely affected the coolant temp sensors output and this resulted in an incorrect indication on my temperature gauge. It may be that the fault actually caused the temp sensor to fail. On 1989 and 1990 750il models, the cycling of IHKA output air temperature can be resolved by removing the compressor control relay and inserting a jumper between the black/red wire and either of the grn/blu/yellow wires at the socket. This will keep your compressor running at all times, effectively crippling the lock sensor/break devices's ability and the IHKA control to turn off the compressor clutch. On other E32 models, this jumper must be added such that a hot in run or start (switched) 12v source is used. Otherwise, your clutch will be energized even with the key in "off" position. At any rate, the jumper should be used only until the root cause of the problem is corrected.
I have offered this information only as a result of my own experience and the recognition that others have experienced difficult to troubleshoot symptoms similar to my own. There may be other issues that can cause the same symptoms so please remember that YMMV.
Best Regards,
Bob
Please disregard for 5 series models.
2) It disables the compressor clutch if the coolant temperature exceeds a predetermined level, for example when climbing a long grade in hot weather.
The Break device, found on other E32 Models and on some 750il's converted to use R134 refrigerant in the US, eliminates the compressor speed comparison but retains the ability to disable the compressor if it detects excessive coolant temperature.
The IHKA blends hot air flowing through the heater core with cold air flowing through the evaporator to obtain its calculated output air temperature.
Both of these control modules are directly connected to the coolant temperature signal from the sensor that is used to drive the temperature gauge on the instrument panel.
An intermittent fault in either of these control modules related to the coolant temp (it's an analog circuit) can result in the cycling of the air temperature coming through the vehicles climate contol vents. This happens because the control module is intermittently improperly disabling the air conditiong compressor clutch.
In my case, over a period of approximately 6 months, the output air temperature cycled from hot to cold only for a period of time following a maintenance that required coolant to be removed and replenished. Eventually, the system returned to normal operation and worked as designed. Troubleshooting the IHKA proved both expensive and fruitless.
Two weeks ago, I began experiencing a problem with the temperature gauge. It was intermittently reading lower than normal coolant temperature even though the engine had been running for some time and should have been at the correct temperature. I suspected a thermostat that was sticking open and replaced it. This also proved fruitless, and the temperature gauge continued its intermittently false indications. Both the temperature sensor and the break device on my r134 converted 750il were replaced and all systems are back to working as designed (Yipee!, Yahoo!). I strongly suspect that, as the break device fault progressed, it adversely affected the coolant temp sensors output and this resulted in an incorrect indication on my temperature gauge. It may be that the fault actually caused the temp sensor to fail. On 1989 and 1990 750il models, the cycling of IHKA output air temperature can be resolved by removing the compressor control relay and inserting a jumper between the black/red wire and either of the grn/blu/yellow wires at the socket. This will keep your compressor running at all times, effectively crippling the lock sensor/break devices's ability and the IHKA control to turn off the compressor clutch. On other E32 models, this jumper must be added such that a hot in run or start (switched) 12v source is used. Otherwise, your clutch will be energized even with the key in "off" position. At any rate, the jumper should be used only until the root cause of the problem is corrected.
I have offered this information only as a result of my own experience and the recognition that others have experienced difficult to troubleshoot symptoms similar to my own. There may be other issues that can cause the same symptoms so please remember that YMMV.
Best Regards,
Bob
Please disregard for 5 series models.