Replacing HVAC controller

Datatek said:

Suitably over complicated.
Need more facts, does the car have a relay fitted for the compressor clutch? Is the replacement HEVAC the late version that requires a relay?

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Hi
My car does not have a relay in pos RL3. It's a '97 4.6 HSE. The replacement panel is a JFC102550, the old one is probably a JFC102400 (to be confirmed upon removal). So, will I need to follow the diagram, or do I simply trigger a relay with the existing feed to the clutch and run a dedicated feed through the relay?

Thanks!
Henrik

Henrik97 said:

Hi
My car does not have a relay in pos RL3. It's a '97 4.6 HSE. The replacement panel is a JFC102550, the old one is probably a JFC102400 (to be confirmed upon removal). So, will I need to follow the diagram, or do I simply trigger a relay with the existing feed to the clutch and run a dedicated feed through the relay?

Thanks!
Henrik

Click to expand...

I see no reason why that should not work, however you MUST put a suppressor diode in line with the clutch feed to the relay coil or across the relay coil to stop back EMF damaging the HEVAC, obviously the correct diode polarity must be observed.

Datatek said:

I see no reason why that should not work, however you MUST put a suppressor diode in line with the clutch feed to the relay coil or across the relay coil to stop back EMF damaging the HEVAC, obviously the correct diode polarity must be observed.

Click to expand...

Thanks!
I was hoping to find a relay with built in flyback protection, but if not I will install a diode. So you agree that the resistor dummy load would not be needed when converting from early type to later type, only when going the opposite way?

H.

Henrik97 said:

Thanks!
I was hoping to find a relay with built in flyback protection, but if not I will install a diode. So you agree that the resistor dummy load would not be needed when converting from early type to later type, only when going the opposite way?

H.

Click to expand...

That is how i understand it.

Hi all,
Update: I removed the existing controller and found it was a JFC102550, with a build date a couple of years after the car rolled off the line. This would probably mean that if any modifications had been needed to make it work, they would have been done already. Anyway, that was my logic and I installed the replacement without any mods. Result? All good!
Correct outside temp displayed, book symbol gone and AC operating fine. The only thing that puzzles me is that my existing JFC102550 had defects that are typical of the earlier unit and the reason why LR recommends installing a 1025550. So it would seem that the later unit can be affected with the same bugs as the earlier one, only probably not quite so often....