HVAC switchpack for a Cerbera
Discussion
I’m not sure if the above pictures have worked or not.
My cold fan, is getting between 6v and 9.6v, so not blowing on full power.
The HVAC switchpack appears to be 5v operated. On pin 4, when the cold button is pressed, I get an output of 1.5v, as I turn the dial, it creeps up to 2.5v That goes to the HVAC controller, which then gives me the 6v to 9.6v at the fan.
Pin 10 appears to be the 5v supply to the switchpack. If I bridge pin 10 to pin 4, I send 5v to the controller, and get the elusive 12v at the fan.
The potentiometer behind the switch seems to work ok, 0 ohms to 10k, as the dial is span.
It’s that little pot on the back of the boards that seems to restrict my outputs. Same for the hot fan too.
Has anyone had a crack at playing with one of these, yet ?
Better still, does anyone know a place that could fix/adapt it for me, please ?
I basically want a 1.5v to 5v variable output on pin 4
My cold fan, is getting between 6v and 9.6v, so not blowing on full power.
The HVAC switchpack appears to be 5v operated. On pin 4, when the cold button is pressed, I get an output of 1.5v, as I turn the dial, it creeps up to 2.5v That goes to the HVAC controller, which then gives me the 6v to 9.6v at the fan.
Pin 10 appears to be the 5v supply to the switchpack. If I bridge pin 10 to pin 4, I send 5v to the controller, and get the elusive 12v at the fan.
The potentiometer behind the switch seems to work ok, 0 ohms to 10k, as the dial is span.
It’s that little pot on the back of the boards that seems to restrict my outputs. Same for the hot fan too.
Has anyone had a crack at playing with one of these, yet ?
Better still, does anyone know a place that could fix/adapt it for me, please ?
I basically want a 1.5v to 5v variable output on pin 4
Edited by RUSSELLM on Tuesday 26th May 18:55
That looks like quite a simple analogue controller, the Chip is a Quad amplifier and I'm guessing is used to buffer and scale the output voltages from the two control pots to the HVAC. The two smaller trim pots probably only make a fine adjustment to the output levels. You could try to adjust them but I doubt it would give you the range you want.
All of those board components are generally reliable under normal operation so perhaps dirt and corrosion on the board / wiring connections are having an effect? You could gently clean the board and connector with Isopropryl Alcohol and a toothbrush. Sometimes the chip works itself lose from the socket due to heat cycling and that could affect performance. Gently prise out the chip from both ends with a small screwdriver and re-insert it, that sometimes works. Be careful doing this, the legs are quite fragile and bend easily. You could change the chip while you're at it, just in case one section has failed, it's an LM324N and they're readily available from RS Components or Farnell for about £0.60. Either way, make sure you insert it in the same orientation.
I might be able to rescale the output but I'd be wary of doing this, if the voltage drop is being caused elsewhere in the system and it suddenly fixes itself you may end up with a fan that runs flat out all the time.
All of those board components are generally reliable under normal operation so perhaps dirt and corrosion on the board / wiring connections are having an effect? You could gently clean the board and connector with Isopropryl Alcohol and a toothbrush. Sometimes the chip works itself lose from the socket due to heat cycling and that could affect performance. Gently prise out the chip from both ends with a small screwdriver and re-insert it, that sometimes works. Be careful doing this, the legs are quite fragile and bend easily. You could change the chip while you're at it, just in case one section has failed, it's an LM324N and they're readily available from RS Components or Farnell for about £0.60. Either way, make sure you insert it in the same orientation.
I might be able to rescale the output but I'd be wary of doing this, if the voltage drop is being caused elsewhere in the system and it suddenly fixes itself you may end up with a fan that runs flat out all the time.
Thanks for the response.
I’ve discussed it on the Cerbera forum, and I’m starting to think that the switchpack’s output is normal.
I’ve got a few things to test this week. I’m going to replace the inline connectors to the fans. Check their current draw, direct from a battery, to see if they’re tired and pulling too much. Check the Ignition and ground supplies to the controller.
If that’s ok, and I suspect it will be, I’m happy to take the chance, if you think you can get me 1.5v to 5v outputs, for Two outputs (Hot and Cold)
The HVAC controller sends a permanent 12v to the fans, and varies the ground. So the easy fix is to put a hard ground to the fan, via a switch, for full pelt situations. But I’d rather get it working properly off the dials.
I’ve discussed it on the Cerbera forum, and I’m starting to think that the switchpack’s output is normal.
I’ve got a few things to test this week. I’m going to replace the inline connectors to the fans. Check their current draw, direct from a battery, to see if they’re tired and pulling too much. Check the Ignition and ground supplies to the controller.
If that’s ok, and I suspect it will be, I’m happy to take the chance, if you think you can get me 1.5v to 5v outputs, for Two outputs (Hot and Cold)
The HVAC controller sends a permanent 12v to the fans, and varies the ground. So the easy fix is to put a hard ground to the fan, via a switch, for full pelt situations. But I’d rather get it working properly off the dials.
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