agreed it is the wrong approach, although it's not actually 50W. 12V / 12ohms = 1A, therefore 12W. The 50W resistor is LR's way of making sure it will not burn out.

yes that's correct. You said you bypassed the relay (pins 30 & 5), after which the HEVAC engages the clutch properly ?? If yes, then it could be the relay is not pulling enough current. However if the compressor still only engages for a few seconds each time, you need to check the...

It does sound like early HEVAC behaviour, because when you bypass the relay it sees the higher clutch current draw ? Could also be a bad relay, so swap that for a new one first ?? Depending on ambient temperature, the compressor should be on for more than 1-2 seconds though, at least until the...

also test the relays

If you look in RAVE it's all explained. HEVAC enables the fans, but unless pressure-switch-2 engages (247psi) they will be off. The exception on petrol is when the engine gets really hot, the fans will also be turned on. The dual-pressure-switch only changes the fans from series to parallel...

I'm fairly sure one of my HEVAC is the early version, mainly because I had clutch gap issues causing intermittent operation. Both of them in my P38's and my spare all have heated seat buttons. Only real way to tell is to take the unit out & check the label.

Before you go that route, take the HEVAC out & check the part number to verify if that could be the issue. The tech bulletin for early P38 & HEVAC is attached & shows the resistor. You already have the relay installed, so do what Keith said & bridge it. That will prove if the dual pressure...

Fans are a separate issue to the compressor only engaging once. - Pressure Switch 2 is to turn on the fans either if pressure >>247psi, but the engine ECU will override if engine temperature gets too high. - Dual Pressure switch only turns them into fast mode is pressure >>305psi. Switch-2 has...

+1 on this. Remember a prev owner may have swapped the controller due to LCD issues, etc. Simply the early HEVAC will engage the clutch once, but not see enough current, so it thinks to clutch is faulty & disengages again until the next time the HEVAC is powered on.

The diagrams are all in RAVE.

Also has the HEVAC control unit been replaced with an early version ?? If it has, then it needs an extra resistor so the output drive transistor thinks it's powering the clutch direct.

+1 on first job is to sort the LH Blend motor. Remeber the book symbol comes on for any faults within the HEVAC system. Probably worth getting a set of AC gauges & check the pressures. Even if you never re-gas yourself, at least you then know if the system is within range. Plenty on...

There are no code for the dual-pressure switch. If the pressure is above 35psi it will be closed, so the HEVAC can engage the compressor. If the gas stays between 17psi & 305psi then it will remain closed & allow the HEVAC to control the compressor on-off as required. Note: the other half...

I have a couple that definitely have issues with solder joints on the wires into the PCB, although that could be PCB track issues. Was planning to replace the capacitor at same time. Will try your heat trick (but not too much heat) !!

I was digging this one for many days in spare time. Still cannot get the PCB out. Is there a trick ?