Air con / heater system - function advice please?

[lordivanhoe]

Hey all, wondering if anyone has an answer to this query..?

OK, so, happy days, my air con (having been checked over and regassed earlier this summer) now works.
Unfortunately, some as-yet-to-be-determined fault means that my radiator fans don't respond to any 'automatic' signal(s) from anywhere in the car.  Including turning on the air con.
When I got the car, the radiator fan was set to 'permanently on' by means of a connection directly across the otterstat switch (I understand this happens a fair bit?).
A new otterstat hadn't solved the problem.
Up until now, no problem; I installed a manual switch in the cabin and have installed temp sensors in the engine and gauges in the cabin; I keep an eye on those, and if the engine temp warrants it, I turn the rad fans on.  Just means a bit of extra alertness required..!
Of course, this means I also have to turn the rad fans on when the air con is on (again, doesn't come on automatically).
Something obviously amiss somewhere in the rad fan control circuit, but sorting that's a job (on the list!) for another day..

(Sorry, finally getting to the question here!)
Now, the air con/ heater master control knob goes through various 'modes' as you turn it.  IIRC, it's 'max' air con, then 'norm' air con, then 'bi-level', then 'vent', then 'heater' and finally 'defrost'.
Clearly the air con is expected to be ON and I NEED to have the rad fans running for the first two modes.

But (and here, at last, is the question): what other modes is the Air Con system supposed to be nominally 'ON'?  (or in other words, in what other modes does the air con normally activate, in a fully functioning system?)
I have not dared to use anything other than the first two 'air con' modes up 'til this point, 'cos obviously if the air con switches on but the rad fans aren't also on then I could boil (?) or otherwise bu99er up my air con; conversely, I don't want to put the rad fans on unnecessarily if in fact the system is in a mode in which the air con would be 'off'.

I guess a related question is: what does the system actually do in 'bi-level' and 'vent' modes..?
For completeness, my presumption is that warm air is blown into (respectively) the car or up onto the windscreen in the 'heater' or 'defrost' modes.
(but is the air con also on, of course..?)

Look forward to any nuggets of wisdom!!

Cheers aye,

Ivan..

[Rissy]

On the AC panel, the following energise the compressor to circulate your gases:

MAX (same as NORM but with hot water valve behind engine closing off hot water to the heater matrix in the cabin)
NORM (same as MAX but with hot water valve behind engine allowing hot water to the heater matrix in the cabin)
BI-LEVEL (same as NORM, but air flaps splitting hot air to lower footwell and colder air towards face vents (early AC panels show RED line above BLUE line, which is wrong. Should be BLUE line above RED line for cold up top and warm down below))

On all other modes, the compressor doesn't spin up.

VENT opens the outside air vent to allow fresh air to enter the cabin.
HEATER doesn't open the outside air vent, so circulating cabin air only.
Both these modes direct air towards centre face vents, footwell vents and door vents
DEFROST biases the air flow towards the windscreen vents. This is the only mode to do this. Air is still passed to other vents, but will be weaker.

The fan relay has two input sources:

1. Otterstat. This is based on engine temperature only
2. Parallel feed which clutches in your compressor. With this feed the compressor fires up, as do the cooling fans. These will both cycle on and off according to the low and high pressure switches.

People putting in an Otterstat bypass switch allows for two manual override scenarios:

1. Suspected failed operation of Otterstat at the point where the engine is getting too hot. Force fans on from override switch instead.
2. When in an active AC mode, close override switch to hold fans on all the time and only allow compressor to cycle on and off with the low and high pressure switches (due to high current draw every time fans kick in)

Fault finding for any of these actions not taking place will involve close inspection of the wiring against the wiring diagram, and using a multimeter to determine the flow of current at any time of action from the surrounding equipment.

I hope that helps.

[lordivanhoe]

(27 Nov 2023, 10:44)Rissy Wrote: On the AC panel, the following energise the compressor to circulate your gases:

MAX (same as NORM but with hot water valve behind engine closing off hot water to the heater matrix in the cabin)
NORM (same as MAX but with hot water valve behind engine allowing hot water to the heater matrix in the cabin)
BI-LEVEL (same as NORM, but air flaps splitting hot air to lower footwell and colder air towards face vents (early AC panels show RED line above BLUE line, which is wrong.  Should be BLUE line above RED line for cold up top and warm down below))

On all other modes, the compressor doesn't spin up.

VENT opens the outside air vent to allow fresh air to enter the cabin.
HEATER doesn't open the outside air vent, so circulating cabin air only.
Both these modes direct air towards centre face vents, footwell vents and door vents
DEFROST biases the air flow towards the windscreen vents.  This is the only mode to do this.  Air is still passed to other vents, but will be weaker.

The fan relay has two input sources:

1.  Otterstat.  This is based on engine temperature only
2.  Parallel feed which clutches in your compressor.  With this feed the compressor fires up, as do the cooling fans.  These will both cycle on and off according to the low and high pressure switches.

People putting in an Otterstat bypass switch allows for two manual override scenarios:

1.  Suspected failed operation of Otterstat at the point where the engine is getting too hot.  Force fans on from override switch instead.
2.  When in an active AC mode, close override switch to hold fans on all the time and only allow compressor to cycle on and off with the low and high pressure switches (due to high current draw every time fans kick in)

Fault finding for any of these actions not taking place will involve close inspection of the wiring against the wiring diagram, and using a multimeter to determine the flow of current at any time of action from the surrounding equipment.

I hope that helps.

Hey, Rissy - thanks!
That seems pretty comprehensive!!  Brilliant, cheers, that should keep me safe and gives me something to check out when I eventually get round to working out what's going on with these fans.
Awesome.
Cheers!
Ivan.