Manual Override Switch for A/C Compressor/Radiator Fan

[Syncro Jael]

Here is the scenario:

It is 95°-100° ambient.

The A/C compressor is running and the condenser is HOT.

The Van is climbing a long, long, steep grade and the engine is working hard building heat, now shifted down to 3rd gear and going around 40-50mph, so the ram air is less.

Everything is great until the thermo switch see's that radiator temp is now at 102°c or 215°f and turns on the high speed fan and also cuts off the A/C compressor. Within minutes the cooling system begins to recover, turns the high speed fan off, and A/C compressor back on. But the interior of the van has now heated up due to the lack of A/C. So now it needs to work harder to cool the interior back off again. I also have this happen when off-road on slow trails keeping the windows closed so dirt and dust does not enter the van.

I would like to either turn the High Speed Fan on manually, without the relay triggering the compressor to turn off, or make a switch to keep the compressor running and closely watch to see if the fan can cool down the engine cooling system.

But I would prefer to keep the failsafe system working so that if the radiator still does hit the 102°c limit it will work as VW engineered.

My thought is to run a 50amp relay to switch the fan on high speed and bypass all the resistors and relays that are on the hot side of the fan.

Or to simply make a switch that will keep the compressor from kicking off.

"again wiring schematics are not in my bag of tricks"

Bentley 97.141

Can any of the electrical guru's lend a hand and show me what is the best way to make this happen? If the high speed fan would come on sooner I believe it can keep the cooling system in check and not play the on/off game so much. I checked the other threads and nobody had mentioned the A/C compressor as part of wiring the radiator fan toggle switch.
_________________
1987 Syncro Westfalia Hightop - NAHT
Subaru EJ25 Forged Frankenmotor, Triple Knob.
Jael = (Mountain Goat)

[djkeev]

Did it, I simply ran two wires to the A/C compressor area and fed the 12v through a dash switch.
I used an extra defrost switch mounted below the 4 Way switch, replaced the blank filler.
I got a roll of P-Touch tape, clear with white letters and labeled it.


My intent was to enable use of the Rear fans withoout the compressor running.

Dave
_________________
Stop Dead Photo Links how to post photos

Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[Wildthings]

You could use a 50+ amp switch or relay to apply power to the RED 6.0 wire attached to the 87/8 pin on the Radiator Cool Fan Relay, 3rd Stage. This would allow the system to work normally when the added switch (or relay) was open and not cut off the compressor when the added switch (or relay) was closed, yet the compressor would still cut off if the fan switch sensed the temps were too high.

[fxr]

A DPDT (double pole double throw) switch will do the job.

One pole goes across the rad high temp switch, wired NO (normally open).
The other pole goes where you've marked in blue, wired NC (normally closed).

One way, the system is left alone, the other way the fan will run at high speed and won't stop the AC compressor.
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[Syncro Jael]

[Howesight]

For the electrical system, I agree that the solution posted above by FXR will work nicely. In fact, I like the idea of manually switching on the highest fan speed for crawling instead of the on-off cycling.

I am curious, though, Jael, as to whether you used a parallel-flow condenser on your rig?

I am asking because in roughly similar conditions, my rig has only gone on to the 2nd or "mid" speed on the rad fan and I have used a large (24" x 16" )aftermarket condenser. I also carefully sealed the condenser to the radiator with weather strip so that the rad fan works more efficiently.

That highest speed on the rad fan is really noisy, so I wonder if it might be useful to have a "speed 2.5" by using a very low impedance resistor. Considering the draw, it should still flow through the 50Amp circuit and fusible link.
_________________
'86 Syncro Westy SVX

[Syncro Jael]

[Howesight]

You could tap into that 50 amp circuit, but I don't recommend it. Instead, use a DPDT switch to control the rad fan high speed relay. That's the relay right beside the 50 amp fusible link.
_________________
'86 Syncro Westy SVX

[Wildthings]

[Syncro Jael]

I am still unclear on how to wire a DPDT switch across the relay.

With six legs on the switch it doesn't compute in my mind what is happening.
_________________
1987 Syncro Westfalia Hightop - NAHT
Subaru EJ25 Forged Frankenmotor, Triple Knob.
Jael = (Mountain Goat)

[kourt]

Howdy,

As I understand it (for 3-speed fans):

Stage 1: operates when radiator reaches a certain temperature (usually 185F).

Stage 2: operates when AC is on when the compressor is engaged.

Stage 3: operates when radiator reaches a certain high temperature (usually 203F).

I have seen some AC systems where Stage 1 is on when the AC is on and Stage 2 only comes on when a high pressure condition exists in the AC system.

My 91 Westy has the Small Car front AC system, but mine is set up to run Stage 2 any time the compressor is running.

My "override" switch is presently set up to kill the Stage 2 fan when it's not really needed while running the AC (below 85F ambient, or driving at highway speeds when ram air has the same effect).

I was driving in 95 degree heat today, listening to the Stage 2 fan cycle on and off (as it should) and wondering if the Stage 1 fan wouldn't be almost as effective as the Stage 2 fan for normal driving. There was a really great bassoon soloist on the radio and that Stage 2 fan was getting in the way of my enjoyment of the music.

I just replaced my radiator fan and don't want to do that again for a while, so that was motivating my thoughts. I live in Texas and my whole van setup is geared for fast highway driving in the summer.

I started to think of the ideal switch setup for what I wanted: an Auto, On, and Off option for both Stage 1 and Stage 2. That way I could defeat the Stage 2 (somewhat noisy) auto fan feature and force Stage 1 on, or force Stage 2 on when things are hot and heavy (uphill, loaded, in summer). I'm fine with leaving control of Stage 3 in the hands of the original VW feedback system.

As it stands, I notice that my overall coolant temperature, and subsequently my cylinder head temperature, stay lower when the AC is on and the Stage 2 fan is cycling. It's the simplest solution right now, and works well, but... I think I want more control.

I thought this switch idea might be relevant to your post. I'll let you know if I act on it.

kourt

[Syncro Jael]

[fxr]

You don't need a high current switch for my solution above ^^^.
And I was wrong - you only need an SPDT switch - a 2A capacity one will do fine:

edit - see my later post
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[Wildthings]

[Farf]

Do as "Wildthings" suggests. It might be easier to install a SPST (single pole, single throw) switch across the relay shown in the drawing. This keeps your system stock, your compressor will still shut off at 102C. The only thing that will happen when you flip the switch is your fan will run on high speed until you shut it off.

[Terry Kay]

<<Everything is great until the thermo switch see's that radiator temp is now at 102°c or 215°f and turns on the high speed fan and also cuts off the A/C compressor. Within minutes the cooling system begins to recover, turns the high speed fan off, and A/C compressor back on. But the interior of the van has now heated up due to the lack of A/C. So now it needs to work harder to cool the interior back off again. I also have this happen when off-road on slow trails keeping the windows closed so dirt and dust does not enter the van.>>

This is called a trade off in a low powered vehicle.
Long grades , high ambient temps, slow goat paths will stiefel efficient AC operation.
No if's and's or but's about it.

You want AC on the flats?
No problem.
You want AC on a slow grade?
No problem.
But on a long. steep grade, overloaded van, trying to keep her rolling, the little engine that could is going to need either all it has to get over the top,and your going to be sweating for 15-20 minutes, and then all will be good.

I don't know if it's a good idea to be shutting fans down when the cooling system is going to be requiring all it's got, and to be overriding the condenser fan to allow big operating pressures to build while that fan is off.

Kinda iffy to me--and if the AC is working as well as you have mentioned a couple of times, it'll get back down to a comfortable interior temps in no time.
You might be smoking the compressor with no fan running & much higher head pressures.

You may be overheating the engine on that long pull upward--

Sure something to be thinking about.

You can watch the engine temps on the gauge--how does one know how much pressure the compressor is overloading itself with with the fan off??

There's a good question--
I don't think you will know that.

Just food for thought---
_________________
T.K.

[Wildthings]

[Syncro Jael]

[MarkWard]

Looking at the wiring diagram you posted from the manual. You could unplug the AC compressor clutch relay and place a jumper wire between terminal 30 and terminal 87. This would effectively bypass the high temp cutout entirely with no manual intervention or wiring.

You stated that the circumstances were unique when the AC quit working. I imagine more often you are not in the high speed of the radiator fan and so the AC compressor clutch relay operates rarely.

If you find yourself in a unique situation again and you want to shut the AC off and on, you can use the AC switch to accomplish that.

I made up my AC wiring using the Bentley as a reference, but did not wire in the rad fan high temp cutout. It has not been an issue. I have rad fan low speed on when the compressor is on and the high pressure switch enables medium on the radiator fan when the high side pressure activates the relay.
_________________
☮️

[Syncro Jael]