a/c condenser fan operation 1987 Westy

[dobryan]

I searched but could not find the answer to my question.

Can those who understand the 1987 a/c system and the operation of the condenser/radiator fan speed let me know how the system operates?

My specific question. The radiator fan comes on at medium speed when the a/c is turned on. I believe this is normal. Under what a/c circumstance should the fan switch to high speed (normal coolant temps though)? If the 'snowflake' a/c control is at max should the compressor cycle on/off at all or always be on?

Thanks!
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

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[Farf]

From the Bentley manual. Low speed fan should come on when a/c is turned on. Medium fan will engage when system pressure hits 15 bar. High speed fan will engage when coolant temperature hits 102 C and will also disengage the compressor. As far as the maximum cooling position, I suspect the system would cycle if you could get the internal temp low enough.

[dart330]

I can share my experience with using A/C on an 85, 87, & 90.

Low speed kicks on when A/C is turned on, medium speed only comes on when coolant temps get high. For me that is coming off the highway into stop and go traffic in the summertime.

High speed never kicks on due to just the A/C, and running the fan at low actually keeps my coolant temps from swinging above the led most of the time.

If I turn the snowflake to max, then the A/C does not cycle, just runs continuously. My understanding of the wiring is this tells it to ignore the temperature probe inside the evaporator. I typically don't run it in this mode for long periods of time, figure it is good to let the system cycle a little bit on long trips. Don't want to ice up the evaporator.

[dobryan]

[Farf]

Dave, the Bentley just shows a low pressure switch (2 bar) for compressor protection, if this switch exists on your van it would be easy enough to install a binary switch for both high and low pressure protection. If you are really motivated you could install a trinary switch (4 wire) and combine the 2 pressure switches shown on the diagram. Not sure if there are actually 2 switches in your system or just a single switch.

[dobryan]

Not trying to change the stock switch system just want to understand how it works.

So it sounds like my system may by reaching a high pressure of above 15bar more often than normal. The medium fan speed runs almost all the time.
_________________
Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646

Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794

[dart330]

Check out this post from GoWesty
https://www.gowesty.com/tech-article-details.php?id=74

I guess I can’t hear the low speed fan, and I have hit the high speed at least once where it turned off the AC compressor. When that high speed comes on, you really know it.

[dobryan]

That is an interesting post.

I'll ask a basic question since I seem to be confusing myself. What is the function of the a/c high pressure switch? What happens at 15bar or above?
_________________
Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646

Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794

[MarkWard]

From memory and I'm on my phone. The system is wired so that if the radiator fan temp switch activates high speed, the AC compressor cuts off. This would lower the condenser temp and get cooler air moving across the radiator. This condition should be rare. Rad Fan high speed is really a backup system to the medium speed system.


And to what was stated. Rad fan low speed should activate when the AC is on. When AC high pressure gets to a point, fan jumps to medium speed. If the low speed feature is inop, I would expect the Ac pressure to get high enough quickly, that medium speed would click in quickly. Going down the highway with optimal conditions, it’s conceivable that the rad fan would be on low. This is a basic description from memory.

In addition to the AC system, parallel is the rad fan temp switch. If coolant temp rises to a point, fan comes on medium. If the coolant temp continues to rise, rad fan switch turns on high and as I mentioned above AC compressor cuts off.

So climbing Pikes Peak with the AC on, probably past halfway coolant temp would turn the rad fan on high and AC would stop cooling.

I mimicked much of the factory wiring design, but opted to not have the AC high temp cutout.
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[Howesight]

Hi Dave:

I am guessing that it is hot in your part of the world. This, alone, might explain why your AC system is switching to the medium rad fan switch immediately upon switching your AC system on. Here in temperate Vancouver, we still get heat waves every once in a while. I wired my DIY front AC system to mimic the Vanagon 1986-1991 system in terms of wiring, so I can make a couple comments. On initial start-up in super hot weather, my AC system goes immediately to the medium fan speed. (So do all the Audis in our stable.)

1. The purpose of the "A/C Refrig. High Press. SW" in the wiring diaqram that Farf attached is to: Sense when a threshold refrigerant pressure has been reached and then to power on the relay that controls the medium speed on the rad fan. When the threshold refrigerant pressure has been reached, this is a proxy for the fact that there is insufficient air flow over the condenser to remove the heat being put into the refrigerant at your very hot (comparatively) evaporator. High ambient temperatures also mean that, even if you did not turn on your AC, the refrigerant in your engine compartment (in the compressor and hoses), in the long hoses, in the hot condenser (hot due to proximity to the radiator) and in the evaporator, will likely have your refrigerant already at 110 to 120 psi without even operating the compressor. Once you engage the AC system, the pressure very quickly rises to the threshold and the second-speed rad fan speed kicks on.

2. There are two ways that your low rad fan speed can come on, but only one is visible in Farf's wiring diagram: One, is from the 95 degree(C) rad fan switch making contact at 95 degrees and over. The second way is that the AC relay (a duplex relay that controls both the compressor and the rad fan low speed) sends power to the square box marked "12" in Farf's wiring diagram. This powers the center of "Rad Cool Fan Resist", which is the centre of the radiator speed resistor. In the diagram, it looks like two resistors wired in series, but in such a way that power can flow through only the last of the two resistors or through both of the resistors. When flowing through both resistors, the result is the lowest rad fan speed. When flowing through only the last one of two resistors, the result is the medium rad fan speed.

3. The "Rad Cool Fan Relay 3rd Stage" relay operates to bypass the resistors entirely and provide a full 13.8 volts ( or whatever alternator max voltage you have) to the rad fan. This is the "jet engine loud" mode. It only operates when the 102C degree side of the "Rad Cool Fan Thermoswitch" closed due to coolant temperature at or over 102C degrees. But note that whenever that 102C switch closes, this powers on the relay called "A/C Compress Clutch Relay" which is a normally closed relay, thus preventing power from flowing to the AC compressor clutch. This reduces engine load and stops the AC system from pushing heat into the condenser which is located in front of the radiator, the point being to reduce heat input into the radiator.

4. The power to the AC compressor clutch can also be interrupted by any or all of the following:

- The "Ambient Air Temp SW", which goes open any time the ambient temps are at or below a threshold like winter temperatures. I forget the spec, but assume it is around 50F or below.

- The "A/C Refrig. Low Press. SW" which goes open below something like 15 psi refrigerant pressure. This is intended to protect your compressor from damage caused by too low a refrigerant pressure. It is necessary to have a full charge of refrigerant to circulate the lubricating oil through the system and back through the compressor. If not circulating, then it can accumulate in places other than the compressor thus preventing the compressor from getting its proper lubrication.

- There is also, in addition to the switches shown in Farf's wiring diagram, another refrigerant high pressure switch that is wired in series with the wire (see wire "a" at the far left in the wiring diagram) that interrupts power through wire "a" if the refrigerant pressure rises too high. Again, I estimate that this interrupter switch goes open at around 300 or 350 psi, which would, again, be to protect the compressor from overpressure due to a blockage in the system, commonly found at a clogged Thermal Expansion Valve (TXV) or a clog in the condenser or otherwise.

Note that the "A/C Refrig. High Press. SW" in Farf's diagram is really mis-named. It should be called the "A/C Refrig. Medium Press. SW" The real high pressure switch is the one referred to in the above paragraph.
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'86 Syncro Westy SVX

[crazyvwvanman]

This "ultra-high" pressure switch compressor shutdown is a function of the trinary pressure switch found in the latest years only. The diagram above is the 86/87/88 setup before the change to the trinary switch with it's extra safety feature. Look at the later diagram to see it.

Mark

[Howesight]

Hi Mark:

Thanks for clarifying the differences with the '86, '87 and '88 versions. I was going from memory about the high pressure interruption switch. When I made my DIY front AC system and was trying to devise the electrical circuit, I looked at a number of wiring diagrams for the Vanagon system including the later '89 to '91 years.
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'86 Syncro Westy SVX

[dobryan]

Thanks for the info.

I have to take a trip later next week and I'll use the a/c and keep more careful track of what fan comes on when.

I wonder if the medium fan speed is making me think it is the high speed. I guess I need to start jumping connections to try it out.
_________________
Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

MD>Canada>AK>WA>OR>CA>AZ>UT>WY>SD
https://www.thesamba.com/vw/forum/viewtopic.php?t=620646

Building a bus for travel in Europe (euroBus)
https://www.thesamba.com/vw/forum/viewtopic.php?t=695371

The Western Syncro build
https://www.thesamba.com/vw/forum/viewtopic.php?t=746794

[MarkWard]

It’s hard to mistake the radiator fan on high. With everything functioning properly it would be very rare for the fan to run on high.

If I’m running down the highway with the air on, if I catch a long light at the exit is when I will hear it step up. Climbing slowly will cause it too.
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