TheSamba.com :: View topic - Air Conditioning wiring issues and improvements. 89-91

Tue Jul 27, 2021 12:22 pm

I was aware from looking at the wiring diagrams to refrain from running my AC on #3 blower speed as it utilizes the AC relay (#3 pictured below)The AC relay is already tasked with providing power to the compressor clutch. I have redone the entire AC unit and it works very well. Even with ambient temperatures in the 90°'s fan speed 2 is sufficient for me, I am seeing a 40° differential. I generally run with the blowers on 2 and occasionally I will run on High speed position 4 for brief periods.
Picture (from kamzcab86) for reference.

The following references late model 89-91 Tintops which contain the AC wiring in the Left rear panel
I wanted to consolodate some good advice gleaned by comments on Dave's AC thread and also from a thread on the Vanagon Technical Depository Facebook group concerning a post where the OP's AC wiring system had caught fire. Dave's thread where he also posted that the AC relay had caught fire: https://www.thesamba.com/vw/forum/viewtopic.php?t=...p;start=0. I did not post these observations on Dave's thread because it encompasses his efforts to rebuild his AC system and is running into 11 pages.
The recommendations from others were as follows:
1.) replace the right side wire lug to the fuse as it is barely adequate for the current it must handle. The wire is listed in the Bently as a (6.0) European wire sizing that falls just above a # 10AWG disignation, the eyelet is 1/4" and it is the crappy open lug design that VW used . I prefer a closed lug design with silicone heat shrink to prevent corrosion or oxidization intrusion into the wire. If you plan on adding the thermal breaker below I would suggest just ordering some #10 with 5/16" eyelets. These are listed as SC6-8 in metric.

2.) Replace Blower high speed relay #2 depicted in the above picture to a 70 amp relay. Originally the relay was a 40 amp and it was superceded with a 50 amp. The 70 amp relays are easy to find, (same as what is used for the Radiator fan high speed circuit) and given the measurements I took, a reasonable action. The greater the contact cross-section and terminal thickness, the better. The relays can be found on eBay under a variety of numbers and manufacturers. Avoid chinese sellers. The so called 70 amp relays they have pictured are 40 amps when you recieve them. I ordered a German Fosser Brand that has 70 amp rating printed on the case. Currently there are some German Meistersatz 7M0-951-253 A / 4H0 951 253 rated at 70 amps From a US seller for around $12.00

3.) Add a 50 amp thermal breaker to the circuit. These can be obtained on eBay for $10 they will require 2) 5/16" #10 eyelets to interface. I recommentd they be placed in series with the existing fuse providing double redundancy and perhaps tripping before the fuse opens.

I did some preliminary measurements today which may indicate why some changes are neccesary. Running the AC in blower position 4 (high speed) indicated a constant draw of 45.7 amps on the system. I need to mention that my Van is a converted 1.8T and the clutch current may vary, but I doubt by much.
On Fan speed position 1 Current was 17.1 amps
Position 2 was 17.5 amps
Position 3 was 34 amps
Position 4 was 45.7 amps
Running the system just briefly on high speed with an ambient temperature of 84° produced a temperature of 132° on the supply wire insulation, the lug was around 140° and the fuse was at 145° Too hot to comfortably touch. In Dave's thread there was some question about the wiring as it splits to the 2 squirrel cage blower fans. I have a 91, the main power wire from the alternator to the fuse is 6.0mm2 diameter 10awg and is rated for 55 amps, the other side of the fuse to the highspeed blower relay is 4.0mm2 or #12 guage rated for 41 amps the wire exiting the high speed blower relay is a #12 guage going to a white connector which splits on the other side of the connector to 2 individual 2.5mm2 #14 guage wires (rated at 32 amps) going to each of the blowers. That connnector was at 130° when running the fans on high speed. Having seen 3 threads just recently outling that the AC wiring had burst into flames is enough to look hard at this area and I believe should cause some pause in anyone considering Redtek refridgerant due to the proximity of the lines to this area. At the very least relocating the pressure switch and ports if using redtek to eliminate leak potential in that area might be wise. I gaurantee that full speed blower relay is creating a good arc when the contacts close and it is not hermetically sealed. The AC relay probably does the same when engaging the clutch.

Tue Jul 27, 2021 1:54 pm

Since you have come this far and have the tools, why not measure the currents at the fuses for each of the 2 fan motors individually?
That will tell you what the true load is on the 3rd speed relay contact and the 4th speed relay.

Going by the numbers you already posted those currents appear within the max rating of the 2 relays.

Since you show speeds 1 and 2 load the rear power feed by 17 amps and speed 3 increases that load to 34 amps, that implies that the pair of motors is only drawing 17 amps through the a/c relay speed 3 contact.
Then you show speed 4 increasing to 46 amps which implies a 29 amp load on the speed 4 relay.

I'd be curious what the voltage changes at the fan motors are after some wiring rework so I'd first measure and record those values for each of the 4 fan speeds before making any wiring changes.

Measuring the current at each of the 2 fan fuses might also give you an idea of whether the fans are in similar states or if one has a problem developing.

Mark

Tue Jul 27, 2021 2:13 pm

I will record the individual fan currents when I go back into the system to install the breaker. I assumed them to be under 20 amps as they are individually fused on the ground line. Being within Max limits may be acceptable for a new system, but as evident by the fires recently an older system with contacts that are not prestine due to 30 years of use may not fare well. Fan motors that are sticky due to dust, cigarette smoke, or dry bearings will only add to the current demand. When I had my system down I took the opportunity to clean them, lubricate the bearings and tested the fans individually.

Tue Jul 27, 2021 5:30 pm

Excellent post!

Just linking to another fire thread.

https://www.thesamba.com/vw/forum/viewtopic.php?p=9684836#9684836

Tue Jul 27, 2021 5:38 pm

The AC relay is also powering the radiator fan up front on speed 1 while energising the compressor clutch. When put in blower speed 3 it is also running the evaporator blowers. Quite a load for it to dissapate. Most AC clutches are around 2 to 5 ohms, Indicating a maximum draw of around 6 amps. The major consumer outside of the blowers is the rad fan. My Rad fan is practically new. As is my AC clutch , so is my AC relay. I had to replace it some time back, the reading I am taking are probably an optimum scenario. Others need to do some readings on their systems with some age and /or a lack of maintenance. One solution I am contemplating is to seperately fuse the AC relay power to reduce the heat on the main fuse block.

Tue Jul 27, 2021 5:44 pm

Here is the AC fire thread I referred to on Facebook. https://www.facebook.com/groups/vanagontech/posts/1789051821271720

Look at the main power feed on the right of the fuse, It got toasty and the fuse did not open. A thermal breaker may be cheap insurance. The AC clutch relay may have been the cause for this one, I doubt it's rated for a slow blow 50 amp source!

Tue Jul 27, 2021 5:50 pm

Yeah, I snagged that photo too, trying to see where it started.
It seems to be the fan clutch relay area.
Mine clearly started at the high speed fan relay.

I have new relays to rewire each fan speed removing them from their current multi relay design.
I also have connection blocks to eliminate the over taxed 1-2 connectors.

I also plan on running a new heavier wire from the Alternator.

Dave

Tue Jul 27, 2021 6:11 pm

Looking forward to what you come up with. In the above fire the OP said that it melted through one of his AC hoses and he believes that the escaping freon estinguished the fire. Those running Redtek may experience a different outcome.

Tue Jul 27, 2021 6:25 pm

The rear A/C wiring only powers speed 1 of the radiator fan.
The radiator fan speed 2 is powered by a relay in the dash main relay panel position 5.
Once there has been a sufficient increase in the freon pressure a switch closes and triggers the radiator fan speed 2 relay up front.

I can see how adding a relay or 2 in the rear to break up some of the load might help things a bit. I'd want a second power feed wire from the alternator to completely separate some loads.

Mark

Tue Jul 27, 2021 6:48 pm

This is all a really great thread developing. As time goes by, I hope the various Bentley circuit path diagrams could be edited to show what improvements might de done and how they could be wired. It appears that a great deal of the 30 year old connections, wires, fuses and relays should not only be replaced and upgraded, but re engineered as well. The Redtek possibility of something going wrong in this area would be catastrophic. Until I can do all of this electrical properly with this level of input, being a bit too warm on a hot summer day seems a whole lot better that the van itself getting hot enough to call the fire department. Liquid or gaseous propane being showered over a burning relay doesn't sound like a fun way to end a trip.

Keep these ideas going.

Duncan

Tue Jul 27, 2021 6:50 pm

Note the resistors. 95°C Thermo switch on Rad enables low speed on Rad fan. It is also activated by the AC relay. Circuit e from AC rear wiring system activates the rad fan by energising relay # 5 less series resistance for speed 2 so you are correct, Power for the medium speed is supplied up front through fuse #1 . Both speeds 1 and two are activated by the AC system. Finally Speed 3 is enabled by 102°C contact of rad thermo switch which also deactivates the compressor clutch relay. The fast (speed 3) is powered by a seperate 50 amp fuse block and 70 amp relay located above the fusebox.

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Mod Edit:
Here are the rest of the 1989 and up wiring diagrams ........

The A/c wiring diagrams are titled "From 1989" so I can only assume that 89, 90 & 91 share the same wiring.

Tue Jul 27, 2021 7:59 pm

This thread is a bullseye to what's been occupying my mind after seeing a similar thread a few weeks ago, having been in the a/c electrical area and feeling how hot the wiring was getting and doing a few hot trips across WA state to Idaho in July and Aug.

I started today by running the a/c and taking a few temps. I frankly don't know at what temp things burn but these photos set a baseline.

The a/c cabinet as it stands today. This is a '90 Westy with 310K miles but the PO owned it for 20 years and may not have used the a/c at all ("just needs a charge" :D )

After running the a/c on blower speed four for 10 - 15 minutes...

I saw this wire get to about 200*...

This is about as hot as this relay got...

This wire at about 200*...

This was consistently the hottest relay...

I then allowed things to cool and ran the blower fan at speed two and temps dropped significantly to where I could handle all of the wires and relays. Since I never use fan speed four I may do the opposite of what Dave did and disable it at the switch (I believe I read that Dave disabled fan speed one).

I'll be wiring in a new fuse, possibly replacing the fuse holders for the 20 amp blower fuses, adding a heavy gauge wire from the alt to the bus and following the lead of the rest of y'all.

I intended to measure current for the blower motors but my weenie multi-meter maxes out at 10 amps. Time to get an amp clamp.

Great thread and great info posted elsewhere. Suggestions welcomed.

Tue Jul 27, 2021 8:00 pm

That A/C page from the Bentley diagrams has a few minor issues but I think it shows the point to point wiring well enough.

The radiator thermo switch settings are shown wrong for the years in question.
VW now calls for a 87 degree low speed and 93 degree high speed as the latest part.

A few of the wire colors are wrong as well, for the rad fan and fan resistor.

Mark

Tue Jul 27, 2021 8:19 pm

Original relays & fuse:

Upgraded relays with those listed in the image above, along with a maxi fuse and new high/low switch:

I'd take temp readings to compare, but I cut the A/C belt out last year. The hoses, condenser, and all that stuff needs replacing (system leaks, needs recharging every year) & I'm not doing any of that any time soon.🤷🏻‍♀️

Tue Jul 27, 2021 10:08 pm

Thanks for this great work!
Ever since I did the plenum delete I've never used the highest blower speed (or speed 3).
Great idea to disconnect fan speed #4.

With a blue-tape tag on the connector reminding me why it's disconnected.
And perhaps another note back in the A/C closet that speed #4 has been disconnected.

Tue Jul 27, 2021 10:16 pm

^^^Exactly, since the plenum delete speed #4 is an unnecessary racket. As for noting why it was deleted, I never thought of making myself a note that it was me(!), not the PO who did such a thing. I'll start backtracking all of my crazy changes that I'd eventually blame on the PO.

Wed Jul 28, 2021 12:13 am

Auto wire is rated at 80, 105, or 125c depending on type

You are running some hot wires there, and if it’s 80C rated wire at least one is in trouble.

Wed Jul 28, 2021 12:21 am

Just a note, I added all of the "From 1989" A/C wiring diagrams, it helps the reader to follow the current flow better.

I am beginning to understand the cooling fan relationship to the A/C being on.
If you follow wire "f" on current path 29 on page 97.145 it jumps the page to current track 28 on page 97.144.

Page 97.144 shows the A/C Compressor Clutch Relay as being normally closed ALL of the time........ A/C on or A/C off. The relay at rest completes the circuit.

The Compressor Clutch Relay does NOT cycle the clutch On/Off as you would expect it to.
The Compressor Clutch Relay does not activate/deactivate the compressor clutch as many other vehicles do.
The on / off clutch cycling control is handled by the A/C Relay seen on current paths 17-21 on page 97.144.

Anyway, the Compressor Clutch relay is normally closed when not powered. The Compressor Clutch Relay stays closed UNLESS there is an extreme overheat condition taking place. it is then activated and opens stopping the Compressor.
The Compressor Clutch is deactivated by the Radiator fan thermo switch 102° section closing, this thermo switch closing activates the Radiator Fan high speed THREE...... aka "Turbo Speed"!
This connection is clearly seen on Current path 31 at the relay terminal 4/85 on page 97.145.

Once the 102° Thermo Switch is activated it energizes the Compressor Relay coil breaking the electrical feed to the A/C Clutch.

Bottom Line?
The Compressor Clutch Relay is basically an Engine Cooling System safety device in this design,

Dave

greebly wrote: Note the resistors. 95°C Thermo switch on Rad enables low speed on Rad fan. It is also activated by the AC relay. Circuit e from AC rear wiring system activates the rad fan by energising relay # 5 less series resistance for speed 2 so you are correct, Power for the medium speed is supplied up front through fuse #1 . Both speeds 1 and two are activated by the AC system. Finally Speed 3 is enabled by 102°C contact of rad thermo switch which also deactivates the compressor clutch relay. The fast (speed 3) is powered by a seperate 50 amp fuse block and 70 amp relay located above the fusebox.
<snip>

Wed Jul 28, 2021 12:49 am

Just a note.......

These captures of the "From 1989" A/C wiring diagrams are rather poor and fuzzy.
If someone with a newer Bentley can provide crisper images I will edit them in and discard these fuzzy ones.

Dave

Wed Jul 28, 2021 6:01 am

kamzcab86 wrote:

Upgraded relays with those listed in the image above, along with a maxi fuse and new high/low switch:

Looks like the replacement fuse has suffered from some heat, the bottom looks slightly warped.