PWM for Rear AC Blowers - Install

[Syncro Jael]

I installed a PWM (Pulse Width Modulator) to the rear AC Fan Blowers so that I can do away with the resistors and have variable speeds to the fan.

You have to run a dedicated ground wire from the rear pillar to the dash. I used a 12 gauge wire.

In this pic you can see the ground wires ground to a bolt on the pillar. Take the nut off, remove only the grounds coming from the blower fans. These will be the ones with the fuses attached. Make sure to keep the other grounds attached and replace the nut.

I then attached the ground wire that is going to the dash to the blower fan grounds. I used a small bolt to combine them and later heat shrink-ed a cover over this connection. If you look at the photo you can see it. I did this so it is easily reversable.

Here is the PWM that I installed:

Description:

This is a simple and easy-to-use DC motor speed controller of elegant appearance and stable performance. It is made with high quality circuit board which ensures a longer service life. The input voltage can be DC 10V to 50V and control power from 1200W to 5000W(peak). This speed controller is a universal one which can be used on many DC brush motors in car cooling fan motor, car air conditioning motor, exhaust blower, etc.


Features:

This simple and easy-to-use DC motor speed controller has an elegant appearance and stable performance.
This motor speed controller is of high quantity for industrial use that can work normally when operation temperature is below zero Celsius.
Well design case can protect the controller board from damage as well as dissipate heat. Universal speed controller can be used for DC brush motor, suitable for car cooling fan motor, car air conditioning motor, exhaust blower, treadmill motor, etc. This motor speed controller can also be used for dimming DC lamps or controlling DC heater.

Specifications:

Working Voltage: DC10V to DC50V

Max. Rated Current: 60A

Peak Current: 100A

Control Power: 0.01W to 5000W

Power Alters According to Voltage:

12V*100A =1200W
24V*100A =2400W
30V*100A =3000W

50V*100A =5000W(peak)

Quiescent Current: 0.04A( not over 40mA when voltage is DC10V to DC30V)
PWM Duty Cycle: 0%-100%
PWM Frequency: 15khz
Operation Temperature: -20 to 40℃

Size: 14.6 x 8 x 3.8cm / 5.74 x 3.15 x 1.49"

https://www.amazon.com/gp/product/B07L8HX8LB/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1

Remove the control knobs on the dash for the AC system. Then carefully pry the plastic square mount. The pins are on the top and bottom. Once you have the switches out, unplug the one that adjusts the blower fan speeds. Normally you have 1-2-3-4. You want to use a spade connection on the yellow wire. It is the high speed. I did this so it is easy to switch back if you ever have the need. The plug is not modified at all. Your wire will run from that yellow wire connection to the + terminal on the PWM out. Your ground that you ran from the rear blowers will go to the - terminal on the PWM out. Attach another wire with a single spade terminal and attach it to the positive or power on the same plug. You will notice that the blower gets it's power from the other plug that turns on the AC and adjusts the temperature setting. This will go to the Battery + terminal on the PWM. Then run a new ground from the dash, or use the terminal off the ground tree that is open. There is plenty of room for the PWM up under the dash.

Make sure you have the reversing switch paddle the correct way or you can just cut the wires and splice them direct.

You will have to fabricate a piece of plastic to cover the hole and drill a new hole for the new switch. Pretty simple really.

I painted the blue on the switch white to match the VW theme.

Now enjoy variable speeds and it uses a lot less power than going through resistors!
_________________
1987 Syncro Westfalia Hightop - NAHT
Subaru EJ25 Forged Frankenmotor, Triple Knob.
Jael = (Mountain Goat)

[MrTibbs]

Very nice.

Questions: Where did you mount the circuit box?...and did you do anything to the temp selection switch as well?

[jimf909]

Cool (hehe). You along with ItalJohn are making these PWMs look very attractive. The two big resistors in the AC cabinet look like trouble and constrict an imagined storage space available on each side of the blowers (with speakers removed).

Have you toyed with the idea of replacing the PWM control knob with the oem VW knob? That would make my sense of symmetry happy.

_________________
- Jim

[bobbyblack]

Holy cow! That is awesome! I was puzzling out how to extend the 5 control wires from rear to front.. You solved it very well with the single dedicated ground. My controller seems to be a similar unit to the one you installed. Did you choose the 50A unit for a specific reason? I scratched around a bit and thought I saw 30A mentioned for the rear blower(s). I saw that ItalJon's 30A unit was not in stock, but he was using his on the front blower. I got a 40A, I believe.

EDIT: its a 60A unit...

Question: Does you method still use the power relay in the D pillar to switch power on? In my case, that is the one or next to the one that got hot enough to melt internally. Scared me pretty bad, and stank the cabin up a lot. If I were to extend the 5 wires and locate the the PWM in the D pillar, could I avoid more of that wire harness back there? Or does your method avoid that entire relay area?
_________________
'87 Westy 'Flossie','86 Westy 'R1','86 tintop GL - Subi2.2 'J2','83.5 stock tintop L 'ZoomBus','74 Karmann Ghia, '63 Notch

[nocreditnodebt]

I don't have a VW, but have bypassed my resistor based Hvac blower speed control with a 40 amp continuous /60 amp surge PWM motor speed controller.

I've also wired it to be able to turn on with engine off/ no Key in ignition, and can unplug and swap 45 amp anderson powerpoles and return the original speed switch with resistor pack to control, though I see that, as increasingly unlikely to ever occur.

I would caution against using PWM motor speed controllers with less than a 21Khz frequency, as they can make the motors, or even LEDs whine annoyingly at reduced speeds/brightness levels, especially to younger ears.

The original E bay listing is no more and I can't find it elsewhere, but my 21khz unit looks like this one, without the additional pushbutton display/controller, and was just under 17$.

https://www.ebay.com/itm/DC-9-60V-40A-60A-Digital-...SwCZZdLW06

An electronics guru friend of mine ordered one first, and declared it to be 'built like a tank' so I got one too, and i am glad i Did. Mine has the on off switch combined with the potentiometer. The endcaps have a soft silicone gasket and the wires are also going through this silicone gasket. I'll guess it is at least IP67 rated, except for the potentiometer.

The transistors are using the casing itself as a heatsink, and the only lack of quality I can discern is a lack of sufficient thermal compound between the transistors and casing. Regardless, the casing barely gets warm passing 15 amps for a half hour( 14.7v battery voltage), and i think the unit is cruising along unstressed powering a still healthy blower motor at less than half its amperage rating.



Mine is not reversible, but cage fans do not really work well in reverse anyway.

I have ran a dedicated 8awg feed to my dash to power this PWM MSC and blower and with another 45 amp powepole outlet up there too. Huge difference in airflow with 14v reaching motor vs 11.5v. Amp draw is nearly double too though. I've never captured the data regarding how much juice the resistors waste at reduced speeds. I figured I'd need a way to measure motor rpm for any viable comparison, and I don't trust my tools to measure voltage properly after a PWM MSC does its thing.

Anyway in my opinion, the PWM MSC is awesome for infinite speed control of HVAC blower motors, being more efficient bypassing the resistors, and also allowing for higher voltage to potentially reach the blower motor, if wired thickly.

I can also easily remove it, and since I have powerpoles everywhere on most everything, use it inline on many other devices to slow motor speed or LED brightness. it works fine on brushless motors too.

[Syncro Jael]

[Syncro Jael]

[bobbyblack]

Turns out I got the same, or very similar PWM as in the first post of this topic. I had a hunch that there was more to be done, just a little shy on the single dedicated ground method above. I decided to wire the PWN into the existing plugs, same effect as original intent to easily go back to stock arrangement if desired. I found some of the heavier wires from one of my Subaru harness pulls, and arranged the power to the PWM battery + coming from the big black wire from the center relay which would normally go to the two big black wires going to the motor, and - to the fused grounds. The PWM terminals for motor + and - went to the other sides of those same connectors. Had intended to put the spades, etc into plug blocks, but didn't have the right combination of plastic housings on hand.

Tested it all in the rear, by switching on to 4 up front. Then I extended the on/off and variable POT/switch with a multi strand wire up to the dash. Works as hoped.

_________________
'87 Westy 'Flossie','86 Westy 'R1','86 tintop GL - Subi2.2 'J2','83.5 stock tintop L 'ZoomBus','74 Karmann Ghia, '63 Notch

[AllRad]

Hello,

I had the AC system recharged after a decade of no AC (from prior owner) on my 1991 Syncro Tin Top. All seems to work fine. Although I noticed that the red wires in the 'D' pillar get hot to the touch. Be that as it may, the more obvious problem is that the dual blower motors only work on the highest setting. I've been reading this post about installing a PWM. Before I go the PWM route, I wanted to confirm that it was failed resistors to the blower fan motors as the root cause. The shop that recharged the system, claims they tested the fan speed switch and the motors and both are fine (not sure I believe that...)

This seems like an obvious resistor issue, but there are two -- one for each blower motor. I own a multimeter, that I barely know how to use. With it set to 200 Ohms (Omega symbol), it shows that both resistors have nearly identical numbers after repeat readings.

--> Is it strange to think they are both dead, if they show identical readings?
--> I have no idea what the numbers actually mean. Choosing a different Ohm setting on the meter yields different, but consistent numbers between the two resistors.

A: 1.7 B: 0.7 C: 0.4

[/img]

Here are some bonus pictures for anyone taking on this chore:

[bobbyblack]

Coincidences happen. It sure could be that getting everything hooked back up, ran for a bit at the shop was melting the "hot to the touch" bits back there enough to cause your symptoms. However, since all you need is full closed circuit - no resistors - with the PWM (on #4)in between, try it. Funny how things go. After rewiring a whole new A/C harness into place, I didn't change the two 20A fuses. Guess what blew on the way home yesterday?
Just my observation, but my newer harness prior to PWM was, in my opinion, 1/3 less hot than what I felt on #4 before.
I took it slow, tried to be methodical. Now with the PWM, the oversized wires in my homebrew PWM harness are very much cooler to the touch on full.
_________________
'87 Westy 'Flossie','86 Westy 'R1','86 tintop GL - Subi2.2 'J2','83.5 stock tintop L 'ZoomBus','74 Karmann Ghia, '63 Notch

[bobbyblack]

AllRad,

Thought over your issue overnight, and looked again at your pictures. Thus, have to ask something: Where are your control switches and wire to them running now? That wire bundle with the on/off and temp dial usually go through the tube and you reach up over your head to turn them on 1-2-3-4 / cooler. Kind of important that those wires all reach from your new switch location all the way back to the D pillar.

Also, I've had a few of the original switches apart. For me, pulling the switch apart from the wire block behind it was HARD, and I broke one quite easily. Thus, what you may be looking for is if the shop took apart the switch to test ONLY the switch, and ONLY tested the blowers, perhaps there was a problem in the wires from the plug block up front to the harness connectors in the rear. That would be easily checked, all wires should be color coordinated from the plug block up front to the back. Just be sure that each has continuity before you dig too deep on those resistors. They are probably just fine, and not the issue at all.

-bobby
_________________
'87 Westy 'Flossie','86 Westy 'R1','86 tintop GL - Subi2.2 'J2','83.5 stock tintop L 'ZoomBus','74 Karmann Ghia, '63 Notch

[AllRad]

Hello Bobby,

The controls on my model are in the dashboard (to the right of the radio). I don't happen to have a radio installed; So, pulling out the ashtray and removing the map box provide decent access. I was thinking of swapping the actual switch, using the heater switch as a tester. I have yet to try that.

The wires do not go through the ceiling duct. They must run from the dashboard area to the back of the van on the underside?

It looks to me like the resistors are fine, the blowers are fine, something is amiss somewhere else. I can only think of it being the switch itself (inspite of what I was told), or the wire connections from the switch to the back of the van.

Is there another variable I could be missing?

It does run on high speed. Is it a clue that the red wires are hot to the touch? Like uncomfortably hot!

[bobbyblack]

Mine were HOT HOT before I found a newer harness and replaced it. Then, after I did so, and made sure all the speeds, etc. worked as original, I again did the 'touch-test' and the fat red ones were still fairly warm with the blowers on Hi. LOTS cooler though.

So, after the PWM install, I felt of the fat red's while the blower was on full blast, and the reds are a bit cooler.

Also, those yellow fuses back there are open-wire 20A fuses, could actually be original as I believe those same ones on mine were, which worked fine for a few days, but then didn't. I replaced those with modern 20A fuses, and the red wires are a bit cooler yet.

[ I am grumpy that my kids thought my IR temp gun was a toy and have not put it back in my tools, so I don't have real numbers here, sorry. ]

Anyway, I would replace those two old yellow fuses regardless of your other issues.

(hint)
In my case, I had two spare blowers, and took all 4 to load test. They were all the same so I put the newest ones in and closed up the cabinet. It is easy to rig up a couple of wires from a jump pack or whatever 12V power source, and test each blower.

I still think you could continuity test the blower wires from switch to the rear harness for speeds 1-2-3. Perhaps those are just not sending power..

However, as long as 4 works, you've got what you need for the PWM install. I felt the rear was the right place for mine. I have no understanding of how all those relays work in back, but I would fear that the power wire from front to back for #4 setting is not actually the one carrying the full draw of the motors, and instead, that a relay is getting hit with a function it may or may not be intended for.

{EDIT]

Take a close look at your grounds behind there.. More often than not, its the weak ground that makes other wires/fuses have troubles. I can't tell if those grounds have been disturbed lately, but the threaded stud looks rusty. Shine all that up good.

-bobby
_________________
'87 Westy 'Flossie','86 Westy 'R1','86 tintop GL - Subi2.2 'J2','83.5 stock tintop L 'ZoomBus','74 Karmann Ghia, '63 Notch

[AllRad]

I very much appreciate the advice. This forum is invaluable!

So, I swapped the ancient fuses, and I polished the ground terminals as best I could. Then I ran the AC with the motor on for about 10 minutes, and the red wires are most definitely not as HOT as they were before. Now, they are a comfortable warm temp. My worries about that are basically dismissed. Nice!

Nasty

Mo bettah!

Thanks for the tips Bobby!

[AllRad]

While fooling with it, I noticed (by accident) that when I switch the fan speed to #3, there is a consistent shlacka-clacking noise coming from the back of the Van. At first I thought maybe the blowers were spinning at a very slow speed. Of course, with the blowers on #4, nothing is audible.

When on fan speed #1 & #2 there is near total silence.

On speed setting #3 the blowers sit idle, but the temperature controller makes a stream of schleack-clacka-clack sounds.

Does this mean anything to anyone? Bad AC Thermostat, per chance?

[robertgriner]

Not an electrician, nor claim to be very knowledgeable, but are the specs on Ron’s original PWM the “preferred,” or “required,” for Amps/Voltage, etc?

I have found several others on Amazon, but not going up for a Max of 100A.

https://www.amazon.com/hz/wishlist/ls/2ARAD13UXN33H?ref_=wl_share

Also...some “how to for dummies” questions:

1 - Can you disconnect and remove the resistors in the Blower/Evaporator Cabinet

2 - Is the temp range removed from operation in Ron’s setup? It’s “all on,” or “all off?”
_________________
"Maxx" - 1988 Westy || Tiico Conversion
- 286K+ and going strong!!

[26kick]

[vanis13]

Would this PWM work on an early AC?

Might it solve my HOT fan wire issue? https://www.thesamba.com/vw/forum/viewtopic.php?t=782163&highlight=

- Some thoughts:

The early AC has a single/combo temp switch for both the fans and the temp

What might the wiring for the PWM be like? looks like the early has 3 resistors instead of 2 (AC schematic below)

For someone who doesn't know about PWM - Which one to get? What else would need to be ordered?

Thanks in advance for educating me on this

_________________
83.5 Westy with Subaru 2.5, 4 spd manual, center seat, COLD A/C on 134a!, Winter camp heated with an Espar B4 gasoline furnace

www.SuperVanagon.com - some stuff I make

[vanis13]

bump
_________________
83.5 Westy with Subaru 2.5, 4 spd manual, center seat, COLD A/C on 134a!, Winter camp heated with an Espar B4 gasoline furnace

www.SuperVanagon.com - some stuff I make

[breakpunk]

slight bump +

Once the PWM is in, can all the other now obsolete stuff get pulled out?? (mostly the wires that run between the old switch and the resistors). I've been poking into my diagram and it looks like the AC relay can even be split into two standard relays once all the Resistor wires are yoinked.

I worked up a diagram of how I interpreted the recommended routing w/dedicated ground & my 'deleting' exercise.