AC Fan Switch Or Blower Bad?

[CrossT]

I have a situation where, on lowest AC fan speed, the fan does not come on most of the time. I am pretty sure the compresor is activated though. If I turn the switch to medium or high it works fine. Is this likely the switch or the blower? If the switch, is it cleanable or just R&R?

thx
todd
89 targa

[Steve 82SC]

If it's not working on a particular speed, the likely culprit may be the resistor pack. It's located directly behind the passenger side wooden floorboard. It's a very simple plug-and-play replacement. You shouldn't have a problem locating one as many people who've removed their air condtioning systems have these resistor packs sitting in a box never to be used again.

Steve

[CrossT]

I had not thought of that. Actually, I thought that item was just a temp sensor hooked to the thermostat for turning on/off the compressor.

thx

todd
89 targa

[CrossT]

The situation with my AC fan has changed and I wanted to revisit this before I buy something expensive. I posted this also on Rennlist but got nothing back WRT response.

Recently, I've noticed that, when on medium, my fan speed sometimes will waver downward and then back up to normal.

Also, I can confirm that on low speed setting sometimes there is no fan at all as I mentioned above in this thread.

On high, it seems to be consistent.

I am assuming as has been suggested here that my resistor pack is bad and that the problem isn't the blower motor.

If the resistor pack is the culprit, then an option seems to be the Griffiths/Keuhl variable speed control, which includes a new module replacing the stock three speed resistor pack. And would also solve the odd speeds of the orig three speeds.

From what I can tell the orig resistor pack is NLA ? ? The Keuhl piece looks nice, but is $300, so I wanted to post here again, before going for that.

Agree, disagree, other possibilities?

thx
todd
89 targa

[Steve 82SC]

Todd,







The AC in my '82 works just fine, but it is what it is.........it will never provide the extremely efficient cooling that a more up-to-date system provides. That being said, it's your dough and if you want to pop three bills for a rheostat type fan control, then go ahead. I don't think the resistor packs are available new any longer, but as I said earllier, there are plenty of guys that have deleted the resistor pack for a track car application. When I put out a request for one, a number of guys got back to me. Fix the problem for about $25 bucks and then see if you want to invest in improvements.

Steve

[CatSkynr]

The easiest way is to put a volt meter on your fan connection. When it works, what is the voltage. When it doesn’t what do you read. With a stuck motor, you will see a dip in voltage (inherent current draw), but there will be V there.

My blower motor was junk when I bought my car. It only worked on high, and then every once in a while it would squeal. I removed the motor and replaced the shaft bushings (lots of slack was found). I found with the use of a file and some Autozone generic plastic bushings, I made a perfect snug match. Then I soaked the motor in Tri-Lube with Teflon and let it drip dry over night. Wiped it down and ran the motor outboard with a rag close at hand to fling the remaining lube, reinstalled and since then for the last 5 or so years never had an issue.

As for cleaning your switch, yes you can as long as the reed points aren’t shot. Usually they are fine with a cleaning and they sound fine being the low setting ‘does’ work sometimes. Best is electrical contact cleaner (Trichloroethane). You can usually find this at ACE Hardware or your local elelctro-nerd-hobby shops. Just pull the switch and spray inward into the shaft. Then run the switch through its contact points to break up any debris. Do this a couple times. You can use alcohol, but it is not near as effective in removing debris and oxidation.

[CrossT]

Yep, you're right, try the cheap way first. Posting WTB on used parts board . . .

thx
todd
89 targa

[aj88cab]

Todd

I would consider CatSkynr's comments about the motor first, your comment about the medium speed fluctuation would indicate a binding motor. However when on the med setting, does it start at med speed and drop (motor issue), or does it start at med speed and rise to high. A rise from med to high speed may be a "normal" condition, possibly indicating a bad low speed switch contact.

Other than the motor, it could be a bad/loose wire or connector, a bad/dirty speed switch, or bad resistor pack. I'd still lean to the motor (based on your medium speed comment), but you can check the following before you spend any $$$.

>>The wire to check is the red/green wire at the speed switch, check the connectors and continuity to the resistor pack with a meter.

>>These tests are done with ignition switch in "run" postion. To check for a bad low speed switch contact put the switch at the low speed position. Then check the voltage at input terminal (red wire). Since the motor runs at high & med speed it should be 12v. Then check the low speed switch output terminal (red/green wire), if no voltage, it is a bad switch. If it showns 12V but the motor doesn't run, jumper between the red and red/green wires at the terminals. If the fan runs at low speed it is a bad switch. Clean the switch per CatSkynr's directions or replace. If the motor doesn't run it is a bad motor or resistor pack.

>>The resistors are nothing more than a coiled wire like a big light bulb filament. Check the resistors to make sure they are not broken or dis-colored. With all wires disconnected use an Ohm meter to check resistance, I don't have a value to check for, but both resistors should be close to the same resistance.

The resistor pack is actually a combination resistor pack and thermo bi-metallic switch. It serves two purposes as far as I can tell.

One purpose is the manual speed control. There are two resistors, at low speed the circuit runs thru both resistors, at medium speed the circuit runs thru one resistor, at high speed the circuit goes directly to the motor and doesn't go thru the resistors.

The second purpose I am not entirely clear on. It could be an automatic speed/temperature control, or thermal over-temperature protection for the resistors, or a combination of both. There is a thermo bi-metallic bypass switch located next to each resistor. If the temperature of the resistor is too high, the bi-metallic switch will close, bypass the resistor, and run the fan at the next higher speed (low>med, med>hi). When the resistor cools, the fan returns to the lower speed.

It would have been easy enough to use the same type resistor pack as the fresh-air blower to provide three fan speeds without the bypass feature. So the added bi-metallic switch seems to indicate a deliberate purpose such as an automatic speed/air-temperature control feature. But I'm just thinking out loud here.

I think that even confused me and I wrote it.
Good luck,
Andrew

[198491132]

Todd and All,

I have an 84 and am trying to replace the speed switch....the older switch and newer switch termination markings do not match. I have the wiring diagram, but it only shows the orginal part ID's. Question: new speed switch shows +, l,ll,lll,lV .....old one shows C,B,H,M,L

part number is 911.613.243.00.....

have you seen this replacement part and how do I transcode the markings?

Dave

[CrossT]

Guys

Thanks for the great suggestions on the AC.


Dave

I've basically given up on my 89's AC. I was going to dig into the intermittent fan issue when it stopped blowing cold air. I think I have a compressor seal bad given the line of oil on the underside of the deck lid. So, I have relegated the 911 to a non-summer car with maybe a few evening drives during the summer.

I'm sure someone here knows the answer to your question.

todd
89 targa

[198491132]

I spent some time with the ohm meter and old switch and I believe I have the wiring correct at this point. Looks to me like the blower....It has stopped working in the fresh air mode as well over the weekend. I seem to have voltage after the relay/fuse in the luggage compartment.. any other suggestions would be welcome, as the blower is the last thing i want to shell out money for...

Thanks, Dave