Yet another question for the brain trust.

[Nostril Cheese]

Originally Posted by Zeke

I don't think cheese meant to use the TPS voltage, just the movement to activate a switch. Problem with this is having the fan run on cool days and cold nights at idle.

Exactly, pop the cover off and put an extension on the shaft.

[GH85Carrera]

Ok, after looking around at possible solutions here is what I came up with.

Thanks Matt for the idea.

Get another fan relay just like the first one.



In this crude drawing I flipped the relay 180 degrees. Just power that new relay from the old relay using the wire that did run the fan.

The ground is the same but the sensor now it the 12 volts of the brake lights just like the old one saw the 12 volts from the compressor. The output of the second relay runs the fan.

Now the fan will only come on IF the compressor is running & the brakes are on.

The fan will come on anytime I hit the brakes if the compressor is running even if it is when approaching a corner. This is not the most elegant solution, but it will keep the fan from running while cruising down the road. It would be cool to figure out how to add a 5 to 10 second delay from the brakes coming on until the fan starts.

OK folks, will this work?

[red-beard]

Not in a parking lot.

[GH85Carrera]

Originally Posted by red-beard

Not in a parking lot.

OK, why not?

Unless you mean while the transmission is in park and my foot is not on the brakes.

[red-beard]

With the parking brake on, your foot will not be on the brake. The fan will not operate.

[red-beard]

Glen, I don't think your design is bad, but I think if I were doing this, I'd add a manual switch in parallel. This way if you were stopped and parked for a while, you could switch the flip and get colder A/C. It would also work as a backup main cooling fan.

[GH85Carrera]

Well yea, I thought about the few very few times I am stuck at a train crossing. Now I just put it in park and park and sit. Now I will have to rest my foot on the brakes. No big deal.

[wdfifteen]

Make your own pressure switch. Mount a normally open push button switch behind the grille. Make a flap out of aluminum flashing and mount it on a light hinge (like a piece of duct tape)at the top so that it will press the switch when air pressure against the aluminum flap is great enough. Wire your aux fan through the switch. Adjust the speed that it activates the switch by trimming the aluminum to the right size.
This is such a simple, elegant solution that you should figure a way to mount it on top of the hood so everyone can see it.

[red-beard]

Simple, yes. Elegant? No.

[GH85Carrera]

Originally Posted by wdfifteen

Make your own pressure switch. Mount a normally open push button switch behind the grille. Make a flap out of aluminum flashing and mount it on a light hinge (like a piece of duct tape)at the top so that it will press the switch when air pressure against the aluminum flap is great enough. Wire your aux fan through the switch. Adjust the speed that it activates the switch by trimming the aluminum to the right size.
This is such a simple, elegant solution that you should figure a way to mount it on top of the hood so everyone can see it.

I like the theory, but I see problems. It is windy in Oklahoma I could be sitting at a light and the wind could keep the fan from running.

[1990C4S]

Buy a 12VDC on-delay relay. 5 to 10 second delay....

[onewhippedpuppy]

Originally Posted by Nostril Cheese

Just go off the TPS.

My thought. How does it sense and control idle? The EFI on my '88 Carrera had a microswitch that sensed when the throttle returned to idle position and activated the ICV. Very simple, just a microswitch that was pushed in by the throttle linkage. If yours has a similar switch, you could tap it. Otherwise you could just rig up a microswitch that was pushed by your throttle linkage when at idle.

Edit: here's the microswitch used on the Carrera, you can look at the diagrams to give an idea of what I'm trying to explain.

http://www.pelicanparts.com/cgi-bin/smart/more_info.cgi?pn=911-606-013-00-M100&catalog_description=&Microswitch%252C%2520%2520%2539%2531%2531%2520Carr era%2520%2528%2531%2539%2538%2534%252D%2538%2539%2 529%2520

[mattdavis11]

From what I gathered, Glen was looking for a simple solution utilizing what he has already. The way you diagrammed it is exactly the way I had in mind.

The peanut gallery here is pretty rough, but if you want to please them, refer to the other two methods.

As an a/c guy, I prefer the cooling fan pressure switch grafted into the condenser or liquid line previously mentioned. The Derale fan controller with a probe would be second.

The reason I like those two approaches better is because they are not dependent on driver input. They activate the fan automatically depending on pressure or temperature. As previously discussed, as the pressure rises, so does the temperature of the condenser.

[GH85Carrera]

No doubt the pressure of the condenser would be ideal. It will be a challenge to figure out what pressure point is ideal.

[Dueller]

Haven't read all responses but had an identical problem on my 528. Replaced fan clutch and it works perfect even at long traffic lights. YMMV

[mattdavis11]

We've passed up the option for a new fan clutch, a variable orifice tube and a parallel flow condenser. LOL

He has an electric fan, and wants to use it.

[RANDY P]

That compressor has a high side trigger that's supposed to CLOSE the vents to recirc when you are on MAX A/C- in other words, it supplies a ground when either you go to MAX, or high side pressure reaches a certain point- like the temps are high..

Without going complicated you can run a relay off of that, and trigger your fan. So when it's on MAX the fan activates. You can't run on MAX all day, it's not healthy (no outside air) so, at idle switch it over, let fan turn on.

Otherwise, you may need some seriously messed up electronics to make it seamless- like a VSS tapped to the cruise control sensor thing under hood.

OH- you can also go off a sensor on the upper hose, when it gets to a certain temp (215?)- fan triggers.....only way you'll hit that temp is idling.

rjp

[RANDY P]

Originally Posted by mattdavis11

From what I gathered, Glen was looking for a simple solution utilizing what he has already. The way you diagrammed it is exactly the way I had in mind.

The peanut gallery here is pretty rough, but if you want to please them, refer to the other two methods.

As an a/c guy, I prefer the cooling fan pressure switch grafted into the condenser or liquid line previously mentioned. The Derale fan controller with a probe would be second.

The reason I like those two approaches better is because they are not dependent on driver input. They activate the fan automatically depending on pressure or temperature. As previously discussed, as the pressure rises, so does the temperature of the condenser.

this.

[GH85Carrera]

Originally Posted by mattdavis11

From what I gathered, Glen was looking for a simple solution utilizing what he has already. The way you diagrammed it is exactly the way I had in mind.

The peanut gallery here is pretty rough, but if you want to please them, refer to the other two methods.

As an a/c guy, I prefer the cooling fan pressure switch grafted into the condenser or liquid line previously mentioned. The Derale fan controller with a probe would be second.

The reason I like those two approaches better is because they are not dependent on driver input. They activate the fan automatically depending on pressure or temperature. As previously discussed, as the pressure rises, so does the temperature of the condenser.

I really appreciate all the input. I really do. No doubt the pressure switch is the best way to go. BUT, that requires recovering the R-12 and opening some connections that are factory sealed from 1986. I have flushed the condenser several times over the years when I replaced a compressor. I have never removed the liquid line from the condenser to the orifice tube. I know that is not a big deal, just another place for a new leak.

I was hoping to do this the lazy man way and just add a relay. I have owned the Elky since October of 1991. It is my daily driver. I have personally driven it 280,000 miles. I know the car. The AC has operated the same way since 1991. It is not a major inconvenience, but it is annoying. My Elky operates better in every way than when factory new. With a 4 speed lockup transmission, limited slip rear end, a fuel injected 350 and numerous other improvements over the years. If my fairy god mother came along and said she could wave her magic wand and make it just like it rolled off the showroom floor I would punch her in the face and break her wand.



If I take off the liquid line and take it to a local AC shop I presume I can get them to splice in a T connection for a high pressure or temp switch. I would for sure would like to have a inline filter added. There is always some minor gunk on the orifice tube every time I replace it. I guess the T connection would have a Schrader valve so I can change the pressure switch without recovering the refrigerant.

[mattdavis11]

Glen, all the connections are sealed by o-rings. The factory didn't invent them and they are cheap.

Any a/c shop should be able to incorporate a tee into the liquid line to allow for a pressure switch. 7/16 or 3/8ths thread for a female pressure switch is your best bet for testing. Your accumulator has a schrader valve for the LPCO, it would be the same.

If you decide to go that route, I'd place the T on the liquid line just after the union from the condenser. If you choose to adapt an external thermo fan controller, anywhere near that union or in the condenser fins would suffice. Wrap it if you put it on the line.

I don't think you should be having this problem with an R12 system though. Having admitted that your vent temps are 40 degrees with an axillary fan tells me four things, 1) the compressor is weak (hope it's not a compressor works), 2) too much oil in the system, 3) bad fan clutch, 4) external fins on condenser won't allow air flow.

Your system should blow in the 20's all day long.

Another in line filter (orifice tube is one) just creates another possible restriction, but if you insist, I have one for an R4 that mates to the back of the compressor before the hose assembly.

Edit: five things, 5) overcharged.