Yet another question for the brain trust.

[cstreit]

It IS a temperature thing though. ...but not temperature of the engine, temperature of the output!

So why not use a temperature switch on the output of the AC itself. It the AC is running and the output is above, say 55 degrees, then turn the fan on?

[GH85Carrera]

Originally Posted by cstreit

It IS a temperature thing though. ...but not temperature of the engine, temperature of the output!

So why not use a temperature switch on the output of the AC itself. It the AC is running and the output is above, say 55 degrees, then turn the fan on?

I thought about that. It is a good suggestion. But what about the times in spring and fall when the AC is mostly de-humidifying the air and not working very hard. The temp will get that high and the fan comes on. That will not hurt anything but it is not needed then for sure.

I am one of the folks that only rolls down my window to talk to someone like a toll booth attendant or something like that. I don't ever ride around with the window open even on a perfect day. I have too many allergies. I drove an un air conditioned 914 for over 20 years. I have had a lifetime of open air driving. BTDT. I an't gong back. Either my heater is on or the AC is on.

A pressure switch might work if I could calibrate it to the high pressures, but that is going to be a challenge to graft into the system. The brake pedal seems to be the best suggestion so far.

[mattdavis11]

Originally Posted by cstreit

It IS a temperature thing though. ...but not temperature of the engine, temperature of the output!

So why not use a temperature switch on the output of the AC itself. It the AC is running and the output is above, say 55 degrees, then turn the fan on?

Not a bad idea, but the condenser is closer and easier to adapt a thermal sensor into the system he already has in place.

It's all about the delta T from condenser input and output, not the evaporator or vent temps, although 40 degrees at 100 ambient is a bit high for my liking. Should be down in the 20's

[GH85Carrera]

The 40 degree temp is the air temp with the fan on MAX blow. If I lower the fan speed it gets Down to 32 degrees air temp from the center vents.

[mattdavis11]

Drop the pressures a tad so where it nearly ices up the evaporator. LOL.

Naw, it's cold enough.

Did you integrate a cabin air filter to rid yourself of outside pollens?

[red-beard]

Flow switch.

Air Flow Switch for DC/ AC Voltage Supplies (Type 3201.-/3204.-)

These are factory set to 3m/s or about 10 feet per second. You will need to duct some air or place it in an area sure to sense flow.

[mattdavis11]

Now he has to go with a 24v DC supply. I like where this is going.

[red-beard]

Amazon.com: Dc/dc Converter Regulator 12v Step up to 24v 3a 72w: Car Electronics

[red-beard]

Actually, if he is willing to DIY, he could build his own flow switch.

Use a piece hard metal dryer duct with a flapper at the end. Put a switch in the duct so that the flap activates it when there is no airflow. You will probably need to add a weight to the flap to get it to activate the switch. I would put a relay inline, since these types of switches are not really well suited for lots of current.

[mattdavis11]

Now we're jumping the shark! Bout time!

[GH85Carrera]

James I like it! I would have NEVER thought of that.

Now I gotta figure out how big that is and where to mount it. It will have to be hidden fairly well. I love the out of the box thinking. It would be something to talk about when I show my boring stock 350 engine. As Spock might say Fascinating.

I will look into that as well as the speed sensor idea.

I was thinking about the speed sensor idea. I know that I can hook my laptop up to the ALDL and monitor output from the fuel injection computer. It shows the speed, and throttle position and O2 sensor readings. It also know what gear the transmission is in and other values.

Nothing can be changed from the fixed program, but you can see what is going on. I really need a motor-head 18 year old programming geek to figure out how to integrate all the readings just to turn a fan on and off.

[GH85Carrera]

Originally Posted by red-beard

Flow switch.

Air Flow Switch for DC/ AC Voltage Supplies (Type 3201.-/3204.-)

These are factory set to 3m/s or about 10 feet per second. You will need to duct some air or place it in an area sure to sense flow.

I could not find a price for that flow meter. It is 100 bucks or 1000 bucks? That does make a difference. Where did you find the metal vent? I need one of those for the house. Or crazy dog decided the plastic driver vents are tasty and destroys one about every two months.

[mattdavis11]

Originally Posted by GH85Carrera

Usually the only time I open the system is after another compressor dies. I use my AC a lot. A compressor last about 90,000 miles. The orifice tube is always replaced. For less than a buck it is a no brainer. Most of the time there is some gunk on the old one. The accumulator is replaced only if the compressor is replaced.

I did find this filter that I may order and have on hand for the next system purge.

A/C IN LINE FILTER

Hopefully the current compressor will last another few years.

The suggestion I like the most is to tie the fan to the brake lights. Now I need to figure out how to tie the brake light switch into a relay that will signal the fan to come on if the compressor is running.

So if the AC compressor is running and the brakes are pressed the fan runs. If either the compressor is not on, or the brakes are not on the fan does not run. It won't turn on when the compressor is not engaged either.


Forget the inline filter.
This is my current setup (no pun intended)

5 prong relay. Compressor closes one portion, then the brakes close the loop, energizing the relay to turn the fan on.

[Nostril Cheese]

Just go off the TPS.

[GH85Carrera]

Originally Posted by Nostril Cheese

Just go off the TPS.

That is very logical. I just need to figure out how do do that.

[john70t]

Originally Posted by mattdavis11

Now we're jumping the shark! Bout time!

We're going to need a bigger ramp: variable pitch propeller | eBay

[mattdavis11]

Originally Posted by Nostril Cheese

Just go off the TPS.

Going to then have to figure out how to get more output to make that relay work. TPS range on a TBI motor is said to be .5v to 5v DC at WOT.

[beepbeep]

Hmm...my Audi has a visco clutch fan + electric fan that only kicks in when gas pressure is too high = cooling flow is bad. Can't you use something similar?

[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.

RB's idea sounds pretty good except for the same problem. Same with the GPS. The solution can't have anything to do with speed, motion or air flow, IMHO.

The orifice sounds interesting, but even with the explanation I don't completely understand if it will do what Glen needs to do, activate a fan in hot conditions when stopped. The in-duct temp sensor might be tardy in operating the fan and shutting it down. He could be doing 40 before the duct temps fell.

That's why he asked here because if it were easy, he'd have done it already.

I guess I'd install a horn button within reach and use the horn ring to run the fan. Not going to help the valet.

[Lapkritis]

I would not touch any reference voltages with the ecu. I like the brake light switch recommendation as it's 12v and not ecu/tune impacting at all. Just put the relay in series with the clutch feed so only when ac is running. Cost is near nil.

You could also use a shift light with programmable 12v output to kick a relay as well.