adding a condenser aux fan

[sixto]

For a car that doesn't have a refrigerant temp switch, how do I trigger an auxiliary fan? Temp sensor through the condenser fins?

Thanks,
Sixto
87 300D

[tjts1]

Have the conpressor clutch circuit trigger the fan.

[Mike D]

You can use the clutch circuit as suggested but wire it through a separate voltage relay. The draw back to activating it in this manner is you will also activate the fan when the defroster is on, depending on your system.

[sixto]

Won't that trigger the aux fan when I'm going 65 mph?

Sixto
87 300D

[Mike D]

Yup. Of course if your car had the condenser fan originally installed it would be on at 65 anyway.

What are you working on?

[leathermang]

Why is this in the Open Discussion ?

[Mike D]

I'm guessing it's because it is for a non-Benz vehicle and the other forums are for Benz related topics.

[leathermang]

How in the world would someone know from the first post information...that this was not about an MB? Anyway, lots of non MB ac questions get asked and answered where the AC guys hang out..

[tjts1]

Yeah! Lets get outraged by a technical question.

[sixto]

97 Suburban 6.5td. No aux fan, big honking clutch fan. Maybe the clutch fan should engage sooner but engine temps are in check per the gauge so I'd rather not mess with it.

I'll put a test light on the MB to see if the aux fan comes on when the car is moving. I doubt it since the aux fan doesn't blow all the time the compressor's engaged with the car idling. I expect air flow through the condenser at speeds above creeping in traffic keeps the high temp switch quiet.

I'm glad to catch LMG's attention How do I trigger the fan more selectively than when the compressor's engaged?

Sixto
87 300D

[leathermang]

Originally Posted by tjts1

Yeah! Lets get outraged by a technical question.

What is your problem ?
What I was pointing out... which is true.. is that an AC question will not get the ' traffic ' over here that it will on the Diesel Forum..

[leathermang]

Originally Posted by sixto

.....I'm glad to catch LMG's attention How do I trigger the fan more selectively than when the compressor's engaged? Sixto 87 300D

Some of those types of things are now more controlled by the auto manufacturers trying to get their average MPG's up to meet some ' goal ' set by the govt..than by logic... or they try to get too tricky to be reliable .... or settable... like they did with carb adjustments...
So it might be most reliable and controllable just hard wiring a switch to a relay to run it... In your moderate climate that would probably be a part time deal... ....

[Yak]

Originally Posted by sixto

97 Suburban 6.5td. No aux fan, big honking clutch fan. Maybe the clutch fan should engage sooner but engine temps are in check per the gauge so I'd rather not mess with it.

I'll put a test light on the MB to see if the aux fan comes on when the car is moving. I doubt it since the aux fan doesn't blow all the time the compressor's engaged with the car idling. I expect air flow through the condenser at speeds above creeping in traffic keeps the high temp switch quiet.

I'm glad to catch LMG's attention How do I trigger the fan more selectively than when the compressor's engaged?

Sixto
87 300D

For "more selectively" triggering the fan, it depends on how much you want to tinker. I'm not exactly sure of your intent. Do you want a secondary method of turning on an already existing fan (the clutch fan), or a way to control another fan that you'd add?

A basic $30 kit from a trailer supply: http://www.etrailer.com/p-D16735.html

An adjustable one: http://www.etrailer.com/Radiator-Fans/Derale/D16769.html It says from 32 to 240 degrees. Take note that the temp has to drop 10 degrees to turn off. This also keeps the fan from cycling on/off exactly at a single trigger temp.

Or something a little more complex: http://www.jegs.com/i/JEGS-Performance-Products/555/52126/10002/-1?parentProductId=1557724

You could build your own comparator circuit and tap into the existing sensor and tune it so it trips on at a certain voltage (that correlates to temp): http://www.madxj.com/MADXJ/technical/technicalfiles/DKadjThermoSwitch/thrmswth.pdf

Or a toggle switch.

[compu_85]

I'm planning on using a metal hose clamp to attach a temp sensor to the side of my receiver dryer. Early W126s used a temp switch on the RD to trigger the fans, so I would presume this is a valid setup. I'll set it to kick on at around 190*f which will kick the fans on to the low speed, then re-purpose the stock high pressure switch to kick the fans onto high speed.

This is the switch / sensor I bought http://www.amazon.com/gp/product/B00029J3ZW

-J

[sixto]

I don't want a manual toggle, I don't want it to run continuously with the compressor and I don't want to open the refrigerant system to add a high temp switch. Sounds like an external temp switch is the way to go. Questions is, at what refrigerant temp should the switch close? And what does that translate to in condenser fin temp? I guess I can take a thermometer to cars with aux fans and see at what temp the aux fan comes on. I was hoping for an established rule-of-thumb or range.

I guess I can use a temp switch like compu has but I don't know that 190*F at the condenser is an appropriate setpoint.

Sixto
87 300D