Tazman

Hey Folks,

Just had my AC recharged after a block (53) swap, more on that later.

Service tech warned me against using the AC until I replaced the fan clutch. Claimed it was free wheeling at idle and not developing enough flow across the conndenser, ultimately causing excessive system pressure.

Is there a good test for the fan clutch without removal?? Seems my brother's 96, Dad's 2001 and buddy's 98 all free wheel even after reaching operating temp.

I'm sure just getting the temps up are not enough at idle and will it really "lock up" or just be stiffer?

Anybody know the nut size off-hand?? I believe it's a lefty as well right??

If I have to remove, I'll hold over my corn roaster with a thermometer and see if she locks up/changes in any way around 100 c.

Thanks for info

CTD NUT

It takes a lot of heat to get that clutch to lock up completely......I have noticed that the heat off the condenser alone, may not be enough to kick on the clutch to full lock - the rad temp still needs to be hot enough in conjunction with the condenser temp to lock up all the way. I had a tech tell me my clutch was smoked too but I happened to know that it is working just fine! With the hood up and idling, the engine just won't throw off enough heat. Close the hood, put the truck in drive and load the motor up to 1500 rpm with the AC on......I'll be willing to bet the clutch will kick in.

CoastalDav

The only time I ever hear my fan clutch is when I'm towing the trailer having just come off the interstate, traffic light to traffic light. It does go away between lights as you get RPM's up.

Thats normal carrying the heat off the hyw with less air flow in town untill it cools down some.

You did make a interesting point with the fan clutch issue related to the A/C unit and the high pressure thing. I've replaced the compressor in this truck two times since new. Thats two failed units working on the third. I guess you check the high side easy enough with a set of gauges if you know whats normal and whats not at Idle.

Dave

infidel

The fan clutch is easy to check.
With the engine off give it a spin, you should be able to turn it but it shouldn't freewheel.

Tazman

I understand what you say Bill,

No, it won't "free wheel" as such. There is a light resistance and I would expect that to increase as temps rise until full lock.

So, do I understand you correctly then, if there is some sort of resistance all is well??

At normal operating temp, I would say it takes 5-7 seconds for it to come to a standstill after engine shutdown.

Normal??

CTD, agreed.

The tech wasn't disputing whether or not there was enough heat for the clutch, he was concerned that not enough air was being pulled across the condensor @ idle. High pressure was the result to the extent they shut it down. I believe it was 400 psi???

One would conclude that at any point in time the AC system would be protected (enough air flow) They were able to create a condition that indicated otherwise. (clutch smoked)

I wonder if these systems are designed for higher pressures like 420 psi...

All I know is things worked fine prior to the block swap.

CTD NUT

I would say that would be normal if the air off the rad wasn't too hot.....that is about how long my will take to slow down if the motor wasn't working too hard before the shutdown.

Haulin_in_Dixie

A fan clutch is $69 at an Advanced Auto Parts. Cheange it and let you mind be at ease. Mine is doing the same thing at idle when I is real hot. This can also be caused by moisture in the system that leaves the dryer when real hot then plugs the capilary tube. I even put the larger fan on mine and it does not stop it.

I will give you something to try, when you are coming to an area where you slow down, put it on recurculate and see if that helps. Mine will keep on working on recirc.

The nut can be turned with a cresent wrench with one of the bolts removed for clearance. It is left hand turn, you do not have to tighten it tight. A big pair of pumps will hold the pully hub. Take the fan assembly out towards the passenger side and up, it will fit, tight but fit.

J BODY

The viscous fan clutch will never know the a/c is on or off, and they aint rocket science. Some lock up faster than others (thus more often). If you want to know if it will engage take a piece of cardboard and slide it down in front of the radiator. Sitting, a/c off, run the rpms up 1500-1800 rpm and wait....generally when the gauge gets a little over the 1/2 mark you'll start hearing the "jet take off" as the clutch starts locking up. You will hear it. On my old gasser I installed a fan clutch from a customers truck. His complaint (ongoing) was that the clutch locked up too often. It did lock up more than mine and it worked great for towing my trailer and helped the a/c in town too. The "new" trucks fan clutch have a speed sensor on them as well as a pcm controlled valve so the fan can actually be operated by the pcm. These use a/c as an input so it will increase the duty cycle of the valve in the clutch fan to increase air flow to help the a/c cool.

CZSteve

Not meaing to highjack this thread. But, wondering if the clutch might be related to AC effeceincy @ idle.

My AC blows EXTREMELY cold while running @ speed, but if I'm sitting @ idle it not near as cold.

Is that an indicator of being low on refrigerant or possible a bad fan clutch?

J BODY

No that's a sign of normal operation CZSteve. That is one of the advantages of the new trucks as the pcm can engage the fan when it sees the a/c clutch input. Even on the Hemi equipped trucks they have gone to a separate a/c condensor off to the side of the radiator with its own electric fan. Keeps the a/c much cooler when the truck isn't moving. You could even go one step beyond this and make a "spray bar" to run water over the condensor to aid in cooling.

HOHN

Just so no one's confused, a viscous fan clutch will NEVER lock up 100%. Just like it can never freewheel completely (when not needed), it can never lock up completely when needed.

It's really the worst of both worlds.

This is why so many of us run fanless in the winter. It really does reduce the warmup time of the engine, as the fan still turns when cold, and this robs precious heat from the engine when it's really cold.

By the way-- those of you considering an electric fan conversion are in for a rude awakening when trying to find one that moves enough air.

The stock fan moves on the order of 2600CFM!

caper

Am I missing something, cant understand how the fan slows down warm up time in winter ? Untill the thermostat opens the fan has no effect on the temp only the heater core fan does , If you have that on high the truck will take longer to open thermostat and get the truck to the 190 mark.But once the truck hits 190 the trermostat opens and your usually drivin down the road by this time and theres all that air going through the rad, fan or no fan.

J BODY

.....of course there is the Horton fan clutch option. Pretty spendy, but would be nice to lock the clutch with the flick of a switch.

HOHN

It's not the radiator-- it's the fan blowing bitter cold air against the block.

I can't tell you exactly WHY it is the case, but running fanless DEFINITELY let my truck warm up faster in cold weather.

jlh

killfast1

It only moves that much air when fullly engaged. So If you were to use a couple of electric fans you could have them set for a little lower temps to help compensate for the amount of air also.

Dont you think?



What about this one? It moves 2700-4600 CFM
http://www.flex-a-lite.com/auto/html...-electric.html