Clutch Fan Problem

[Kilby]

Once in a while, my AC won't blow cold air when I first start the truck up or if the truck is sitting still but idling. Like in a drive-thru. We've come to the conclusion that the culprit is the clutch fan itself. It's barely spinning and not cooling the AC condenser. After the truck runs for 10 minutes or so, the fans clutch will finally engage, the condeser will get cooled and the AC starts blowing cold air again. Yesterday when tinkering with this, the AC compressor released some freon through it's pressure relief valve which indicates too much pressure build up on the compressor itself because of the overheat issue at the condenser.



Anyone know if there is a switch or sensor that tells the clutch fan when to engage? Any known TSB's on something like this? TIA.

 

[bmoeller]

Anyone know if there is a switch or sensor that tells the clutch fan when to engage? TIA.

I believe so. Works like a Horton fan.



There is a high pressure switch, along with a low pressure switch. Both are to prevent damage to the compressor. High psi from overcharge or plugged componet, low psi from low charge.

 

[Kilby]

Actually I was wondering about a switch for the clutch fan, not the AC compressor. I don't know what a Horton fan is. Is Horton a type of fan or company name?

 

[RBender]

Maybe this will be of help:

The Engine Control Module (ECM) controls the level of engagment of the electronically controlled viscous fan clutch by monitoring coolant temperature, intake manifold temperature, and air conditioning status. Based on cooling requirements, the ECM sends a signal to the viscous fan clutch to increase or decrease the fan speed.

If you think that it might be a problem with the viscous fan clutch:

If the fan assembly free-wheels without drag (the fan blades will revolve more than five turns when spun by hand), replace the fan drive. This spin test must be performed when the engine is cool.

 

[Boonieman]

I do know that on my truck the fan doesn't automatically engage just because I turn on the A/C like some cars do. I also know that the compressor relief valve should never lift because the compressor hi cutoff switch should prevent that before the pressure ever gets that high. The first place I'd start is hooking up some refrig gauges to see what your suction/discharge pressures are running and take some of the guesswork out of it. I don't remember off the top of my head what the pressures should be, but that ought to be pretty easy to find out. I would be surprised if the fan clutch is the issue.

 

[rbattelle]

Hopefully Matt400 will read this thread, as I know he's been working very hard on figuring out the ECM fan signaling.



The ECM can detect a fan speed that is too high or too low compared with the demand speed. So if you're not setting any codes, the computer must think the fan speed is just fine. That could mean a faulty fan speed sensor, or perhaps a faulty coolant temperature sensor. Not sure if these sensors could fail and not set any codes.

 

[Boonieman]

rbattelle:



I know one of the things that can cause those symtoms is a fan clutch, but it's the freon (SUVA) relief valve thing is what bothers me and makes me think it's in the HCO switch for the compressor. If it was the fan clutch, or the ECM control of the fan clutch wouldn't the compressor just shut down due to high discharge pressure and stop the cooling? I also believe that the HCO switch goes thru the ECM, but I'm not positive. Do you know if that's correct or not?



Danny

 

[rbattelle]

You're right, of course, Danny. I agree that the compressor should shut down if the pressure gets too high, but Kilby did comment that once he cools the condenser down then the A/C begins to blow cold again. That might suggest that the compressor is shutting down, and the little "burp" of refrigerant that he heard was the compressor "testing the waters", so to speak. It found pressure was too high and immediately shut off again. Or maybe it wasn't even running but the temperature in the condensor got so high it triggered the relief valve on it's own.



If that's right, then Kilby is correct to look toward the engine fan for the solution to the overheating condensor. I'm no HVAC expert, so I could be all wrong.

 

[Boonieman]

Very good points. I was thinking the relief valve is set for around 400#, quite a bit above the high cut out setpoint. Heck, I'm no expert on auto HVAC either but I hope we hear what the cause is.

 

[EB]

I was having the same problem with mine. It was the fan clutch. If your engine is at operating temp and you kill it, your fan should be locked up if you try to turn it by hand. I replaced the fan clutch and have had no problems since. This happened at about 134k miles.

 

[sag2]

If you have a California 03 or 04, there is a flash that will take care of it. The fan does not engage until the coolant hits about 130 degrees. If you fire it cold and turn on the A/C, the clutch will start to cycle when the head pressure hits the cut out at about 470 PSI. This takes a couple of minutes depending on ambient temp. If the truck moves at all, the air flow will keep the condenser cool enough to work.

The short answer is the flash makes the fan work with the A/C on regardless of coolant temp, and it works great I might add.

 

[Kilby]

You're right, of course, Danny. I agree that the compressor should shut down if the pressure gets too high, but Kilby did comment that once he cools the condenser down then the A/C begins to blow cold again. That might suggest that the compressor is shutting down, and the little "burp" of refrigerant that he heard was the compressor "testing the waters", so to speak. It found pressure was too high and immediately shut off again. Or maybe it wasn't even running but the temperature in the condensor got so high it triggered the relief valve on it's own.



If that's right, then Kilby is correct to look toward the engine fan for the solution to the overheating condensor. I'm no HVAC expert, so I could be all wrong.

Sorry for not keeping up with the thread guys. I thought I was subscribed to the thread and no one was responding.



Anyhow, rbattelle is right. The compressor should shut down if the pressure is too high but the compressor would cycle off and on quickly. It would see the high head pressure and shut off again. The PRV did it's job by dumping the excess pressure off the head of the compressor.



I've never been trained in AC but since I deal with compressors all day long, I kinda tend to learn more than I care to know, so I have a good idea how AC systems work. However, my father-in-law has been a Ford AC specialist for over 20 years but now currently works for me. He nailed the problem immediatly once he saw truck first hand when it wasn't cooling down.



I think EB has confirmed my problem and sag2 and RBender are onto the fix. Now all I gotta do is explain this to the service guys and hope they do something about it. Heh heh! Thanks to everyone!

 

[rbattelle]

Kilby needs to get this fixed so he can get back to working on the on board air system.

 

[Kilby]

Ha! I'll have you know that we worked on the OBA stuff most of the day yesterday. Turns out DC not only changed the fan shroud mounts but they also shortened the inner cooler tube a bit. I assume the '04. 5 600's have a larger turbo on them, making the inner cooler tube shorter. No?