ckuske Posted April 19, 2023 Share Posted April 19, 2023 I'll start by saying this... I know better now. I bought and installed a Severe Duty Fan Clutch (Four Seasons 36704) for my truck when it was running hot when I first bought it back. I've barely driven it since then, but hope to ramp up. When I got my A/C done yesterday, the guy said "your fan clutch acts weird, it never really kicks in". I told him that I had noted the same thing, but didn't really have anything to compare it to. The behavior is this: When started cold, the clutch is engaged. There is lots of airflow. After about 60 seconds, the clutch disengages. The issue is even when the truck is fully warmed, it never really seems to meaningfully re-engage. This is only at ~70F ambient, so that may be the issue. The clutch isn't shot, I can barely move the blades more than a few inches when everything is cold. The fan clutch currently installed is is a severe duty model... at the time I assumed "severe is better than heavy, so why not?". I was naive, didn't know to check part numbers, the MPC, etc. Now going to Rockauto, the Heavy Duty has a match to the part number in the MPC. Am I correct that having the severe duty clutch installed sets a higher threshold to lock up maybe? I read that a severe duty will lock up harder than a standard or heavy, but it didn't mention the threshold to lock up, only the amount of clutch lockup once it is engaged. (https://www.rockauto.com/genImages/93/4s410-fan-clutches-standard-heavy-severe.pdf) This seems to be a better fit (https://www.rockauto.com/en/moreinfo.php?pk=815302&cc=1121443&pt=6812&jsn=1735), but I want to make sure I can expect different behavior. The other option is that I just haven't driven it in hot enough weather yet? But, I want cool air to be pulled in to help cool the A/C condenser. Thoughts? Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 19, 2023 Share Posted April 19, 2023 I don't know what fan clutch is on Big Blue. But I do know that when the engine is started at cold temps the fan does what yours does - engages for maybe a minute. Then it disengages and doesn't come back in unless the coolant temp gets pretty warm. But I don't know what "pretty warm" really is. Link to comment Share on other sites More sharing options...
ckuske Posted April 19, 2023 Author Share Posted April 19, 2023 I don't know what fan clutch is on Big Blue. But I do know that when the engine is started at cold temps the fan does what yours does - engages for maybe a minute. Then it disengages and doesn't come back in unless the coolant temp gets pretty warm. But I don't know what "pretty warm" really is. Glad to hear you see the same behavior! Since there is no feedback from the coolant temp sensor to the fan clutch, the fan clutch must be engaged by the ambient temperature inside the engine compartment, correct? I'm sure outside ambient temp factors in as well. It's supposed to be warmer here this weekend, perhaps I'll see different behavior. Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 19, 2023 Share Posted April 19, 2023 Glad to hear you see the same behavior! Since there is no feedback from the coolant temp sensor to the fan clutch, the fan clutch must be engaged by the ambient temperature inside the engine compartment, correct? I'm sure outside ambient temp factors in as well. It's supposed to be warmer here this weekend, perhaps I'll see different behavior. It is the air temp that is passing the clutch, so is surely influenced by ambient temp as well as the coolant temp. Maybe you'll see it work this weekend. Link to comment Share on other sites More sharing options...
grumpin Posted April 19, 2023 Share Posted April 19, 2023 Glad to hear you see the same behavior! Since there is no feedback from the coolant temp sensor to the fan clutch, the fan clutch must be engaged by the ambient temperature inside the engine compartment, correct? I'm sure outside ambient temp factors in as well. It's supposed to be warmer here this weekend, perhaps I'll see different behavior. The 86 I used to own did the same thing and had to be pretty warm out for the engine to get warm enough to engage it. Link to comment Share on other sites More sharing options...
mat in tn Posted April 19, 2023 Share Posted April 19, 2023 The 86 I used to own did the same thing and had to be pretty warm out for the engine to get warm enough to engage it. the temp that the coil on the fan clutch reads is the issue. in normal operation it is reading ambient air and a bit of heat from the condenser. it really only senses a large volume of heat when the t stat opens and fills the radiator with hot coolant, that's when the surge should happen. and the clutch start driving the fan more forcefully. it is a bit of a delayed reaction being that the coil must absorb enough heat to adjust the valving of the fan clutch. this is why modern cars like the dodge ram use a separate electric fan for the condenser exclusively. adding a pusher fan controlled by a relay off the compressor will be the best a/c performance without loading up the engine with a heavy fan. I am using both versions at this time and the electrics are doing well. Link to comment Share on other sites More sharing options...
ckuske Posted April 20, 2023 Author Share Posted April 20, 2023 the temp that the coil on the fan clutch reads is the issue. in normal operation it is reading ambient air and a bit of heat from the condenser. it really only senses a large volume of heat when the t stat opens and fills the radiator with hot coolant, that's when the surge should happen. and the clutch start driving the fan more forcefully. it is a bit of a delayed reaction being that the coil must absorb enough heat to adjust the valving of the fan clutch. this is why modern cars like the dodge ram use a separate electric fan for the condenser exclusively. adding a pusher fan controlled by a relay off the compressor will be the best a/c performance without loading up the engine with a heavy fan. I am using both versions at this time and the electrics are doing well. I'll let it be for now and see how it behaves as it warms up. I just wanted to verify this sort of behavior is typical. Thanks all! Link to comment Share on other sites More sharing options...
85lebaront2 Posted April 20, 2023 Share Posted April 20, 2023 I'll let it be for now and see how it behaves as it warms up. I just wanted to verify this sort of behavior is typical. Thanks all! On Darth, the original fan clutch would be on at a cold start then drop out, AC on in summer would bring it on, heavy traffic, slow moving in the summer with AC on and hauling a 30 ft 5th wheel. Leaving a stoplight would give me a roar like one of NASA Langley's wind tunnels up to around 40-45 mph, at which point it would start tapering off. Link to comment Share on other sites More sharing options...
ckuske Posted May 5, 2023 Author Share Posted May 5, 2023 On Darth, the original fan clutch would be on at a cold start then drop out, AC on in summer would bring it on, heavy traffic, slow moving in the summer with AC on and hauling a 30 ft 5th wheel. Leaving a stoplight would give me a roar like one of NASA Langley's wind tunnels up to around 40-45 mph, at which point it would start tapering off. I got it hot enough today. It definitely works! The wind really kicked up with very hot air, and the temp gauge dropped a little bit after that... Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted May 5, 2023 Share Posted May 5, 2023 I got it hot enough today. It definitely works! The wind really kicked up with very hot air, and the temp gauge dropped a little bit after that... That's really good to hear, Chris! I too have a Four Seasons severe duty fan clutch. It seems to work well IME. Link to comment Share on other sites More sharing options...
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