Should Cooling Fan Come On When AC Is On? - Focus Fanatics

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johnishere J Hey All, Can someone answer for me: [2002 Focus SE wagon, 2.0 Zetec] I'm having an engine overheating issue, and cooling fans are not turning on (I think). My question is: When I turn on the AC, do the engine cooling fans turn on immediately, or is it still engine load/temperature dependent (meaning that cooling fans don't turn on immediately after you turn the AC on, but rather only turn on after the car warms up or the radiator/condensor heats up)? [I've seen it mentioned that the engine cooling fans should come on when the AC is turned on, but it did not specify whether they should come on right away.] [I've already tested the fan fuses and relays, and fan motor for operation - all are good and fan motor works with 12VDC applied directly. The cooling fan resistor measures .25 ohm, which is typical according to specs - but I would need to test it further before ruling it out. I have not tested the temperature sensor yet.] Thanks much. #1 · Aug 11, 2019 (Edited) Hey All, Can someone answer for me: [2002 Focus SE wagon, 2.0 Zetec] I'm having an engine overheating issue, and cooling fans are not turning on (I think). My question is: When I turn on the AC, do the engine cooling fans turn on immediately, or is it still engine load/temperature dependent (meaning that cooling fans don't turn on immediately after you turn the AC on, but rather only turn on after the car warms up or the radiator/condensor heats up)? [I've seen it mentioned that the engine cooling fans should come on when the AC is turned on, but it did not specify whether they should come on right away.] [I've already tested the fan fuses and relays, and fan motor for operation - all are good and fan motor works with 12VDC applied directly. The cooling fan resistor measures .25 ohm, which is typical according to specs - but I would need to test it further before ruling it out. I have not tested the temperature sensor yet.] Thanks much. Sort by Oldest first Oldest first Newest first Most reactions #2 · Aug 12, 2019

johnishere said: Hey All, Can someone answer for me: [2002 Focus SE wagon, VIN type 3] I'm having an engine overheating issue, and cooling fans are not turning on (I think). My question is: When I turn on the AC, do the engine cooling fans turn on immediately, or is it still engine load/temperature dependent (meaning that cooling fans don't turn on immediately after you turn the AC on, but rather only turn on after the car warms up or the radiator/condensor heats up)? [I've seen it mentioned that the engine cooling fans should come on when the AC is turned on, but it did not specify whether they should come on right away.] [I've already tested the fan fuses and relays, and fan motor for operation - all are good and fan motor works with 12VDC applied directly. The cooling fan resistor measures .25 ohm, which is typical according to specs - but I would need to test it further before ruling it out. I have not tested the temperature sensor yet.] Thanks much. Click to expand...

On my 2002 SE wagon Zetec 5-speed the low speed fan runs as soon as I turn on the AC - even if the engine is cold. Interestingly if I turn off the AC and the engine is still cold the fans will continue to run for about 30 seconds before shutting off. The fan relays control the fans and the PCM controls the relays. The PCM is signaled from the HVAC control unit in the dash. Paul #3 · Aug 12, 2019 That helps me out. Thanks much. (The 30-second run-out time makes sense. Just because you turn off the AC, the AC condenser is still likely to be warm or hot.) Show more replies 0 Reply #8 · Aug 15, 2019 (Edited) REPLACE the relay, you can have one that works and tests fine all day long and then when it gets just right it does not come on when needed. If you test 100 times OK and it does not come on at 102 then it is still bad. Relays are cheap and silly to melt down a car over one. My '02 the fan comes on with a/c in summer but does NOT with a/c in winter, I've driven for as long as an hour before it comes on and no issues at all. That is with an indicator light wired into the power to fan. I have one on high and low as the cooling electrics are commonly what send the cars to the scrapyards. FYI, PCM activates high fan around 230 F. or over 270 psi highside pressure with a/c on. Low fan on at 220 F. and a/c on; both numbers can vary by 5 degrees and even at each application. #9 · Aug 15, 2019 (Edited) I finally just now had the time to drive this thing around for awhile. And of course, nothing happening.... Meaning temp gauge right where it's supposed to be, although no fans either. As far as the relay is concerned, I've never been a fan of "diagnosis by maybeology": 'maybe' it's bad even though it tested ok out of circuit, or 'maybe not'. The relay is easy enough to bypass test (can even do it live while driving) to determine if it's the relay or not. Besides, if it was working 100 times - or even once in my case - before failing then I'd be ok to replace it on a guess that it might be intermittent. But in this case, the relay doesn't seem to be turning on ever - so before I replace the relay I'd like to know whether the relay circuit is getting a signal from the PCM. For me to believe that the relay tests perfect every time I test it 'out' of circuit, but then that it just happens to be failing at exactly the same time that I put it back 'in' circuit, AND that it then just happens to start working again exactly when I disconnect the CHT sensor.... it would take a whoooole lot of vodka for me to believe in that much of coincidence. I managed to locate some specs for the CHT sensor (resistance/voltage specs), so when I have some more time tomorrow I'll probably test it to confirm whether it's bad. The relays have proven to be working at least during testing. However, the CHT sensor has proven that when it's connected the fans don't work; when it's not connected the fans work. So, although that is not conclusive, it does confirm that the PCM, wiring, relay, fuses, fan resistor and fans are working (generally speaking) - so therefore between the relay and the CHT sensor, it would be more likely lean toward being a bad sensor in this case. Yep, I also planned on likely putting in a couple of indicator lights for the fan operation (after I get things working) until I've regained some confidence in the car again. I do appreciate the input and the info. Show more replies 0 Reply #10 · Sep 15, 2021 (Edited) Hi, I don't think so. I own a car myself (an old Triumph GT6 in good condition). Of course, I haven't asked myself such a question yet. Although based on my knowledge in that area, I am guided by this. I think my answer has a place to be. Although I had another problem with air conditioners. Somehow it started to go wrong with me. I thought. that the car broke down, and I wanted to sell it, but then I turned to a wonderful service that helped me fix this problem: Reliable Aircon Chemical Wash in Singapore At Cheap Price - Marvellous Aircon Servicing Singapore . It turned out that the air conditioner was just clogged. #11 · Apr 10, 2023

johnishere said: Hey All, Can someone answer for me: [2002 Focus SE wagon, 2.0 Zetec] I'm having an engine overheating issue, and cooling fans are not turning on (I think). My question is: When I turn on the AC, do the engine cooling fans turn on immediately, or is it still engine load/temperature dependent (meaning that cooling fans don't turn on immediately after you turn the AC on, but rather only turn on after the car warms up or the radiator/condensor heats up)? [I've seen it mentioned that the engine cooling fans should come on when the AC is turned on, but it did not specify whether they should come on right away.] [I've already tested the fan fuses and relays, and fan motor for operation - all are good and fan motor works with 12VDC applied directly. The cooling fan resistor measures .25 ohm, which is typical according to specs - but I would need to test it further before ruling Click to expand...

johnishere said: Hey All, Can someone answer for me: [2002 Focus SE wagon, 2.0 Zetec] I'm having an engine overheating issue, and cooling fans are not turning on (I think). My question is: When I turn on the AC, do the engine cooling fans turn on immediately, or is it still engine load/temperature dependent (meaning that cooling fans don't turn on immediately after you turn the AC on, but rather only turn on after the car warms up or the radiator/condensor heats up)? [I've seen it mentioned that the engine cooling fans should come on when the AC is turned on, but it did not specify whether they should come on right away.] [I've already tested the fan fuses and relays, and fan motor for operation - all are good and fan motor works with 12VDC applied directly. The cooling fan resistor measures .25 ohm, which is typical according to specs - but I would need to test it further before ruling it out. I have not tested the temperature sensor yet.] Thanks much. Click to expand...

my 2012 started with fan not working so I changed the fan module located on the fan and changed the relay. Then week later car over heated fan not working I changed module & thermostat and bypass hose from rad to pressure tank to intake. New coolant 5 hrs later fan don’t come on when ac is turned on engine temp normal so I don’t know if it will work either, tomorrow I’m installing a Hayden adjustable thermostat also going to wire in a relay for the ac when using it will turn the fan screw ford and their crack smoking engineers. Bastards just can’t build things simple to work well, #12 · Apr 10, 2023 The add-on Hayden temp sensor will simply screw the computer up. The computer looks to the original setup for timings to bump the idle up as needed when the fan comes on to keep the engine from dying, you won't have any of that using the other temp sensor setup. Be ready for erratic idle and possible engine dying when car is sitting at say a stoplight. The fan coming on is quite an amp hit to power and why the computer bumps idle up just before the fan gets power, that smoothes the idle out. BTDT. You will also need a whopping relay as the low speed is typically 30 amp and the high 50. And bigger than normal wire gauge (10 gauge) to cover the amp requirement of the direct power lead to fan. My setup worked fine but not having the computer bump the idle became intolerable during the summer when the fan comes on a lot. The cars tend to vibrate heavily when a/c comes on and lowers idle with no bump-up and it did doubletime on mine until I quit that setop. #13 · Apr 10, 2023 I am aware of that I’ll be using a cut out relay when the ac is on or the temp switch activates the system, my idle is only slightly rough nothing I can do because everything’s been changed twice that controls the fan, #15 · Apr 17, 2023 Yes the cooling fans automatically come on when ac is turned on. As well as when the temp sensor reaches he’s a certain temp they come on. I’ve got a 2012 I replaced the relay the temp sensor and the computer board on the fab 2 x , I’m hooking up adjustable thermostat & a bypass jumper to the ac compressor that turns off the adjustable stat when in, tired of dumping money into a car designed by engineers with a drafting pencils in one hand and a crack pipe in the other hand, #16 · Apr 17, 2023 Actually the PCM will stop fans from coming on at all in the colder months. I have lights on both low and high on mine and they will often not come on for a month in winter. The a/c compressor won't either even if turned on. The computer knows when to let them work. #17 · Apr 18, 2023 But if everything makes the fans work besides the computer suck the fans ain’t gonna work 0 Reply #18 · Apr 18, 2023 Uh, YOUR fans ain't gonna work, by your own mouth. Others are doing fine. You might oughta look closer at that. #19 · Apr 18, 2023 Got the grammar police here 0 Reply #20 · Apr 19, 2023 I was college exit english in the 7th grade. Just playing to the level. Seriously............you just haven't found the problem yet, but get mad and then never find it? That forbodes ill for the future. Changed wiring yet? The relay socket can easily do it. #21 · Apr 19, 2023

amc49 said: I was college exit english in the 7th grade. Just playing to the level. Seriously............you just haven't found the problem yet, but get mad and then never find it? That forbodes ill for the future. Changed wiring yet? The relay socket can easily do it. Click to expand...

My focus works perfect now. But college English exit in the 7th grade is not going to fix your car. Btw the sell really loud air horns on Amazon if nobody could here you blowing yours. 0 Reply #22 · Apr 19, 2023 Whatever........ To post #20.........fans will come on low in summer when a/c is turned on, unless a/c highside is over 270 psi, then they will be on high. Insert Quotes Post Reply

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