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How can I make AC pusher fan turn on sometime or always


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#1 Victro84

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Posted 25 September 2020 - 04:29 PM

I am at my AC wits end and hope anyone might know how to jump my pusher fan so it comes on either when the compressor comes on or anytime my radiator fans are on.

My pusher fan never comes on, even when temp gauge is touching top hash and coolant is boiling in hose. I have done everything to stop overheat: new CX racing aluminum radiator and electric fans with two new 185 thermosensors; new water pump; new thermostat, and cleaned/backflushed out system. Each improvement allowed the temperature to stay cooler longer but in the Florida heat running non stop AC the temperature just builds at stop lights and after a while I am touching the top hash.

My AC has been redone R134 and is ice cold with a new slightly larger might max compressor and other parts so I think it is overheating the car because the pusher fan never comes on and the condenser heat builds over time. Just a guess but since it is the last piece of the system not replaced or working I don't have a lot of options. My last option is to move from two 640 cfm fans to two spal 1064 cfm fans which might cool the radiator down more. I have grounded the pusher fan and know it works and is getting power it just never comes on on its own. Where can I jump the pusher fan ground too or maybe the relay so that it comes on?

Any advice appreciated.
78 280z 2jz, 85 928, 87 Starion, 85 supra 2jz, s2000





#2 TexasQuest

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Posted 25 September 2020 - 06:41 PM

Just jumper wire the pusher fan to the puller fans so they all come on at the same time.
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View PostJohnnyWadd, on 04 March 2010 - 10:01 PM, said:

my shaft was big i dont know what your talking about.

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#3 BuGG

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Posted 26 September 2020 - 12:08 AM

The stock fans push 3000cfm - 4000cfm so you need better fans.

What happened to your stock fans?

Edited by BuGG, 26 September 2020 - 12:08 AM.

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#4 tux

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Posted 26 September 2020 - 01:23 AM

Is that combined?  Spal fans don't even move that much

#5 BuGG

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Posted 26 September 2020 - 10:59 AM

View Posttux, on 26 September 2020 - 01:23 AM, said:

Is that combined?  Spal fans don't even move that much

Yes

A single Spal can move 1600cfm. Check their site.

But again what happened to the stock fans?
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#6 Victro84

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Posted 26 September 2020 - 12:50 PM

The first thing I did was jump the thermosensors in the radiator so both stock fans would come on at 185 and run all the time but it still overheated. I then replaced the radiator, but yes, these two twelve inch fans that came with it seem weak. Stated Air Flow Rate: >1130 CBM/Hr which I think converts to 665 cfm. I purchased two 12 spals that should moved 1328 each. I think I will try jumping the negative on the pusher to on of the radiator fan negatives. I still have the original fans but I think they are too big to fit on larger radiator but it sounds like I am on the right track since they seems to move a lot more air and its a tight space. I would rather jump around the fan relays, if anyone knows how to do that, which is my original question, instead of a long wire running around the radiator and subject to all that heat.

Edited by Victro84, 26 September 2020 - 12:52 PM.

78 280z 2jz, 85 928, 87 Starion, 85 supra 2jz, s2000

#7 croquest87

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Posted 26 September 2020 - 06:05 PM

Overheating with 2 fans running?
Car shouldn't be overheating that much.
Perhaps check your temperature with aftermarket gage?

Edited by croquest87, 26 September 2020 - 06:08 PM.


#8 tux

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Posted 26 September 2020 - 08:12 PM

How's the thermostat and water pump?

#9 Victro84

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Posted 26 September 2020 - 09:20 PM

The whole system is pretty much new and I have checked the temperatures all over the engine with a red eye temp gauge or whatever they are called. I ran it a while with no thermostat and it just took longer to warm up but still overheated. The water pump is new and it did make a difference, the new radiator made a difference. So now it takes much longer for the car to get to overheat running, but it has to be on the road, it wont overheat in my driveway just running. If I am moving the car temp will go down, it is 5 minute stop lights in Florida heat which makes me think that pusher fan and weak electric fans are the culprit.
78 280z 2jz, 85 928, 87 Starion, 85 supra 2jz, s2000

#10 mikec

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Posted 27 September 2020 - 02:40 AM

Have a "block check" done on the radiator coolant.  Basically, a turkey baster like thing is used to suck up a little coolant for a chemical test that looks for combustion byproducts in the coolant.  If any are found, that indicates problems internal to the engine: leaking/failed head gasket, cracked block, cracked head, head and/or block surface not dead-flat so the head gasket can't do its job.

What is the ratio of antifreeze to distilled water?  Too much antifreeze actually diminishes the heat capacity of the water.  Going beyond 50% antifreeze, in a hot area like Florida, is not a good idea.

Also, the stock fans run through the IGN fusible link and the ignition key input post.  Thus, anything that causes voltage loss in that circuit robs the fans of electrical energy.  If your dash voltmeter is below 13 volts on a warmed-up engine, your wiring is suspect.  Very common issue.  Doubling-up the wire from the IGN fusible link output to the ignition key input post helps a ton.

Horrible ignition timing leads to an over-hot combusion which taxes the cooling system.  Verify the centrifugal and vacuum advance are working properly.  Basically:
1: engine idling, warmed up: timing should be at 10 deg BTDC.  Now unplug the vacuum hose going to the distributor advancer mechanism.  If the timing changes, your vac hoses are not correct - there should be NO vacuum on the advancer hose at idle throttle position.

2: with the advancer hose still disconnected... plug the hose.  Check the timing as a helper revs the engine to specific RPMs:
2a: no extra timing at 1200 RPM.
2b: 10 degrees additional advance (total=20 deg BTDC) at 2000 RPM
2c: 33 degrees additional advance at 6000 RPM.
This is a test of the centrifugal advance mechanism (weights and springs) inside the distributor.

3.  If that passes, test the vacuum advancer unit.  Return to idle RPMs.  With a source of vacuum and a vacuum gauge (e.g. a MitiVac tool) apply vacuum and verify timing change:
3a.  0 degress at zero to 80 mmHg vacuum  (80mmHg is about 3.15 ihHg)
3b: 12 degrees of additional advance at 150 mmHg (5.9 inHg)
3c: 23 degrees of additional advance at 280 mmHg (11 inHg)
3d: apply some pressure - 2 to 10 psi - and verify the ignition timing RETARDs a few degrees.  Be very careful if you use an air compressor as the pressure source as they can easily overshoot 10 psi and might blow out the vacuum advancer diaphragm.  If you simply blow into a hose, you'll be lucky to generate 2 psi of pressure.  Note that many aftermarket parts stores sell a vacuum advancer unit designed for non-turbo 2.6 engines; these advancer mechanisms lack the boost retard capability and are BAD for StarQuests.

While doing this test, apply some vacuum and hold it steady.  If the vacuum bleeds off by itself, your distributor vacuum advancer unit has a leak and must be replaced.  It'll only get worse AND that leak leads to issues when boost pressure is present as the mechanism should RETARD timing under turbo boost.  A leaking advancer may not retard timing enough leading to pre-ignition/detonation and a hot burn.

Remove the plug and re-connect the distributor advancer hose when complete.

Running lean also leads to a hot combustion.  A dying fuel pump often struggles to maintain fuel flow volume and fuel pressure as the pump gets hot; that will lean-out the engine.  StarQuest ECUs don't have much ability to compensate for a dying fuel pump and they don't have ECU error codes for bad fuel pressure/bad fuel pumps.  Old, plugged fuel filters (yes, plural) also lead to fuel starvation issues.  There is the main filter in the engine compartment, a small screen above each fuel injector (inside the "injector cover" part of the throttle body, a cone-shaped plastic mesh at the fuel pump inlet, and a larger plastic mesh "sock" on the fuel pick pipe inside the fuel tank.  Best test is to simply attach a mechanical fuel pressure gauge to the fuel hose going into the throttle body or by getting a screw-in adapter to replace the Allen-screw hex plug at the top/rear of the injector cover.  Go for a drive... after a while, verify fuel pressure is 36 to 38psi when not on turbo boost; verify the pressure increases 1 psi for each 1 psi of turbo boost.  Don't run a hose from the engine compartment to the interior - that's dangerous.  If you don't use an electrical based sensor + pressure gauge, use a stack of washers stuffed between the driver side hood hinge and the hood to lift that corner of the hood a little.  Then you can fit a fuel pressure rated hose in the gap and duct-tape the gauge in front of the windshield.

The stock StarQuest cooling system should be able to maintain middle-of-the-temp-gauge temps for off-boost driving with only the primary fan running on warm/hot days.  On hot days, when driving uphill or with boost pressure (i.e. working the engine hard) the temps may climb a bit - triggering the second sensor which should make all 3 fans run.  Yes, the second sensor will run the secondary fan AND the pusher fan if the coolant temps get hot enough.  The A/C system engages both engine-side fans whenever the compressor is running; if the refrigerant temps get high enough (which happens on a hot day) then the A/C will engage the pusher fan too.

Look at the "hot side" (cast iron exhaust side) of the turbo after several miles of off-boost 40 to 50 mph driving... when your dash temp says the engine is running hot.  Pop the hood and quickly look at the turbo hot side.  If it appears to be glowing orange (easiest to see at night!) then your exhaust system is plugged and that's hurting the engine.  A dull glow is not uncommon... but a brighter orange glow is bad if you haven't been using significant amounts of turbo boost.  Typically, the catalytic converter gets plugged a bit.  After the engine cools, remove the "pre-cat" (the one bolted to the back of the turbo) and look inside it.  You should see a fine screen/mesh.  If that screen looks clogged... not good.  But not uncommon on high mile StarQuests especially those that have suffered turbo failures.  Turbo failures often allow engine oil in to the exhaust which clobbers the cats.

mike c.

#11 mikec

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Posted 27 September 2020 - 02:59 AM

In answer to your original question: if you ground the wire on the radiator temp sensor underneath the secondary fan, the secondary fan and the pusher fan should run.

Look at the refrigerant lines near the A/C receiver/dryer... you'll see a couple of electrical sensors in those lines.  One will have black and black+yellow wires feeding it (on the wiring harness side of the connectors; the wire colors from that connector to the sensor can be anything)... find it and unplug the electrical connector.  it'll be small with the plastic around the pins looking like a double-barrel shotgun.  Use a jumper wire to connect the wires on the harness side connector.  That simulates an a/c refrigerant pressure switch sensing high pressures which should trigger the pusher fan.  High a/c refrigerant pressures trip the sensor switch which turns ON relay A-24 to run the pusher fan.  A-24 is one of the relays on that bracket by the ignition coil... look for one with blue+black, black+yellow, black, and a fatter blue+yellow wire.  Test it by swapping it with the relay that has green+white, yellow+white, black+white, and blue+red wires (compressor clutch relay).

The secondary radiator temp sensor and the a/c high-pressure switch are actually wired in parallel... so either one should trigger the pusher fan and the secondary fan.  The a/c computer has a second pair of relays to trigger the engine-side fans (different from the relays triggered by the radiator temp sensors) regardless of coolant temp; thus both engine-side fans should run whenever the a/c compressor is ON.  This does NOT run the pusher fan though... that only engages if the radiator temp gets high and/or the a/c refrigerant pressures are really high.

You can re-wire the pusher fan relay (A-24) to trip/run whenever the a/c commands the engine-side fans to run regardless of refrigerant pressures.  Cut the harness blue+black wire (which is one of the relay coil wires) several inches away from the relay.  Tape the harness wire out of the way.  For the stub wire now coming from the relay: connect that blue+black wire to relay A-27s fatter blue+white wire.  This blue+white wire is grounded by A-27 when the a/c computer runs the fans; it is also pulled to ground by relay A-08 when the secondary radiator temp sensor trips.   Relay A-27 will be near A-24, look for a relay with green+white, black, fatter black, and fatter blue+white wires.  Moving this wire will make the pusher run whenever the a/c compressor is ON (regardless of refrigerant pressures) or when the radiator temp sensor trips.  Back to relay A-24: cut the blue+black wire, tape the harness wire safely out of the way.  Splice a new wire into the stub blue+black wire coming from the relay and run it all the way to the blue wire at either engine-side fan.  This changes the source of +12volts feeding the A-24 relay coil from the ignition switch ON position to the same source that runs the fan motors.  Basically, these wiring changes move A-24's relay coil to be in parallel with the secondary fan motor.

mike c.

#12 Victro84

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Posted 27 September 2020 - 07:55 AM

Your the best Mike C. I will need to read this about 750 times but thanks so much for the specific detailed directions and I am sure it will be useful to others in the future also. On a side note, what are your thoughts on bent fins reducing cooling on our 30 plus year old cars. Over time many of my intercooler fins have become bent and many of my AC condenser fins have become bent. Do you think this reduction in air flow from bent fins can contribute to a reduction in cooling ability of the system? Maybe it is just because I like to run the tach in Florida heat and it pushes the cooling system to the limit. But, that said, with the small air openings it just seems like the air has to get past a lot of obstacles to reach the radiator especially with so many bent fins. I am obviously going to do your step by step approach to find the source of my heat issues first because several of them shed light on some abnormal heat at the back of the engine and sporadic sputtering at 5 or 6k rpm. Really good stuff Mike C.!

Edited by Victro84, 27 September 2020 - 09:18 AM.

78 280z 2jz, 85 928, 87 Starion, 85 supra 2jz, s2000

#13 JAinsworth

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Posted 28 September 2020 - 05:18 AM

I don't see it mentioned but are your fans running in the correct way? Fans wired backwards will run that way and push/pull the air incorrectly and not through the radiator as intended.
Jimmy
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This is the factory vacuum line routing:

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#14 importwarrior

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Posted 02 October 2020 - 04:52 AM

FAQ replacement fan motor how too.

http://www.starquest...howtopic=135983

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#15 Victro84

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Posted 15 October 2020 - 06:51 AM

Overheating Saga Update: I found a parts Starion locally and not much left but grabbed the fan relay block. Got home and replaced the AC pusher fan relay and boom, the AC fan comes on when the compressor comes on, victory! The old relay was clicking but nothing was passing through, so never assume just because it clicks it works.

Still this was not enough to keep the car from gradually overheating so I picked the next most likely item on Mike C’s list. The catalytic converter. Temp at top was 50 degrees higher than temp at bottom of cat. Pulled and it was a mess the top mesh looked covered up and bottom had melted hole, I don’t know how any gases got through it. Replaced with CXRacing downpipe and new bosch oxygen sensor and removed the secondary air cleaner and pipe assembly that was part of old cat setup. Took car for a test drive and ran it hard for about 20 minutes hitting some long stop lights with AC on the whole time. An engine sputter I had at 5k rpm disappeared, which I assume was that clogged cat back pressure. It was not a particularly hot day but as before the temp continued to build at stop lights to between top and mid hash, closer to top, but at least I now had a gap and was not touching top hash now, so the cat change helped.

I took red dot temperatures at idle in my driveway and everything was over 200, radiator, thermostat housing, rear of engine was hotter more like 220-230. Turned off AC and it took about 15 minutes at idle for the system to bring the temp down to mid hash and 190s. The car would not cool down at idle before so somewhat of a victory but still taking way too long so I am assuming those fans are not pulling enough air to cool down that radiator. My experience with a different car, but I have one SPAL fan on my Supra aluminum radiator with a digital dash temp and when it hits 189, I can hear the fan come on and the temp drop to 185 quick. It maintains a 5 degree variation but my starion lets temp up over 200 and needs 15 minutes at idle to bring down the temps, so something is still wrong. I got some SPAL fans to replace the 12 inch electrics that came with cxracing aluminum radiator to double CFM flow which is my next step. It is a possibility that when I connected the cxracing fans blue wire to the stock fan blue wire that I wired them backwards and the fans are pushing not pulling so I will double check before or when I complete the fan switch.
78 280z 2jz, 85 928, 87 Starion, 85 supra 2jz, s2000




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