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this blows?


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14 replies to this topic

#1 gbianchi

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Posted 03 January 2008 - 11:30 PM

OK I have searched for info on this but didn't find an answer, what would cause both fans to come on immediately when using any of the 4 buttons that involve the ac compressor ac,acmax,def/heat,def. This was done on 2 90 legacys both at operating temp in the driveway on a 35degree day, on the 1st I can use these bottons and the fans do not come on right away or at all depending on temp, when they come on they cycle on/off as needed. On the 2nd the fans come on right away and stay on untill I choose a mode that does not use the compressor, the status of this AC system is unknown at this time(to cold to know) but the the compressor does run. Status of 1st AC is A. O. K. So who has the malfunction? 1st or 2nd, me thinks 2nd:dead: Thats about it for info any Ideas

#2 grossgary

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Posted 04 January 2008 - 01:17 AM

i agree, sounds like the second one has issues. it sounds like the dedicated radiator fan is stuck "on". i think this usually means the thermosensor (i believe it's the only electrical gizmo that is screwed into the radiator - usually the lower passengers side i think?), anyway usually this thermosensor is bad or the contacts/electrical plug are just dirty. or the associated relay is shot/sticking.

or the previous owner hard wired it.

should be an easy fix, good luck!

#3 keltik

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Posted 04 January 2008 - 04:34 AM

If its a model with air con, check the compressor is actually spinning up when you stick the A/C on. Im fairly sure one of the failure modes is to have both fans run constantly, as thats what you get with the ignition on and engine not running.

If the compressor is spinning - do you actually get cold air? Im willing to bet its a malfunction with the A/C compressor sensors or control rather than a fan relay issue.

On the 1990 Legacy im working on: the first fan will spool up immediately and the second one kicks in a second or 2 later. Both will run constantly if the compressor doesnt spin (engine off or drive belt missing).

#4 WAWalker

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Posted 04 January 2008 - 02:38 PM

The problem is with car #1.
I'm going to quote from the FSM in order to avoid confussion and argument.

From the Air conditioning system section.

MECHANISM AND FUNCTION

1) When MODE switch is set to "MAX A/C", "A/C", "DEF/HEAT" or "DEF", air conditioning sytem relay activates to enter a signal into engine control unit. This turns on both compressor clutch and F.I.C.D. (Fast Idle Control Device). At this point, the main and sub fans also operate. Blower relay operates to direct the air flowrate determined by FAN switch position.
2) Thermostat activates to stop compressor clutch, F.I.C.D., and main and sub fans.
3)When "High-Low" pressure switch operates, compressor clutch and F.I.C.D. stop but main and sub fans are operating.
4) When fan control switch operates, both main and sub fans operate rapidly.

#5 keltik

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Posted 04 January 2008 - 03:04 PM

The problem is with car #1.


I agree with all that from the FSM, but from what i read the problem was that the fans ARENT cycling on and off on car #2. As i dont have an FSM, does it say anything about that issue?

#6 WAWalker

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Posted 04 January 2008 - 03:48 PM

The system is designed to run both fans when the A/C compressor is running.

When in any defrost mode, the A/C is used to dry the air to prevent windsheild fogging. The A/C compressor runs, the fans run. If not there is a problem.

When in any A/C mode, the A/C is used to remove heat from the air inside the car. The A/C compressor runs, the fans run. If not there is a problem.

#7 gbianchi

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Posted 04 January 2008 - 06:17 PM

Thanks guys, I'll back the worry truck up and just go with the flow, err blow
g.

#8 brus brother

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Posted 04 January 2008 - 06:33 PM

Thanks guys, I'll back the worry truck up and just go with the flow, err blow
g.

Step away from the tool chest.:dead:

#9 gbianchi

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Posted 04 January 2008 - 07:13 PM

O K new question, do/are the fans come on without the engine/ac compressor running, as in just the key on, 1st car no 2nd car yes.....boy is this fun, good thing its raining cats and dogs
g
oops my bad, keltik allready mentioned the key on fans on..........so whats the problem item.

#10 WAWalker

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Posted 04 January 2008 - 07:23 PM

O K new question, do/are the fans come on without the engine/ac compressor running, as in just the key on, 1st car no 2nd car yes.....boy is this fun, good thing its raining cats and dogs
g.


Yes they should come on KOEO, with controls set to A/C or defrost mode.

In the post were I quoted from the FSM, read #1.

When you set the controls to an A/C or defrost mode, the ECU turns the fans on.

Car #1 is not right.

Car #2 is doing what it was ment to do.

#11 gbianchi

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Posted 05 January 2008 - 05:07 PM

O K, thanks for the input, this time I will just not tear anything apart, all though I'd like to.:horse:
g.

#12 gbianchi

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Posted 05 January 2008 - 05:16 PM

message deleted

#13 WAWalker

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Posted 05 January 2008 - 05:36 PM

You say that the A/C is A OK, on car #1.

So we will have to assume that there are no problems with the control panel, or the A/C relay.

If both fans cycle on and off as needed for engine cooling, then we have to assume the main fan and sub fan relays and fuses are good.

To tell you the truth this is a fairly complicated system. I would have to spend quite a bit of time studying a wiring diagram.

According to the FSM, when the A/C relay is activated it is then a function of the ECU to turn the fans on. I don't have a wiring diagram handy today, so I'm not sure were to start testing.

#14 grossgary

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Posted 06 January 2008 - 07:11 AM

WAW - if the relay is stuck would it always be on or only when the A/C is pushed? or would a failed/stuck closed relay cause it to be on all the time?? relays fail often enough that i would check those first if that's a possibility.

is there a reason this is a problem? the fans come on, that's it? sounds relatively benign.

#15 WAWalker

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Posted 06 January 2008 - 02:50 PM

The problem is that on Car #1 the fans are not coming on when they should. They are only coming on when engine temp reaches the point that the fans are needed to drop engine temp.

They are not running when the A/C compressor is running. In the winter, no this is probably never going to be a "problem". Summer, it may very well be a "problem".

As far as I know I haven't checked but I sure can................The A/C compressor runs continuously when in Defrost mode, and the fans will as well.

In A/C mode the compressor runs as needed to maintain an output temp at the evaporator of ~32-38 deg. F. The fans will cycle on and off with the compressor.

If this is not happening then the system is not working as designed. Weather it is a "problem" is personal opinion and/or weather the car is going to over heat in the summer with the A/C going.




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