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Should the fan kick on with defrost? by Gokart
Started on: 09-05-2013 08:00 AM
Replies: 15 (552 views)
Last post by: Marvin McInnis on 09-07-2013 09:17 AM
Gokart
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Report this Post09-05-2013 08:00 AM Click Here to See the Profile for GokartSend a Private Message to GokartEdit/Delete MessageReply w/QuoteDirect Link to This Post
Temp light came on this morning on my way to work. I tested my fan by turning on the AC and it came on but doesn't when the defrost button is depressed and I thought it should? Maybe a dying relay? Any input greatly appreciated
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Old Lar
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Report this Post09-05-2013 09:01 AM Click Here to See the Profile for Old LarSend a Private Message to Old LarEdit/Delete MessageReply w/QuoteDirect Link to This Post
When defrost is on, it should turn on AC and radiator fan should kick on.
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Gokart
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Report this Post09-05-2013 10:05 AM Click Here to See the Profile for GokartSend a Private Message to GokartEdit/Delete MessageReply w/QuoteDirect Link to This Post
That's what I thought. Thanks for confirming.
I'll assume its the relay and I'll start with replacing that when I get home this afternoon.
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Carrolles
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Report this Post09-05-2013 04:38 PM Click Here to See the Profile for CarrollesClick Here to Email CarrollesSend a Private Message to CarrollesEdit/Delete MessageReply w/QuoteDirect Link to This Post
My understanding is that the fan turns on when the A/C is in MAX, Normal, or bilevel, not in Defrost.
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EvilSqueezles
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Report this Post09-05-2013 04:45 PM Click Here to See the Profile for EvilSqueezlesClick Here to Email EvilSqueezlesSend a Private Message to EvilSqueezlesEdit/Delete MessageReply w/QuoteDirect Link to This Post
I don't understand why defrost (a heat function) would turn on the A/C.
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MeadmakerDave
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Report this Post09-05-2013 04:50 PM Click Here to See the Profile for MeadmakerDaveClick Here to Email MeadmakerDaveSend a Private Message to MeadmakerDaveEdit/Delete MessageReply w/QuoteDirect Link to This Post
I'm looking at a wiring schematic for the 1984 with AC.

It appears by the schematic that the coolant fan relay should be energized in the Max, Norm, and BL positions, but not in the Defrost position - even though the AC power relay is also energized in Defrost.

That's my read on the diagram anyway.

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MeadmakerDave
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Report this Post09-05-2013 04:52 PM Click Here to See the Profile for MeadmakerDaveClick Here to Email MeadmakerDaveSend a Private Message to MeadmakerDaveEdit/Delete MessageReply w/QuoteDirect Link to This Post

MeadmakerDave

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quote
Originally posted by EvilSqueezles:

I don't understand why defrost (a heat function) would turn on the A/C.


The AC runs to dry the air in the cabin so that the windows will defrost more quickly.
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Gokart
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Report this Post09-05-2013 05:02 PM Click Here to See the Profile for GokartSend a Private Message to GokartEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by MeadmakerDave:


The AC runs to dry the air in the cabin so that the windows will defrost more quickly.


So does the fan turn on with the defrost setting?

Edit to add I'm trying to narrow down my overheating issue this morning. I had to keep the AC on while driving back home.
If the fan does turn on when the AC is on does this tell me the relay is good? I called TFS store this morning and they believe I need a new fan switch.

[This message has been edited by Gokart (edited 09-05-2013).]

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85 SE VIN 9
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Report this Post09-05-2013 07:21 PM Click Here to See the Profile for 85 SE VIN 9Click Here to Email 85 SE VIN 9Send a Private Message to 85 SE VIN 9Edit/Delete MessageReply w/QuoteDirect Link to This Post
My A/C belt came off on pretty much the first hot day of the year lol, but until then, yes the A/C and fan ran whenever the system was in anything but "vent" or "off." I put it in these positions to avoid the belt squeal and loss of power, but in traffic the engine temp would come up so I would put it one of the others to bring it down. It sounds like the problem is in the controls.
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MeadmakerDave
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Report this Post09-05-2013 09:49 PM Click Here to See the Profile for MeadmakerDaveClick Here to Email MeadmakerDaveSend a Private Message to MeadmakerDaveEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Gokart:


So does the fan turn on with the defrost setting?

Edit to add I'm trying to narrow down my overheating issue this morning. I had to keep the AC on while driving back home.
If the fan does turn on when the AC is on does this tell me the relay is good? I called TFS store this morning and they believe I need a new fan switch.



By what I'm reading on the schematics for the 84 2.5L with AC it should not come on with defrost. I can try to post a link to the schematics I'm using.
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TONY_C
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Report this Post09-06-2013 07:57 AM Click Here to See the Profile for TONY_CSend a Private Message to TONY_CEdit/Delete MessageReply w/QuoteDirect Link to This Post
For the 84, the fan does not run in Defrost mode unless the coolant temperature goes high enough to kick the fan on thru the fan temp switch. I think the thought from the engineers was that it would be cooler outside when the defrost mode was needed and there would not be a need to run the fan to cool down the condenser.
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PFF
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85 SE VIN 9
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Report this Post09-06-2013 06:49 PM Click Here to See the Profile for 85 SE VIN 9Click Here to Email 85 SE VIN 9Send a Private Message to 85 SE VIN 9Edit/Delete MessageReply w/QuoteDirect Link to This Post
It apparently doesn't run in defrost. I pulled into the garage, set the controls to defrost and turned off the engine with the door open. That's when the fan can be heard winding down. No fan in defrost, 85 GT.
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Gokart
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Report this Post09-06-2013 08:32 PM Click Here to See the Profile for GokartSend a Private Message to GokartEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 85 SE VIN 9:

It apparently doesn't run in defrost. I pulled into the garage, set the controls to defrost and turned off the engine with the door open. That's when the fan can be heard winding down. No fan in defrost, 85 GT.


Thanks for investigating and reporting your findings. I haven't overheated since I stsrted this topic and did not run the a/c today. Maybe a bad reading somehow and a one time incident? I'll swap out the new fan switch just the same though when it arrives from TFS.
Thanks for all the replies.
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Marvin McInnis
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Report this Post09-07-2013 01:52 AM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by TONY_C:

For the 84, the fan does not run in Defrost mode ...



That is correct for all Fiero years and models using the DA6/HR6 compressor. I can't confirm it for systems using the V5 compressor.

 
quote

... unless the coolant temperature goes high enough to kick the fan on thru the fan temp switch.



... or unless the high-pressure fan switch on the back of the A/C compressor closes. That will also turn on the radiator fan.


 
quote

I think the thought from the engineers was that it would be cooler outside when the defrost mode was needed and there would not be a need to run the fan to cool down the condenser.



Correct. And the A/C compressor clutch will not even engage at low air temperatures (below ~40 F), due to the pressure-cycling switch on the accumulator never closing.

(I also appreciate your explaining why it's designed that way.)

[This message has been edited by Marvin McInnis (edited 09-07-2013).]

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black88fiero
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Report this Post09-07-2013 03:45 AM Click Here to See the Profile for black88fieroClick Here to Email black88fieroSend a Private Message to black88fieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
In my 88 4 cyl car the fan comes on with the defrost button pushed.. One day it did not, i pulled the heater control out, the copper strip on the circuit board actually had a burnt/missing spot in it.. Jumped the gap with the button depressed and it came on..
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Marvin McInnis
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Report this Post09-07-2013 09:17 AM Click Here to See the Profile for Marvin McInnisClick Here to visit Marvin McInnis's HomePageSend a Private Message to Marvin McInnisEdit/Delete MessageReply w/QuoteDirect Link to This Post
Don't take my word for it. Here is page 8A-31-0 from the '88 Fiero FSM (GM/Helm):

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