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88 GT Heater Fuse Blown by Pyrostatic
Started on: 09-26-2021 04:42 PM
Replies: 29 (266 views)
Last post by: buddycraigg on 10-08-2021 08:29 PM
Pyrostatic
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Report this Post09-26-2021 04:42 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hello,

Sometime over the weekend the 25amp fuse for my heater and A/C blew (fuse 8). I replaced the fuse and the heater ran for a second on the new fuse, but when I clicked over to defrost, the fuse blew again. The heater and defrost worked perfectly fine until this weekend.

Can anyone offer any suggestions?
I searched the forum and was unable to find any posts with this particular problem. If I have missed something, a link would be kindly appreciated.

Thank-you.
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Report this Post09-26-2021 05:48 PM Click Here to See the Profile for IMSA GTClick Here to Email IMSA GTSend a Private Message to IMSA GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
If the blower runs fine with the heater off and it also blows cold air when the AC is on, it may be an issue with the heater resistor. It is in the front trunk along the firewall and is indicated by the purple arrow in the picture.

[This message has been edited by IMSA GT (edited 09-26-2021).]

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Gall757
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Report this Post09-26-2021 06:14 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
It would be a good time to check for a mouse nest. The heater resistor can be trouble.
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Report this Post09-26-2021 06:51 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
What is the fuse labeled?
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Report this Post09-26-2021 06:55 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post

buddycraigg

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quote
Originally posted by IMSA GT:

If the blower runs fine with the heater off and it also blows cold air when the AC is on, it may be an issue with the heater resistor. It is in the front trunk along the firewall and is indicated by the purple arrow in the picture.




The resistor only play a part on fan speeds 1,2,3. The resister is bypassed when you have the fan on the high setting.

and funny. I think that is one of my pictures. I'm glad I'm helping out, even if I'm not around.
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Report this Post09-26-2021 07:12 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by buddycraigg:

What is the fuse labeled?


25 amp white.. HEAT/AC
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Report this Post09-26-2021 07:15 PM Click Here to See the Profile for IMSA GTClick Here to Email IMSA GTSend a Private Message to IMSA GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by buddycraigg:


The resistor only play a part on fan speeds 1,2,3. The resister is bypassed when you have the fan on the high setting.

and funny. I think that is one of my pictures. I'm glad I'm helping out, even if I'm not around.


I had to "borrow" it
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Report this Post09-26-2021 10:27 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by IMSA GT:


I had to "borrow" it


I feel good that I even recognized it.
Please "borrow" all that you can to help everyone you can.
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Report this Post09-26-2021 10:31 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post

buddycraigg

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quote
Originally posted by Gall757:


25 amp white.. HEAT/AC


Can someone show me that schematic?
I don't have access to that readily available to those anymore.
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Report this Post09-27-2021 03:27 AM Click Here to See the Profile for RexgirlSend a Private Message to RexgirlEdit/Delete MessageReply w/QuoteDirect Link to This Post
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Report this Post09-27-2021 01:05 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post



Thanks for the feedback, the heater resistor seems to look good to me.

Any other ideas?
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Report this Post09-28-2021 03:52 PM Click Here to See the Profile for RexgirlSend a Private Message to RexgirlEdit/Delete MessageReply w/QuoteDirect Link to This Post
Possibly a shorted Mode Door Actuator (motor) ?
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Report this Post09-28-2021 08:00 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rexgirl:

Possibly a shorted Mode Door Actuator (motor) ?


Yikes, 25 amps through one of those motors is a lot.

Rexgirl
Thanks for posting the schematic. ( gave you a +)

Pyrostatic
I do not remember a relay called "AC power relay"
Look at the picture that IMSA GT posted.
The relay with the yellow arrow going to it.
Does it have brown, brown, pink, black wires going to it?
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Report this Post09-29-2021 10:03 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Full drawing showing cutoff right side...

Power Relay is why Blower Only shut off when Control Head is Off along w/ rest of AC.

May need this too for V6 but skipping engine blower because 88 deleted that.
CLICK FOR FULL SIZE


Likely motor have problem even if can run @ high speed.
Can be motor dying to wires and other parts cause low volts.

Motor w/ bad wiring gets low volts and can pop a fuse when you're lucky. See my Cave, Electric Motors
Motor dying can cause high draw @ low speeds and pop a fuse.
Blower at High speed bypass low speed parts and doesn't have a fuse. Dying motor still draws more power and a problem to rest of car.

If car has Low Volts problems then likely other things have problems too. Example: Rad Fan is basically heater blower on High and doesn't have a fuse for the motor. Do Not Trust Volt meter in the dash.

Get a "small" meter w/ DC Amp Clamp.
If you have whatever blowing fuses or Battery Leaches this will find them w/o cutting wires etc.
Example: https://www.amazon.com/Uni-...itance/dp/B00O1Q2HOQ

If not a relay, motor, or other things w/ plugs... Might what a fuse blinker. aka a "short tester automotive"
example: https://www.amazon.com/Tool...Tester/dp/B000RFLR0U
Red part is blinker can that load up a short w/o burning fuses etc. Can get all electronic ones too.
take a blow fuse and cut plastic some to use it to connect the blinker parallel to the dead fuse

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(Jurassic Park)


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Report this Post09-29-2021 03:41 PM Click Here to See the Profile for RexgirlSend a Private Message to RexgirlEdit/Delete MessageReply w/QuoteDirect Link to This Post
It appears this fuse also feeds the air distribution motors, and one motor may be shorted to ground.
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Report this Post09-29-2021 06:48 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rexgirl:
It appears this fuse also feeds the air distribution motors, and one motor may be shorted to ground.
CLICK FOR FULL SIZE
Maybe but unlikely...
RT1 (Shown below in Red Box.) and RT2 are PTC Thermistors that limit power to the Mode Motors. In very short... They can, likely will, cook off if there's a short downstream of them and prevent blowing a fuse repeatedly.
On the Control Head, they are small disk shape parts similar to ceramic capacitors but different color.
Also those motors and built in switches are very small and fry easy too. If RT1 or RT2 fails shorted, the motor block will die and very fast because can't handle full power.

[This message has been edited by theogre (edited 09-29-2021).]

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Report this Post09-29-2021 07:27 PM Click Here to See the Profile for RexgirlSend a Private Message to RexgirlEdit/Delete MessageReply w/QuoteDirect Link to This Post
Yes, unlikely. What do you suggest he do next Mr. Dave? I was thinking the OP might want to see if the blower runs on High as Buddy suggested, to check for its proper operation.
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Report this Post09-29-2021 07:41 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
I want to see if the fuse still blows with the AC power relay is disconnected.
I want to rule out a short in the AC compressor control circuit.

I don't think it is a problem with the blower motor, cause the fusable link would have blown.
You can disconnect the purple wire going to the blower as a test if you want.
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Pyrostatic
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Report this Post09-30-2021 03:57 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thank-you so much for looking into this guys. I really appreciate it.

I have a question:
In this picture:


Is the relay I circled the one that is located in the back hatch beside the fuel pressure relay? Or are they two different relays?

The reason I ask is, I had an exhaust leak in the Y of the exhaust. It ended up melting a bunch of wires, especially the ones going to the "A/C Compressor Control Relay" and the "Fuel Pump Relay". I couldn't get the fuel pump relay to work right with the stock wiring after that, and ended up running a power line from the junction block to the fuel pressure relay with an inline fuse. I never hooked that A/C relay beside it back up as the A/C didn't work anyways. I didn't realize it could be important for running the heat, defrost, blower etc. (The heater and defrost did work for a while without the "A/C Compressor Control Relay" being hooked up.)

So... ya, is that relay circled in the picture the one beside the fuel pressure relay?
If so, is there an easier way to fix my problem without completely restoring the A/C relay?
Thank-you.
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Report this Post09-30-2021 07:15 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Both relays above are in the front...
Notice some connection go thru C100 below next to Brake Booster.

Power Relay runs most of the system via pnk then blk/wht wires.
If wires fried in back... then yes, likely still have problems there blowing fuses.

"best" is pull off ac/radio trim to access the control head to pull the plug on blower speed switch.
Just pull that plug and still popping fuse then ISN'T a blower problem.
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Report this Post10-01-2021 03:12 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post
Ok, finally got some time to look at this sucker.

 
quote
Originally posted by theogre:
"best" is pull off ac/radio trim to access the control head to pull the plug on blower speed switch.
Just pull that plug and still popping fuse then ISN'T a blower problem.


I disconnected the blower speed switch. I put the car in accessory position with a new fuse, and the heater controls off. Again, when I clicked the heater on, the fuse instantly went.
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Report this Post10-01-2021 03:25 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by buddycraigg:
Pyrostatic
I do not remember a relay called "AC power relay"
Look at the picture that IMSA GT posted.
The relay with the yellow arrow going to it.
Does it have brown, brown, pink, black wires going to it?


It looks like 3 brown and 1 pink, but one could be black.

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Report this Post10-01-2021 03:35 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by buddycraigg:

I want to see if the fuse still blows with the AC power relay is disconnected.
I want to rule out a short in the AC compressor control circuit.

I don't think it is a problem with the blower motor, cause the fusable link would have blown.
You can disconnect the purple wire going to the blower as a test if you want.


I tried a new fuse with the AC power relay disconnected (the yellow marked relay in the picture). The fuse did not blow, I could toggle between vent, heater and defrost and hear the changes whirring.
Of course no air comes through...

Thanks Buddy, I wish I was smart enough to know what to do next.
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Report this Post10-01-2021 08:01 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Pyrostatic:
The reason I ask is, I had an exhaust leak in the Y of the exhaust. It ended up melting a bunch of wires, especially the ones going to the "A/C Compressor Control Relay"

I believe you should look into those wires.

[This message has been edited by buddycraigg (edited 10-01-2021).]

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Report this Post10-01-2021 09:31 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
"other part" of blk/wht just goes thru console to AC clutch relay in rear of car...
C203 is in console rear w/ other some engine wires.


leave speed switch pulled
pull clutch relay next.
No blow?
reconnect clutch relay and unplug AC clutch.

Clutch Relay bad and/or wires could still be cooked from exhaust leak at or anywhere behind bulkhead bushing on fire or clutch coil itself is bad and took the relay w/ it.

Clutch Relay contact should open when unplug, AC Off or Key Off but bad clutch coil etc can weld that closed.
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Report this Post10-02-2021 02:23 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by theogre:

leave speed switch pulled
pull clutch relay next.
No blow?
reconnect clutch relay and unplug AC clutch.

Clutch Relay bad and/or wires could still be cooked from exhaust leak at or anywhere behind bulkhead bushing on fire or clutch coil itself is bad and took the relay w/ it.

Clutch Relay contact should open when unplug, AC Off or Key Off but bad clutch coil etc can weld that closed.


Thanks Buddy and Ogre.

I haven't had the "A/C Compressor Control Relay" hooked up in months...
I didn't repair the wires going to it.

Can I just take that black/ white wire and ground it? instead of hooking the relay back up?
I just want heat and defrost.

Thank-you.
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Report this Post10-02-2021 03:46 PM Click Here to See the Profile for RexgirlSend a Private Message to RexgirlEdit/Delete MessageReply w/QuoteDirect Link to This Post
Do NOT ground the black/white wire.
If your "A/C Compressor Control Relay" has not been hooked up, then the short is not in your A"C compressor clutch.
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Report this Post10-03-2021 02:56 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rexgirl:
⚠️ Warning: Do NOT ground the black/white wire.
If your "A/C Compressor Control Relay" has not been hooked up, then the short is not in your A"C compressor clutch.
Warning added...
because Ground that Will Blow a Fuse.

Buy the short finder kit at minimum as posted above should quickly find blk/wht shorted out somewhere.
if not burn in rear, take out console then check there.
May have pinch the hardness or put a screw thru it causing this too.

Don't leave the "blinker" w/ power on while removing whatever to follow the harness. They, blinker and wiring, can get very warm to hot if have power on.

Pop C203 will isolate the short more...

If pulling C203 and still blow fuse...
Last is Could pull C100 but can't use car power to trace a shorted wire same way. Only small section from the fuse is connected now But can test AC power relay wires, brn and pnk, doesn't shorted out w/ test light and +12v.
"Last" because C100 like C500 has a captive bolt to pull the connector apart and very awkward to reach under the dash.
W/ C100 unplugged the relay wires should not light a test lamp connected to +12v or should read OL w/ digital Ω meter connected to ground.

[This message has been edited by theogre (edited 10-03-2021).]

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Report this Post10-03-2021 04:50 PM Click Here to See the Profile for PyrostaticClick Here to Email PyrostaticSend a Private Message to PyrostaticEdit/Delete MessageReply w/QuoteDirect Link to This Post
Hello Again,

You guys got it! That black and white wire was the problem, it was grounding. I fixed that and put the relay back on in the front. Heater and defrost work again now!

Thanks so much for figuring out what the problem was guys!
You guys are awesome!
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Report this Post10-08-2021 08:29 PM Click Here to See the Profile for buddycraiggClick Here to Email buddycraiggSend a Private Message to buddycraiggEdit/Delete MessageReply w/QuoteDirect Link to This Post
I am glad to have been of help. I am sure ogre feels the same.
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