Why does it run fine until A/C, heat or defogger turned on, then goes dead?

System Description NEEL0216 MODELS WITHOUT POWER DOOR LOCKS NEEL0216S01 The rear window defogger system is controlled by the rear window defogger timer. The rear window defogger operates only for approximately 15 minutes. The rear window defogger switch is integral to the air control. Power is supplied at all times
to rear window defogger relay terminal 5
through 20A fuse [No. 25, located in the fuse block (J/B)]. With the ignition switch in the ON or START position, power is supplied
through 10A fuse [No. 5, located in the fuse block (J/B)]
to rear window defogger relay terminal 1, and
to rear window defogger timer terminal 1. Ground is supplied to air control (rear window defogger switch) terminal 8 and rear window defogger timer terminal 4 through body grounds M14 and M68. With the rear window defogger switch (located in air control) ON, ground is supplied
to rear window defogger timer terminal 3
through air control (rear window defogger switch) terminal 8. Rear window defogger timer terminal 2 then supplies ground to the rear window defogger relay terminal 2. With power and ground supplied, the rear window defogger relay is energized. Power is supplied
through terminal 3 of the rear window defogger relay
to rear window defogger terminal +. Rear window defogger terminal - is grounded through body ground R102. With power and ground supplied, the rear window defogger filaments heat and defog the rear window. When the system is activated, the rear window defogger indicator illuminates in the air control. Power is supplied
from rear window defogger relay terminal 3
to air control (rear window defogger switch) terminal 4. Air control terminal 8 is grounded through body grounds M14 and M68. MODELS WITH POWER DOOR LOCKS NEEL0216S02 The rear window defogger system is controlled by the smart entrance control unit. The rear window defogger operates only for approximately 15 minutes. The rear window defogger switch is integral to the air control. Power is supplied at all times
to rear window defogger relay terminal 5
through 20A fuse [No. 25, located in the fuse block (J/B)] and
to smart entrance control unit terminal 49
through 7.5A fuse [No. 28, located in the fuse block (J/B)]. With the ignition switch in the ON or START position, power is supplied
through 10A fuse [No. 5, located in the fuse block (J/B)]
to rear window defogger relay terminal 1 and
to smart entrance control unit terminal 27. Ground is supplied to air control (rear window defogger switch) terminal 8 and smart entrance control unit terminals 43 and 64 through body grounds M14 and M68. With the rear window defogger switch (located in air control) ON, ground is supplied
to smart entrance control unit terminal 14
through air control (rear window defogger switch) terminal 1. Smart entrance control unit terminal 37 then supplies ground to the rear window defogger relay terminal 2. With power and ground supplied, the rear window defogger relay is energized. Power is supplied
through terminal 3 of the rear window defogger relay
to rear window defogger terminal +.
Rear window defogger terminal - is grounded through body ground R102. With power and ground supplied, the rear window defogger filaments heat and defog the rear window. When the system is activated, the rear window defogger indicator illuminates in the air control. Power is supplied
from rear window defogger relay terminal 3
to air control (rear window defogger switch) terminal 4. Air control (rear window defogger switch) terminal 8 is grounded through body grounds M14 and M68

replace switches

front or rear.?
my guess, wild is, the rear electric defogger, is dead.
the test is so easy.
attach any voltmeter to the 2 grid terminal. and turn the defroster on.
12v there? yes, then the grid is open.
no> the relay that feeds it is bad. (or its controls or FUSE is blown)
check all fuse first.

HEATING AND AIR CONDITIONING
HONDA CIVIC 2001 - 2005

How to retrieve DTC:

The heater control panel has self-diagnosis function. To run the self-diagnosis function, do the following:

1.Turn the blower fan OFF.
2.Press and hold the recirculation control switch and the rear window defogger switch down.
3.Turn the ignition switch ON (ll).
4.Release both switches. The recirculation indicator and the rear window defogger indicators come on. The recirculation indicator goes off 3 seconds later and the A/C indicator comes on, then the self-diagnosis will begin. About 10 seconds later, the self-diagnosis will finish and the A/C indicator goes off.

If any trouble is found, the recirculation indicator blinks the diagnostic trouble code (DTC) to indicate a faulty circuit or component.
If the system is ok, the recirculation indicator stays off.

HEATING AND AIR CONDITIONING
HONDA CIVIC 2001 - 2005
How to retrieve DTC:
The heater control panel has self-diagnosis function. To run the self-diagnosis function, do the following:
1.Turn the blower fan OFF.
2.Press and hold the recirculation control switch and the rear window defogger switch down.
3.Turn the ignition switch ON (ll).
4.Release both switches. The recirculation indicator and the rear window defogger indicators come on. The recirculation indicator goes off 3 seconds later and the A/C indicator comes on, then the self-diagnosis will begin. About 10 seconds later, the self-diagnosis will finish and the A/C indicator goes off.
- If any trouble is found, the recirculation indicator blinks the diagnostic trouble code (DTC) to indicate a faulty circuit or component.
- If the system is ok, the recirculation indicator stays off.

DTC TROUBLESHOOTING INDEX
DTC (Recirculation indication blinks) Detection Item Page
7An open in the air mix control motor circuit.21 - 16
8A short in the air mix control motor circuit.21 - 16
9A problem in the air mix control linkage, door, or motor.21 - 17
10An open or short in the mode control motor circuit.21 - 18
11A problem in the mode control linkage, doors, or motor.21 -19
12A problem in the blower motor circuit.21 - 20
13A problem in the EEPROM in the heater control panel;
(THE CONTROL PANEL MUST BE REPLACED).21 - 38
14An open in the evaporator temperature sensor circuit.21 - 23
15A short in the evaporator temperature sensor circuit.21 - 24
- In case of multiple problems, the recirculation indicator will indicate only the DTC with the least number of blinks.
- In case of an intermittent failure, the heater control panel will store the DTC until the ignition is turned off.

Control head is failing

Rear Defogger Inoperative, But Heated Mirrors Operate Correctly
1. Connect scan tool. Turn ignition switch to RUN position. Turn rear defogger on. Using scan tool, display BCM
outputs. If rear defogger is being requested on, go to next step. If rear defogger is not being requested on, go to
step 10).
2. Ensure ignition switch is in RUN position. Remove rear defogger relay from rear junction block, located on center
right rear of passenger compartment, under rear seat. Connect test light between ground and defogger relay
harness connector terminal F3 (Brown wire). If test light illuminates, go to next step. If test light does not
illuminate, go to step 11).
3. Connect test light between ground and defogger relay harness connector terminal A2 (Red wire). If test light
illuminates, go to next step. If test light does not illuminate, go to step 12).
4. Connect test light between defogger relay harness connector terminals A2 (Red wire) and B3 (Purple wire). If test
light illuminates, go to step 13). If light does not illuminate, go to next step.
5. Disconnect rear defogger positive and negative feed bus connectors. Connect a jumper wire between defogger
relay harness connector terminals F3 (Brown wire) and A4 (White wire). Connect test light between ground and
positive feed bus connector terminal "A" (Black wire). If test light illuminates, go to next step. If test light does not
illuminate, go to step 8).
6. Connect test light between positive feed bus connector terminal "A" (Black wire) and negative feed bus connector
terminal "B" (Black wire). If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
7. Repair open in Black wire between rear defogger and ground. Recheck system operation.
8. Repair open in Purple wire between rear junction block and heated backlight antenna module. Recheck system
operation.
9. Check for proper terminal contact at rear defogger connectors. Repair as necessary. Recheck system operation.
10. Check for proper terminal contact at BCM. If terminal contact is okay, replace BCM. Recheck system operation.
11. Repair open in Brown wire between rear junction block and instrument panel junction block. Recheck system
operation.
12. Repair open in Red wire between rear junction block and underhood junction block (located in right front corner of
engine compartment, between battery and strut tower). Recheck system operation.
13. Connect test light between defogger relay harness connector terminals F3 (Brown wire) and A4 (White wire). If
test light illuminates, go to next step. If test light does not illuminate, go to step 16).
14. Reinstall defogger relay. Disconnect BCM 32-pin Pink connector C2. BCM is located behind right side of instrument
panel, near rear of glove box. Using DVOM, check voltage between ground and BCM harness connector C2
terminal A3 (White wire). If any voltage is present, go to next step. If no voltage is present, go to step 17).
15. Repair open or short to ground in White wire between rear junction block and BCM. Recheck system operation.
16. Check for poor connection at defogger relay terminals. If connections are okay, replace defogger relay. Recheck
system operation.
17. Check for proper terminal contact at BCM. If terminal contact is okay, replace BCM. Recheck system operation.

The rear defogger is controlled by the Electronic Time and Alarm Control Module (ETACM). It receives a signal from the switch, and if the car is running, turns on the rear window defogger. Most frequently the problem is a blown 30A defogger fuse. Other common problems are the defogger switch itself or the switch not being plugged in properly, but there can also be a bad defogger relay, defective ETACM, or wiring issue. If you're capable of doing some electrical diagnosis, I'd encourage you to register for a free account at www.hmaservice.com (requires Internet Explorer and Adobe SVG Viewer) and print the schematic from the site. Also, does the indicator lamp come on when you depress the defogger button,I hope this help you in the right direction now you know how it works

My volvo 940gl did exactly the same, it turned out to be the fuel injection relay. I changed it and the car ran perfectly happy for the next 2 years until I sold it.

I am assuming your talking about your ac. if so you can run a self diagnostic check, if you have manual temp control the led on the rear defogger can blink codes. turn car on, turn blower knob on(anyspeed), temp full cool, zone to defrost. press defogger button for 5 secs until it blinks. if it goes out 1st test is ok, rotate zone control and each section will be tested, the light will blink for each zone and then go out if it is ok, if it stays on this may be where your problem is.