94 ATX blows fuse 17

[Robert Duncan]

This is one of the strangest things I have ever seen.

Fuse #17 (supplies the EATC, blend door and blower control) blows when the car is put in drive and the accelerator is touched. If the EATC is OFF it doesn't happen. After the fuse blows the fan will work in manual setting mode but not automatic, there is also no blend door when blown.

Every thing works fine in Park, Neutral and Reverse. Even with the engine reved. Fan auto cycles and blend door functions.

When put in Drive and the engine reved at all, the fan surges then the fuse blows. The brake can be held on (so car is not moving) and it still happens.

I have gone through over 15 fuses running through all these different scenarios.

Does anyone have an idea of where to look?

 

[SlowHeavyObject]

i haven't blown a fuse but my car was having issues with the eatc and throttle too. check your ccrm or the connections to and from. the ccrm is set to tell the eatc to change the a/c clutch, blend door, and blower control based upon signals it senses from the tps, engine rpms, or coolant temperature. whenever you step vigourously on the gas pedal it tells the eatc to change it's output so there must be a short or something wrong with the electrical connections to and from the eatc or it may be the ccrm itself - which was my case.

 

[projectSHO89]

Unfortunately, there is no communication into EATC from any other system in the vehicle. The EATC system is completely independent of the other systems except for demanding A/C clutch engagement by feeding the ACCS signal to the A/C cycling switch.

Rpbert,

Sorry, but I don't see any logical reason for your symptom except possibly an intermittent short circuit that is being caused when the drivetrain moves and a harness is flexed or stressed. I would look in the neighborhood of the cycling and refrigerant containment switches under the hood.

Try unplugging the cycling switch then retesting. Same for the containment switch.

I do not know if this circuit is fed fromthe F17 source, but it is a strong possibility.

Steve

 

[SlowHeavyObject]

sorry, i meant check the connections around the ccrm. it's true that there isn't a direct connection between the ccrm and the eatc, BUT the ccrm DOES control the a/c clutch. when it turns the a/c clutch off when you open the throttle (should only be during wot under normal operation, when something's wrong it acts goofy), the eatc detects that and changes the output of the airflow depending on whether the clutch is on or off.

that might not say much about a blowing fuse but sometimes even the silliest thing like a wire disconnected or shorted from the ccrm will cause a chain-reaction of things that causes the eatc to blow one. like how the dimmer is wired into the radio lights and when something's wrong with that it might not blow the dimmer fuse but the radio fuse instead.

i don't think it could be an intermittent short because you say that you can hold on the brake and not move the car and it still happens - something shouldn't be able to move unless your car shakes/moves/vibrates when this happens.

the reason why i say check those connections is because the only way the throttle is related to the climate control system is through the ccrm. sorry for the confusion.

 

[Robert Duncan]

UPDATE: I disconnected the A/C clutch at the clutch; didn't help. I disconnected the A/C cycling switch; now it does not blow fuses and I have control of the heat (which is what I need for now).

I suspect the CCRM is bad. Since with the clutch disconnected it still blew fuse 17. It is still not clear to me how fuse 17, which is the supply for the blend door and the blower control, is affected by the CCRM. The CCRM seems to have it's own supply.

 

[SHOZ123]

Sounds to me like a bad A/C cycling switch or the wiring between it and the A/C clutch.

No ohm meter eh?

 

[projectSHO89]

slow..

Sorry, but you've got a substantially wrong impression on how the system works...... I don't have time to itemize.

Robert,

Now that you know where (in general) the fault is, time to further isolate it. Based on your results, it appears that F17 does supply the circuit to the cycling and containment switches and tells the CCRM to turn on the clutch. I'd assign a low liklihood to the idea that the CCRM is the fault.

Reconnect the cycling switch and disconnect the containment (high pressure cutout) switch. It's located on the muffler off the compressor just below the oil filter (towards the passenger side a couple of issues). Retest. If the fuse still blows, then either the cycling switch is shorting to ground internally (I'd consider this to be quite unlikely) or there is an intermittent short to ground in the wiring between the cycling switch and the containment switch.

If there is no fault in this segment, install a jumper between the pins at the switch connector for the R/Y & PK/LB wires and retest. If this test blows the fuse, then the short is either in the last wiring segment, the CCRM, or the PCM. The PK/LB wire goes both to the CCRM (pin 21) and the PCM (pin 10) via splice S147.

My suspicion remains with a wiring harness fault since the fault only occurs when the drivetrain flexes. While you're at it, check your motor and transmission mounts for excessive movement and your subframe bushings for play, either of which will exacerbate harness issues.

If you do have a meter, it would likely be possible, with the help of a trusted assistant, to locate a short to ground by isolating each segment with F17 removed.

Good luck. Intermittent faults are about the most frustrating type of fault to locate. You are somewhat lucky (relatively) in that you can reliably recreate the fault.

Steve

 

[SlowHeavyObject]

my bad. my guess was the ccrm because that's what it definitely was in mine, even when the car wasn't moving, although i didn't blow a fuse. i suspected the ccrm because it is one of the more common parts known notoriously for failing on the sho. also i know that many think that fuses only protect wires, when they actually protect circuits and all their components. and we all know that more things are tied to a fuse by relation to the circuit the fuse protects, not direct connection (as evidenced by ford's description of fuse 17 only protecting the eatc, blend door, and blower control yet doesn't mention the a/c cycling switch). so if a component is the cause of a faulty circuit, either the component fails, or a fuse blows, or both. according to ford, you would only expect it was one of those 3 listed items, or the wires in between, that blows fuse 17.

another reason i suspect the ccrm is because of the logic of the circuit. "roughly", when the throttle is pressed, the tps sends a signal to the pcm. the pcm then sends a signal to the ccrm. the ccrm then uses that to determine whether the a/c clutch should be on or off. unless the eatc blend door selection is overridden, the auto function determines the position of the blend door - and when the a/c clutch is off, it is output to the flr-def position. it is wrong to say that the eatc is a self contained system since it is obvious that it needs to read signals from other components (otherwise how would it tell what position the blend door is in? or even what temperature it is in the car?). now since fuse 17 protects the blend door, that would be the first thing to suspect - however, according to the post the blend door still functions without blowing the fuse. the next logical thing to check would be the clutch/ccrm area. heck, maybe even the tps is faulty and sensing wot all the time.

it shouldn't be confusing that the ccrm fuse didn't blow. fuses are placed in a circuit 'before' the component they are protecting (cars use dc current in every circuit except the connection between the battery and alternator). so the ccrm fuse should only blow if there is something wrong with the power supply before it reaches the ccrm. so if the ccrm is failing, the symptoms would not be a blown ccrm fuse right away. according to that logic, you really should start suspecting either the blend door or the wires that connect it first. but like before, the blend door functions fine and doesn't blow the fuse. maybe it's just that simple tho - try pressing all of the output buttons along the bottom of your eatc to switch the door positions and see if the fuse blows.

sorry if i was confusing, but the ccrm was my first guess because that is the only component "electronically" related to the throttle-climate control, and it's the easiest to check/suspect since it is known to fail easily like the tps and cps. the a/c cycling switch is related to many more things and therefore harder to diagnose.

 

[SlowHeavyObject]

This is one of the strangest things I have ever seen.

Fuse #17 (supplies the EATC, blend door and blower control) blows when the car is put in drive and the accelerator is touched. If the EATC is OFF it doesn't happen. After the fuse blows the fan will work in manual setting mode but not automatic, there is also no blend door when blown.

Every thing works fine in Park, Neutral and Reverse. Even with the engine reved. Fan auto cycles and blend door functions.

When put in Drive and the engine reved at all, the fan surges then the fuse blows. The brake can be held on (so car is not moving) and it still happens.

I have gone through over 15 fuses running through all these different scenarios.

Does anyone have an idea of where to look?

The drivetrain still flexes even in reverse, but the fuse doesn't blow unless in drive. that would contradict a harness stress/movement issue. the ccrm only overrides the output in the eatc's "automatic" mode. you can still change the output via the manual buttons, and the a/c clutch would be on/off depending on what button was pressed (under normal conditions). the fan control is also affected along with the blend door by the "automatic" control when the ccrm disables the clutch. the bold points are the reasons why i'm saying the ccrm is being goofy instead of the a/c cycling switch.

 

[projectSHO89]

slow,

Sorry, guy, but you still don't understand..... I don't mean to hurt your feelings, but....

the ccrm then uses that to determine whether the a/c clutch should be on or off.

No. The PCM can send a WOT A/C signal to the CCRM to disable the clutch circuit. The CCRM has no decision making capability, it is simply a dumb switch/relay box that can only turn relays on or off based on the inputs. This signal (WAc) is generated by the PCM only in response to the TPS signal going to WOT.

it is wrong to say that the eatc is a self contained system ...

The electronic portion of EATC system consists of the head unit, several dedicated sensors, the BSC, the BDA, and the A/C clutch control input to the CCRM.... It has no other electronic inputs or outputs.

the a/c cycling switch is related to many more things and therefore harder to diagnose.

On the contrary, it is related to only one thing and is incredibly easy to diagnose. It monitors refrigerant pressure and opens at 22-24 psi decending and closes at 43-45 psi ascending. Can't get much simpler than that unless it is intermittently shorting internally to ground, which I'd suppose is a pretty remote likelihood.

The drivetrain still flexes even in reverse, but the fuse doesn't blow unless in drive. that would contradict a harness stress/movement issue

The DIRECTION of the flex is opposite in FWD or REV. Think about it.

the ccrm only overrides the output in the eatc's "automatic" mode.

The CCRM does not have the capability to override anything. It's just a dumb switch relay box. It requires the AC demand signal to be preset and the WOT status to be absent to energize the A/C clutch relay.

<End of Lecture>


Robert,

The Refrigerant Containment Switch, in addition to passing the AC demand signal from the cycling switch to the CCRM via a pair of normally closed contacts, has a secondary function of engaging the high speed cooling fan circuit by grounding the HFC input to the CCRM. I'd suggest inspecting this portion of the circuit very carefully for visible wiring defects or connector contamination

Steve

 

[SlowHeavyObject]

no feelings hurt. didn't mean to be argumentative. sometimes problems aren't that incredibly technical. i know that's not exactly how the system works, but "roughly" in laymans terms. it is sometimes hard to follow technical instructions. like every problem, the first response is always the most obvious, and in my opinion it's still the ccrm. i figured i'd offer my opinion because my car was a 94 atx also and had nearly the same exact problem, sans fuse. i'm going with the gut on this one (the same that tells me when my car runs rough, all it may need is just a tune-up, not an overhaul). i just think having to go through all those tests is a little bit of overkill, especially after someone goes through 15 fuses trying to isolate the problem, and when the ccrm is a universally well known culprit for failing. i did say to check the ccrm and it's connections aournd the area, which includes all off the circuits that have been mentioned in the other posts. sometimes things are weird - like how should a shorted wire under the dash be able to fry an alternator? (which also happened on my car although it defies all regular diagnostic thinking). i will admit tho that i may still be wrong about the cause. everyone is entitled to their own opinion. let us know how it turns out.