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So my 94 Civic blew the 20A condenser fan fuse in the under-hood fuse box. I replaced it and it blew again about 10 minutes into a drive. I briefly looked at the schematic for this circuit in the Helm manual and see that it powers both the AC condenser fan and the AC compressor clutch. I have had this fuse blow on my EF Civic, and the cause was that "bullet connector" for the wire to the AC compressor had all the rubber crumble off of it, and the wire was shorting out to body. I looked quickly at the wiring for the AC compressor clutch on the EG Civic and don't see any exposed wiring. With the fuse replaced and AC on, both the fan and compressor run for a few minutes until the fuse blows.I also tried unplugging the fan to see if I could isolate the issue to the fan, but the fuse still blew. My question is, is there anything besides a short that may cause this fuse to blow? Specifically - could the compressor going bad, a refrigerant over-charge/under-charge, a system blockage, or something like that cause the fuse to blow? I would think the clutch operates like a solenoid - mechanical load on the compressor wouldn't translate to a higher electrical load...is that correct?
I know enough about auto AC to be dangerous, but I'm by no means an expert on auto AC. Appreciate any constructive input.
I would suspect it is due to a short; but, somewhere else along the circuit. Check the wire harness going to Connector C754, this is the wiring to the A/C compressor thermal protector. The wiring there or somewhere else may have a cut, then with vibration will cause an intermittent short somewhere when the car is running.
To try to rule out the compressor clutch, you can disconnect the compressor clutch connector. Turn on the A/C (of course the A/C won't actually run; but, the compressor clutch relay should be energized to close the relay contact and allow power from Under-hood Fuse No. 35 (20A) to go through the relay to the wiring for the compressor clutch).
The clutch current will not vary from refrigerant pressure or other mechanical factors. It's strictly a matter of voltage and resistance. The clutch coil can develop internal shorts and draw too much current. The resistance of the coil should be higher than 3 ohms. This would correspond to a current of about 4 amps. The current can be measured with a clamp-on amp meter that measures DC.
I did the test that @tech8 suggested and I did not blow the fuse with the compressor disconnected, which showed that it wasn't something with the fan portion of the circuit.
I'm getting 3.4 ohms on the clutch coil, and my meter tells me there is continuity across the coil. This is no doubt where the short is, as I've also pulled the AC subharness and inspected it for any shorts and it all looks good. I've pulled the compressor and pulled the pulley - just need some longer snap ring pliers to be able to get the clutch off. Now, is it worth it to replace just the clutch, or should I just replace the whole compressor? I can get a Four Seasons clutch on Amazon for about $70 or a new Denso brand compressor from Rock Auto for $200. I think I can handle the clutch replacement myself, but is it worth it to put a new (Four Seasons brand) clutch on an OEM Sanden compressor with 183,000 miles? Or, should I just suck it up and buy a whole new compressor?
I buy used ones off of eBay for project cars. Sometimes a junk yard will pull a new looking or remaned one off of a wrecked car that had regular maintenance. I got a virtually brand new one for $60 off eBay with a warranty
if it was me, I would just replace the entire compressor instead of replacing just the clutch. Kind of pointless to replace it and then something internal goes bad shortly after re-install.
Yeah, I talked to a buddy who does AC for a living and he also recommended replacing the entire compressor. I'm going to order the Denso unit, a new dryer, and a new o-ring kit as well. Tony, I can recharge it myself, so just another $10-$15 for some cans of R134a. It shouldn't be a problem.
You've got the diagrams for the 94-95 AC system? Different from the 92 available online, and 93 is different again. If not, I posted them in my build thread. Check my DIYs for link.
Hey, thanks for that. No, I've got the first edition Helm manual printed in September 1991. When I pulled the loom off the subharness and started going through it, I did notice some differences between what I had and what the manual showed.
With 180k+, you shoulda at least flushed it since your compressor didn’t have a catastrophic failure.
We adopted a policy at our garage to replace the condenser during an A/C system replacement due to so many newer vehicles having condensers that can’t be adequately flushed because of how narrow the tubes are IF there is a catastrophic failure; but for compressor clutch failure, we make a judgment call based on what kind of junk we blow out during an attempted flush.
Appreciate the info, I'll be sure to look more closely at the condenser next time. What do you flush with, and I assume you you flush backwards from the receiver side? I've got a friend who has done auto AC for about 30 years and one time he was helping me about 10 years ago and I'm pretty sure I saw him flush with brake parts cleaner followed by compressed air.
Brake cleaner followed by compressed air is fine, but you can get a can of a/c flush from a parts store. Sometimes you have to get creative with hoses and funnels to pour it in the lines effectively, and just follow it thoroughly with compressed air. Back flushing is good to start with, but alternate directions.
Thanks again for the info. Auto AC is one area of knowledge I could stand to learn more about.
You mentioned making the call as to whether or not to replace the condenser based on what kind of stuff comes out. So during the back and forth flush, do you cover the exit with a rag to catch anything that may come out? What kind of bad stuff are you looking for?
What about the evaporator...do you flush it too on an overhaul, or just mainly the condenser?
I'm assuming that by flushing, you're not only pulling out potential contaminants but also oil. Do you just follow the FSM for the amount of oil to put back into the system? I know there is a chart showing how much oil to put in the system for each component that is replaced.
Lastly - oils. R134a needs PAG oil, correct? Is PAG 100 acceptable for EG Civics with R134a systems? How about for EF Civics with R12 systems that have been converted to R134a?
Thanks again for the info. Auto AC is one area of knowledge I could stand to learn more about.
You mentioned making the call as to whether or not to replace the condenser based on what kind of stuff comes out. So during the back and forth flush, do you cover the exit with a rag to catch anything that may come out? What kind of bad stuff are you looking for?
I recommend white paper towels, like Scott rags-in-a-box. You’re looking for glitter and/or metal fragments.
Originally Posted by DaX
What about the evaporator...do you flush it too on an overhaul, or just mainly the condenser?
Yes, flush the evaporator.
DO NOT FLUSH THE COMPRESSOR.
Originally Posted by DaX
I'm assuming that by flushing, you're not only pulling out potential contaminants but also oil. Do you just follow the FSM for the amount of oil to put back into the system? I know there is a chart showing how much oil to put in the system for each component that is replaced.
Go by the FSM. It’s like 6oz or something.
The rule of thumb is “2oz per component” for a decent calculation, but that yields too much sometimes as in this case with a half sized condenser and such a small accumulator. Too much oil in the system can cause cooling problems.
Originally Posted by DaX
Lastly - oils. R134a needs PAG oil, correct? Is PAG 100 acceptable for EG Civics with R134a systems? How about for EF Civics with R12 systems that have been converted to R134a?
Generally, PAG oil for R134a systems, and ester oil (which is mineral based) for R12. Different compressor manufacturers require different oils, which speaks to one of your reasons for flushing the system.
It will usually be listed on/with your new compressor what oil it takes. On imports, they generally call for PAG 46. Parts stores usually carry 8oz bottles of the various kinds, ester oil and PAG 46, 100, & 150.
04-28-2019, 02:10 PM
Blown condenser fan fuse, AC gurus help
