I have a 2014 Challenger R/T 6 speed. The A/C compressor clutch never disengages causing the lines to freeze even when the heat is at full blast. I have a scan tool and can see that the PCM is sending a on/off signal. The only way to get it to turn off is to unplug it. I'm sure its grounded somewhere after testing the wires. Looking at the schematics there is no relay for the compressor. I think it may be in the relay box as that's where the signal from the PCM runs to. But with it being a circuit board inside of the box it seems unlikely that's where the short is. Has anybody had this issue? Or maybe somebody has a better schematic for the compressor that will help.
Grounded A/C Compressor
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So when you say, "...causing the lines to freeze even when the heat is at full blast.” do you mean the evaporator is freezing over? It would be nearly impossible for the lines carrying the refrigerant to/from the evaporator to freeze.
On the other hand, having the evaporator freeze over can happen when a “superheat” condition has been reached within the system, and an A/C compressor that continues to run without cycling off could induce ‘superheat’ I do believe.
If that is what you meant in your original post, then that is definitely a problem in and of itself. However, I do not believe you would be able to prevent or reverse that condition by setting the temperature knob to Max-Hot while the A/C is engaged. So I don’t think it is significant that your heater does not have an effect on this freezing condition, as that is actually how the system is designed (the air goes through the evaporator and is cooled down before it is routed through the heater core to get heated up).
But let’s not get too far ahead of ourselves just yet… There are a couple more details I think are missing and should be filled in if possible:
1) Can you hear the clutch on the A/C compressor engage when the engine is running and you turn the A/C on?
2) If so, then you are saying after that, once engaged, you never hear the clutch disengage until the engine is turned off, correct?
3) You said you had a scan tool capable of real-time data display. Can you use that to check the high-side PSI numbers for the A/C system when it is behaving like this?
4) If so, what is the pressure on the high side? Is that output value a steady PSI number, or is it continually climbing as the compressor continues to run?
5) What is the service history of the A/C system in the car? Unknown, never serviced, serviced but by a certified tech, etc.?
6) Are you able to get your hand back behind the engine so that you can use your fingers on one hand to take the relative temperature of the 2 refrigerant lines coming out of/going into the firewall (on their way to/from the evaporator)?
7) If so, what are the lines’ relative temps (relative to each other) after the car is running and the system has been on for a while, continually cooling (or trying to)?
That last little manual test of the temperature of the 2 a/c lines in relation to each other (both about the same, one colder than the other, one hotter than the other is actually a very informative test with respect to how the system’s health is overall. If both are about the same temp, it is healthy; if one is colder than the other, the system is NOT healthy, but what ails it is a whole separate discussion, so let’s focus on one thing at a time…
If you are able to provide some clarity/more details on the issues I laid out above, I think we will be better able to troubleshoot from there (or realize it is beyond our capabilities to diagnose). Either one is preferred to the current status, I'm sure :wink3:
Plus, those members who are certified techs and such that could help out here might be more inclined to chime in once we’ve got a more clear picture painted of the situation :SM002:
nuke
This is the data with the car after it warmed up some with the A/C off. Both lines are cold to the touch. The PSI will climb to about 160PSI then fall again. after driving it it was steady at 148PSI. The volts will climb to about 1.75. The evaporator core does freeze over but the Low pressure line freeze all the way to the compressor. It is worse on long drives. The evaporator core will completely freeze blocking all the air passing through it and nothing will come through the vents. The compressor never cycles, it is always engaged. The A/C was serviced last summer because of the same issue. They found that it was over charged and vacuumed/recharged it. It seemed to be fine after that but then it started acting up again. At idle everything seem to work fine except the compressor. While driving it will completely freeze over. I've had it freeze over then pull into a parking lot wait 5 - 10 and it will unfreeze and I will have A/C again. then a mile down the road will freeze again. This was even after it was serviced.
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Does the behavior change at all when you put it into recirculate mode versus straight through? Also, what is your geographic location, somewhere with very high temps but low humidity by chance (Pheonix, Midland-Odessa, Hell)?
Realistically that may not matter, but I am curious. Either way, the compressor should kick off when the system detects imminent freeze up at the evaporator and most certainly after it has frozen. So the fact that yours is not would lead me to suspect the temp sensor on the evaporator. Can you get a live reading of the voltage of that thermosister while this is going on? That should verify it as a problem or eliminate it as the culprit if it isn't at fault...though I don't see how it could be operating correctly (or its reading is being received correctly, if there is a prob with the wires going to it) if the compressor is still going long after it should have detected a problem and been commanded to tap the brakes.
The high-side pressure can be a good data point to use in diagnosing some issues, but I don't know that it helps much here (other than to indicate the problem is not a certain subset that would lead to out-of-range values). The actual amount of freon in the system is the only true data point that can say whether or not it is over/under charged with freon, and you would need a setup that can evacuate the whole system and weigh it to arrive at that one, so I'm guessing we're out of luck there. However, neither an overcharge or an undercharge seem likely here, especially given the system's recent servicing by a professional (assuming they knew what they were doing and didn't fill by gauge pressure alone and vacuumed out the system before-hand to remove any non-refrigerant air).
Speaking of air, there is a possibility that contamination from regular old air is at play here, but if that's the case, and especially given its recent service, there would have to be a leak in the system somewhere that allowed it get in. That's a whole 'nother issue that will likely require a pro to diagnose further.
Having said all that, I still keep coming back to the fact that the system isn't engaging its usual safety-valves when a fault is present, namely that the compressor should kick off when the evap freezes over. So if you can find some what to verify what the evap temp sensor is sending out, that would be the next logical step I believe. It is a thermosistor I believe, so you will only find a voltage reading, but that's enough. It should vary with temperature, and so when the evap freezes it should be the polar opposite of what it reads when first coming online (I forget if those things are inverse or verse when it comes to their readings versus their measured temps, seems like it's inverse, but who can remember).
I finally found the ohm rating of the compressor. It is suppose to be 3.5 ohms. Mine was at 5.8 ohms. Turns out it is grounded at the compressor. There are no visible frayed wires so I suspect it is internal. I'm going to replace the compressor. Ill give an update on how things turn out for anybody with the same issue.
Good to hear you identified an off-nominal electrical condition to help diagnose further. Given that changing out the compressor is a pretty involved task if doing yourself and a relatively expensive job if paying someone else to do it, if this were happening to me, I would want to make absolutely certain the compressor itself was the problem and not some wiring connection or plug that connects it to the wiring harness. Doing a series of voltage drop tests on the various wiring connections and circuits involved here should eliminate the wiring harness connections as the culprit here, and it would not cost anything but time if performed at home. That's the approach I would take anyway, if I were similarly afflicted...
Either way, I hope you can get it figured out and resolved asap, as I know what it's like to go without an a/c and that's a special kind of hell that no one should be subjected to!
Be sure to update the thread with the outcome, as I'm sure the eventual fix and any other steps taken to apply it will surely be useful to others who might encounter similar problems in the future.
Nuke
I found the problem finally. It was the relay box. After all the probing and testing we found out it was grounded in the relay box on the circuit board. Replaced it yesterday and everything is fixed. A/C cycles and is nice and cold. I suspect it was an issue from the factory but I never noticed it unless I took it on a long trip and its out of warranty. But it was cheaper than replacing a compressor.
The relay box? Is that the under-hood fuse holder or something different?
Good to hear you finally got it, and especially without having to replace the compressor and all the other tasks that come along with that in an a/c system. That could have been one expensive, unnecessary uh-oh if you just started replacing parts right off the bat. :thumbsup:
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