AC system over-charged and compressor cycling on-off at engine idle ??

2005 Cavalier. As in title, the system appears to be over-charged. And the compressor cycles on-off frequently (every 30 seconds approximately) when the engine is at idle or roughly below 25mph when driving. So no cold air unless I am driving steadily at a higher speed.

Low-side pressure readings in the pics below were taken with both AC and fan speed full on, windows open, engine at idle. The gauge has been tested OK on another (newer) car's system.

Oddly (to me) the pressure is higher when the compressor is off, and comes down a little, although still too high, when the compressor is on.

Questions:

1) can the compressor on/off cycling issue be resolved by simply evacuating some of the r134 from the system, to get the correct pressure?
2) if yes to the question above, can r134 be evacuated from the system by simply pulling the trigger on my gauge/recharge hose when no recharge can is attached? And if I do this, will moisture from the atmosphere be able to enter the system possibly causing other issues?

Thanks....



compressor = OFF
DSC09382 compressor off rs800.JPG



compressor = ON
DSC09377 compressor on rs800.JPG



refill hose trigger
DSC09386rs800.JPG
 
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Refrigeration systems usually have a low pressure switch to save the compressor from burning up due to no refrigerant.
Have not seen a high pressure switch in automotive but I could be mistaken.Usually the low pressure switch is in the lineset in the engine compartment.Two wires, take a meter and see if that switch is opening and closing while clutch cycles.
And no ,as long as the system is pressurized you can't introduce moisture or air into it by letting out a little refrigerant even if you're on the suction side.

Bob

edit-
I've been doing commercial HVAC for years but got away from automotive a long time ago so I did a little research last night and stand corrected about high pressure switches.
GM does in fact use high as well as low pressure switches in their refrigerant lines.
According to GM Tech web info the Low Pressure switch opens around 47psi and the High Pressure at 425psi.
Some also have a "transducer switch"(fancy name for a pressure switch) that control the cooling fan.
 
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Thanks Bob. Interesting idea about the high pressure switch possibility. But even if there is one, it seems to me the system needs to loose some refrigerant.
 
Is the engine cooling fan running when the A/C is on? I'm pretty sure the Cavalier does have a high pressure cut off switch so if the fan isn't running the pressure will quickly shoot up and shut it off.

The pressures look okay for the low side, the running pressure is too high but that would be the case if the fan isn't working.
 
I sent you a PM that includes a bunch of links of which some specify the trip points of various pressure switches.

Bob
 
Thanks guys.

@Eric H Please clarify, are you saying that anytime the AC is on the radiator fan should be running always? Because when AC is off, that fan runs based on coolant temperature and is often not running.
 
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Bleed some of that out of there until the needle is at the top of the green. You are definelity overcharged which can cause compressor failure. I know because I overcharged my car.
 
My 04 Chevy Truck has no max ac setting so the ac compressor cycles on and off its just the way they designed it. My wife's Ford has max ac and ac, with max the clutch stays locked, ac it cycles.You are definitely overcharged and need to bleed some off before you blow the compressor seals.
 
Thanks guys.

@Eric H Please clarify, are you saying that anytime the AC is on the radiator fan should be running always? Because when AC is off, that fan runs based on coolant temperature and is often not running.

Yes, whenever the compressor is running the fan should also be running, there may be a short delay between turn on and the fan kicking in but if doesn't turn on before the compressorkicks off there's a problem.

Without the fan cooling the Condenser the high side pressure will shoot up very quickly until the cutoff switch shuts it off.

Do not bleed off any 134 until you have verified the operation of the fan. It will not be overcharged unless you added some. If you did that then all bets are off but the fan should still kick on in any case.
 
OK thanks Eric, I will see if I can check that later this evening.

Thanks also to JHS2RT & Tim64. My gut instinct is to simply expel some of the refrigerant. But before I do that, I want to be be fairly certain that overcharge is the cause of the too high pressure, and not something else. In one of the links that Bob gave me I found this, which sounds like what Eric is saying:

"Two primary reasons for higher than normal air conditioner pressures include lack of air flow through the condenser and an overcharge of the system. Lack of air flow can result from a bad condenser-fan-motor. A worn fan-clutch or debris blocking air flow through the condenser will cause the same issue." http://www.agcoauto.com/content/news/p2_articleid/257


So I am just being cautious and methodical at this point.


@JHS2RT - What was the behavior of your AC system when it was overcharged? How did you know? Did the compressor cycle on-off too much?
 
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Yes, whenever the compressor is running the fan should also be running, there may be a short delay between turn on and the fan kicking in but if doesn't turn on before the compressorkicks off there's a problem.

Without the fan cooling the Condenser the high side pressure will shoot up very quickly until the cutoff switch shuts it off.

Do not bleed off any 134 until you have verified the operation of the fan. It will not be overcharged unless you added some. If you did that then all bets are off but the fan should still kick on in any case.

I have neither added nor bled off any refrigerant. However, this car had front-end collision repair 3 years ago and many of the replacement parts were from LKQ (i.e. used), including radiator, condenser, and radiator fan assembly. The system would have been evacuated (hopefully) and recharged at that time. Overcharging is, I believe, not uncommon on a system that requires just 1.5lbs. I only became aware of this AC problem recently as I have had my Mom's dog for the past couple weeks, and it is too hot for her right now with windows down only, so I have been using AC more than I would usually.



I was not able to verify operation of the fan one way or the other. With AC on, the fan did not start.

With AC off I let the engine idle for maybe 15 minutes watching my in-dash temperature gauge and the radiator fan. Fan never started. However, the coolant temperature never got very high either. Normal operating temp is around 195F, and while idling the temp never went much above that, maybe a only couple degrees and possibly not enough for the fan to kick in.


A non-working fan might explain why AC works at 30mph, condenser is getting air thus allowing compressor to stay engaged, and fails at slower speeds. Does that sound right?


My next move is to check for trouble codes, although there is no "check engine" light. Don't know if radiator fan has sensors connected to the OBD II system either...
 
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If the fan doesn't come on at idle you will not have any air at all flowing through the condenser coil,thus no heat being removed from the refrigerant thus causing high pressure to rise.
Going down the road forces some air through the coil but not enough without the fan helping.
Just imagine what would happen if you lost the outside condenser fan on a house ac unit.
The high pressure would build up so high as to trip the high pressure switch which saves the compressor from burning up.

Bob
 
Not likely to get any codes.

If fan isn't coming on at all and fuse is good, I'd suspect bad relay first.

Schematic (right side) is for 2004 Cavalier but 2005 might be the same or similar.

1. Pull relay and check for voltage at B12 and A12 (hot at all times). If fuse is good, there should be voltage here.

2. Reinsert relay, turn on AC, and check for voltage on light blue wire to fan. If no voltage here, try a new relay. (Or temporarily swap with an identical relay in the fuse box) If voltage here but no fan operation, relay is good but fan motor is bad, harness/connector to fan is bad (check for corrosion), or fan motor ground is bad. Confirm clean connections and good ground continuity at fan motor.

9AAEE5B4-5DDB-445B-AF20-01527B4D351C-530-000000D8C1C42FDB.gif
 
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If the pressure is cycling between 25 and 45, it looks more like low charge. Thats the typical range for an R134a pressure switch to operate. Pressure will always be high on the low side and low on the high side when not running.

if the fan isn't running though, you will usually have pressures edging towards high on the low side, and way high on the high side. Fan should always run in AC mode. No air across the coil means no heat shedding, so it won't work. If it has a high side pressure switch, it might trip. Nothing I own has one of those, not sure what the operating range is.
 
OK willyrover...


2005 Cavalier is just a left-over 2004 as I understand it. '05 was the first year for Cobalt and there were some unsold '04 Cavaliers that were titled as '05.

no DTC codes present
fuse is good
12.5V at B12 & A12
swapped relays with blower motor and verified relay is good

beyond that I will need to put the car on ramps and get underneath...something I can not do at this moment. Maybe tomorrow.

thanks for the schematic
 
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@gadget73 those red lines on my gauge are simply markers for the target range, which is variable with ambient temperature and I can physically move those lines by rotating an outer ring on the gauge. The black needle is my low-side pressure reading.
 
If it was in an accident it wouldn't surprise me at all if the body shop failed to plug the fans back in, or the wires got damaged, I see that kind of stuff all the time.
 
The reading is with the compressor engaged? Thats closer to what I'd expect if the high side pressure was also much too high. No cooling fan would definitely do that.
 
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