AC Compressor Cycling causing idle rpm drop (Overcharged AC) Topic is solved

[styoung94]

Hey. So like the title says my AC compressor is cycling on and causing rpm drops during idle. There is a decent loss of power when this occurs. To provide a little history.

Previous owner ~4 years ago hit something and ruined the condenser and the hose that runs between the condenser to compressor. I replaced both of those this week with junkyard parts. I did not vacuum out the system, as I wanted to confirm that it held pressure before dropping $120 on a vacuum and charge that would just drain out. I added 60 cc of oil, and then three 12 oz cans of r-134a.

The AC blows cold but it cycles on and off causing the rpm drop and power loss. The plan right now is to give it the weekend to see if it still holds and then if it does I'll replace the drier and then have it vacuumed and recharged.

Any idea why the compressor cycling on and off causes such a large rpm drop? I know that the system requires a good bit of energy, but I have not read elsewhere that it causes a drop like this. Would it require additional r-134a, since a sign of low charge is the compressor cycling?

Any input is appreciated. Thanks.

[oragex]

Cycling every few seconds is how it works, dropping the rpm might be either the pulley bearing is about to seize or the compressor itself is about to go. Dying compressor should make some pronounced noise. Try removing the belt tension and turn the clutch plate by hand, should not be so hard to turn, a little resistance is normal. Then kick the pulley, should run without friction noise.

[styoung94]

Thanks oragex. I'll let it cool off for a little bit and then try rotating the clutch plate. What do you mean by kick the pully?

[abscate]

I added 60 cc of oil, and then three 12 oz cans of r-134a.

If you check your R134A capacity I think you will find you overcharged it - which will exactly cause your symptoms.

'kick the pulley' is Canadian for 'check the pulley" They changed this when mechanics took the engine lights off cars, took them to the rink, and smashed them into the boards too many time...when they read 'Check Engine Light"

[styoung94]

If you check your R134A capacity I think you will find you overcharged it - which will exactly cause your symptoms.

Even with having the system fully open and the line from the compressor removed? I couldn't find an exact recommendation for the number of cans to use, nor did I think the pressure in the cans made it possible to over charge.

Any recommendation to ensure it has the correct amount in there other than taking it in? would those cheap cans with the gauges be accurate enough?

'kick the pulley' is Canadian for 'check the pulley" They changed this when mechanics took the engine lights off cars, took them to the rink, and smashed them into the boards too many time...when they read 'Check Engine Light"

Haha I like that, nice and literal.

[abscate]

Look for a sticker under your hood with the AC refrigerant specified. I think its about 750g or so?

750g is about 27 ounces.

A little less in warm climates (5-10%), a little more in cold climates (5%)

would those cheap cans with the gauges be accurate enough?

No.

[abscate]

Looks like 750g for your AC charge in warm climate

[sleddriver]

Hey. So like the title says my AC compressor is cycling on and causing rpm drops during idle. There is a decent loss of power when this occurs. To provide a little history.

Previous owner ~4 years ago hit something and ruined the condenser and the hose that runs between the condenser to compressor. I replaced both of those this week with junkyard parts. I did not vacuum out the system, as I wanted to confirm that it held pressure before dropping $120 on a vacuum and charge that would just drain out. I added 60 cc of oil, and then three 12 oz cans of r-134a.

The AC blows cold but it cycles on and off causing the rpm drop and power loss. The plan right now is to give it the weekend to see if it still holds and then if it does I'll replace the drier and then have it vacuumed and recharged.

Any idea why the compressor cycling on and off causes such a large rpm drop? I know that the system requires a good bit of energy, but I have not read elsewhere that it causes a drop like this. Would it require additional r-134a, since a sign of low charge is the compressor cycling?

Any input is appreciated. Thanks.

You may have over-charged it. Never been down that road before having to re-charge an empty system. When I have to top-up mine (evap leak), I watch the suction line for sweat. Then I stop.

You also have to vacuum out any fully empty system first before re-charging to remove all of the air. Rationalle is you don't want any moisture in it, nor air. Also why you need to purge your recharge hose of air first before charging, to prevent the mixing of air + 134a gas inside the system. Thus, vac'g a system isn't just to check for leaks: It's to boil all the moisture out & remove the air first.

When a car, with a properly working air-cond system does this, there is usually a problem in the IAC motor or one of its hoses.

[styoung94]

Just to updated on what the issue was. It was over charged. I had it vacuumed out and recharged on Saturday, and that fixed the issue of the rpm drops and power loss. Thanks for all the help.

[Clemens]

Thanks for posting the solution.