So I think I overfilled the AC

Wife and I have noticed a drop in AC temp on her 97 miata so I figured that I might be able to fix it with a quick recharge.

I purchased one of the proper kits with the can and trigger system from Interdynamics at my local checkers.

I followed the instructions last night for refilling and the system seemed fine.

Wife took the car in today and said that the AC was causing quite a drag on the engine and that there was a sputtering noise coming from under the hood on the passenger side of the car. Close to where I did the refilling.

I have not had a chance to drive or hear the car yet, I will be able to late tonight.

Two questions-

1. Can she drive home with the AC on, we live in Phoenix and it is supposed to hit 110+ degrees today.

2. Is it possible for me to fix, is there a vent or something else I can do. When I did the recharge the guage on the system never showed that I overfilled.

I overfilled my p5 when I charged it. I just used a small screwdriver the open the schrader valve (like how you'd let air out of a tire) until it was back at the correct pressure.

Also, a properly functioning miata AC system does cause a noticeable loss in power.

True, is is the extra noises that we are worried about.

I don't have access to the car at this point so I want her to feel ok about driving home (1 hour commute) with the ac on, I don't want to damage anything.

Properly charging an AC system is a bit tricky when not just filling an empty system (just fill the spec amount). The proper way involves checking the temp drop across the evaporator I believe (considering temp and humidity).

Because of the outside temps involve and the potential for very high high side pressures, there may be a danger of blowing a hose or damaging your compressor. She MIGHT be able to cycle the AC on for a short burst to avoid letting the pressure build up to much, but I am not sure this is entirely risk free either.

If you do the "leak" thing, try not to admit that to any "official" type people. Definitely not EPA legal, but without a license you are pretty unlikely to get in trouble. Probably the best way to do it in that case would be to get a good thermometer and slowly leak down until a good temp is found.

If it is overcharged, you'll probably lock up the compressor if you run it too much.

I got to the car this afternoon, i did vent the system, since it is the newer refridgerent there is actually not an issue with venting, if it was r12 I would be going to a shop.

When I first turned on the car before venting the compressor made a large noise upon hitting the ac button. I vented it a bit more until the system started to cool again a bit.

I drove with it on for awhile and I could feel the engine surging, like the ac was turning on and off. Later tonight when I went out for dinner I had the top down and could hear a bit of a whiring noise when the ac is engaged.

In other cars I've worked on, if you overcharge the system, the compressor will shut off automatically if the pressure is too high by means of two or more pressure switches. Theoretically you won't damage anything because the system just won't run for more than a few seconds before shutting off again. You won't get any cooling of course if this happens.

If you're going to mess with A/C, go buy yourself a good set of gauges. My guess is you should be able to get them for no more than $75 bucks or so new. You can probably get cheaper ones, but I wouldn't.

Then, if you don't already have one, get a shop manual for whatever you're working on. I happen to know from 1st hand experience that the Miata shop manual has very detailed descriptions of proper operating pressure ranges and troubleshooting procedures for the A/C.

Depending on what kind of car you're working on, You'll also want to make yourself an inexpensive wet bulb/dry bulb thermometer setup. (You could also buy one, but that's not grassroots. ) It helps with a Miata, as the manual has a graph that tells you normal temperature from blower inlet to dash vents for a given relative humidity. That's how you do the final check of your work.

Saving yourself one trip to a pro will pay for the gauges and manual, and you won't be trying to fix something 3/4 blind.

BTW, it is perfectly normal to feel a Miata's A/C compressor kick on or off.

InigoMontoya wrote: I got to the car this afternoon, i did vent the system, since it is the newer refridgerent there is actually not an issue with venting, if it was r12 I would be going to a shop....

Umm, OK, go to the EPA and explain that to them. I agree though, it is a very minor thing (R-134 is much less reactive than R-12, but it still is). ANY venting is considered bad (illegal) by the EPA.

Oh, and duhhh, I forgot about the high pressure switch, and yes, when the AC cycles in a Miata (99 version in my case) you can definitely feel it, and hear it also.

16vCorey wrote: If it is overcharged, you'll probably lock up the compressor if you run it too much.

That just happened to mine. It was too late when I noticed it was overfilled. Now it's making a grinding sound.

I actually fixed this earlier today.

I hooked up the original can with gauge to the low pressure port, it did read high (like in the 70 PSI range).

Used a screwdriver to vent it (put it in a plastic bag and inhaled so the EPA cannot come after me ).

After it got back into the 40PSI range everything seems to be just fine. No more compressor noises and the air is noticeably cooler. You might try checking the pressure gamby.

Yeah..i'm trying to figure out the AC in my girlfriend's '98 Grand Cherokee...reads high on the low pressure side of the compressor, compressor clutch cycles off when it gets to the "warning" area of my cheapie gauge on the . Haven't filled it or anything, I wonder if there might be a blockage in the system. A/C Troubleshooting is teh tricky.

InigoMontoya wrote: I actually fixed this earlier today. I hooked up the original can with gauge to the low pressure port, it did read high (like in the 70 PSI range). Used a screwdriver to vent it (put it in a plastic bag and inhaled so the EPA cannot come after me ). After it got back into the 40PSI range everything seems to be just fine. No more compressor noises and the air is noticeably cooler. You might try checking the pressure gamby.

I already bled it down to "normal" level (according to the gauge on my recharge canister), but it looks like the damage has already been done. It's noisy when it spins, but it still blows cold.

Car is a POS, so I'm not too compelled to fix it ASAP.

I am noticing more noise from mine as well. Actually I am getting I think some belt whine, it sounds like the car is supercharged now