AC barely cooling

My 2000 bmw never had great ac, but this year it's been working OK with cooler ambient, but doesn't get very cold at all in summer heat. Compressor is engaging, condenser fan works, etc.

I put one can in with a parts store fill kit, and it seems a little better,  but still only 73 deg at the vents with 90 degree ambient. Needle was just below target zone before adding and in the lower third of the target zone after 

Any harm in throwing another can or partial can to get the needle more to the middle of the target zone?

I know the cheapo gauge is suspect and all.

My 1999 miata had same issue last year,  one can in and it was back to ice cold,  and still good a year later. Was hoping for a repeat of that outcome!

You need to know what the high side pressures are before you add more refrigerant.  Like to see at least 30psi on the low side, maybe 2.5x ambient temp for high side.  Also make sure that the condensor isn't covered with leaves and if you have an auxiliary fan in front of the cooling stack that it is working.

Does your BMW have a clutched compressor or a computer controlled variable unit?  BMWs with the computer controlled variable compressor will freeze you out.  I saw 34F duct temps on a Z4 with that setup.

In reply to sevenracer :

If I suddenly found myself in your situation, I'd be adding another can.

Check the pressures first!

Could be a sticking expansion valve.......also make sure the little capillary tube for the expansion valve is still in place on the evaporator.

In reply to MiniDave :

Memory... some BMW expansion valves actually will buzz and make all sorts of racket when the refrigerant is low.

It's not a feature, it's a bug, but it can be a very useful bug 

Get this from Harbor Freight:

If you have a scan tool, you should be able to read the high side pressure with data, no need to buy parts.

The gauge set is nice if you need to add a small amount of refrigerant, though.

90 degree ambient should be like 45 to 50 psi on the low side. 

In reply to Pete. (l33t FS) :

This is a 2000 model year car (z3m). it's just a clutch actuated compressor compressor and dont think it has scantool pressure readings.

Aux fan for condenser is working. Don't think there is any debris, but will take a closer look.

Looping back to this...and I've managed to make things worse!

Bought the HF gauges. Seemed to be starting at status quo, Compressor and condenser fan running - AC barely cooling.

I hooked up the gauges, started the car, AC on high and opened the valves to the gauges, and both gauges went to like 110+ psi. So, I shut it down right away, and re-evaluated - could not see anything wrong, but was concerned somehow the hammer store manifold was connecting hot side and low side. Also, the HF gauges were on special with 2 free self sealing cans of R134, great! - but manifold kit had no valve tap for the cans, which meant I would not be able to use the manifold to add r134a.

So, trying to press on, I connected the cheapo filler to the cold side and the manifold to the hot side. With this setup, things looked normal. Low side at about 35psi, and hot side at about 150 - classic low refrigerant symptoms. I attempt to add refrigerant, but after several minutes with two different cans of R134a, the gauges don't move. So, grabbed a scale, and the "used" new can weighs the same as a new one. Looking at the cheapo filler - it does not appear to have a pin to open the can.

Undeterred, I brought out another SUPER DUPER cheapo filler I also had laying around. Hooked it up, and crap ...with AC running, low side pegs the gauge over 100 psi - about the same as high side. Just like the first time I connected the manifold. Temp at the vents is ambient+. I also noticed a burning rubber type smell. AC belt and compressor are turning.

Thoughts?

Equal low and high side pressures - seems like dead compressor - but it wasn't dead before I started messing with it. Could it be a failed clutch?

Also, the car had been idling quite a while through all this - is it possible something overheated and changed the behavior? An AC over temp switch or overpressure would prevent the clutch from actuating, right? That does not appear to be what is happening.

Ugh... what have I done 

Yes, when you open both valves, you connect the high side to the low side.  Leave the valves closed if you are just watching pressures.  When you connect the center hose to the refrigerant can to add refrigerant, you only open the low side, with the A/C running, so the low side draws refrigerant in.

The lines themselves will hold one to three ounces of refrigerant.  When you disconnect the gauge set, disconnect the high side first, then you open both valves (with the A/C engaged) so as much refrigerant in the lines as possible gets drawn back in through the low side.  Then you disconnect the low side and close the valves.

This guaranteed loss of refrigerant is why I prefer to check pressures with a scan tool if possible.

An aside, if the gauges don't do anything until you open the valves, the manifold set is designed wrong.  If so, that's a crying shame, as the HF set costs almost as much as a set from a tool truck.

I'm guessing the compressor is short-cycling because the refrigerant is low.  You need to add more when it cycles on again, which it will probably do on its own eventually, but you may need to cycle the switch to convince it to try.  Once it cycles on, the low side will drop quickly, you need to open the can then.  If it gets too low, it'll cycle off again.  Shut the valve to the can off again and wait for it to cycle once again....

I literally just learned this a week ago.

Don't open the gauge valves.   They are already open to their individual ports.  Opening wither gauge opens the lines to the middle.  Opening both opens both to the middle and your pressures will read the same.  Don't do this.

If aucking freon in, open the low side.  If too full and expelling freon, open the high side.  Put it in a bucket or something. 

Pete. (l33t FS) said:

Yes, when you open both valves, you connect the high side to the low side.  Leave the valves closed if you are just watching pressures.  When you connect the center hose to the refrigerant can to add refrigerant, you only open the low side, with the A/C running, so the low side draws refrigerant in.

 

The lines themselves will hold one to three ounces of refrigerant.  When you disconnect the gauge set, disconnect the high side first, then you open both valves (with the A/C engaged) so as much refrigerant in the lines as possible gets drawn back in through the low side.  Then you disconnect the low side and close the valves.

 

This guaranteed loss of refrigerant is why I prefer to check pressures with a scan tool if possible.

 

An aside, if the gauges don't do anything until you open the valves, the manifold set is designed wrong.  If so, that's a crying shame, as the HF set costs almost as much as a set from a tool truck.

Read this again and understand everything he is saying.  Then read it again.

Right, so operator error on the manifold valves. Makes sense. I assumed the center port only connected to the low side - cause why would it ever need to connect to the high side. Oh yeah, maybe need to pull a vacuum on the system or purge lines if you were addressing the issue the correct way!

And to think I watched 80% of 2 whole Youtube video's and even only on 1.5 speed - and still missed that detail, lol.

I bet you just need some refrigerant.  I did exactly the same thing as you did a few weeks ago.  This is how I learned to NOT open the valves to the gauges.

I think you just need this:

https://shop.advanceautoparts.com/p/certified-a-c-pro-certified-a-c-pro-auto-air-conditioning-r-134a-can-tap-certdv134-6/11957918-p?product_channel=local&store=5870&adtype=pla_with_promotion&product_channel=local&store_code=5870&&&&&gad_source=1&gclid=CjwKCAjwqMO0BhA8EiwAFTLgIOMeDjo1MKTpy75GomRhwLeLyfUBgLBlp0EQ2BrSX9ygfNjfAq833RoC1IsQAvD_BwE&gclsrc=aw.ds

In reply to sevenracer :

Hold the can upside down too, while filling.  That way it pulls in liquid refrigerant, not just the vapor.

Indy - Guy said:

In reply to sevenracer :

Hold the can upside down too, while filling.  That way it pulls in liquid refrigerant, not just the vapor.

I'm not sure you actually want to do that.  I have *heard* that the compressor doesn't like trying to compress an actual liquid.

What I have seen is a slight waving of the can back and forth like a pendulum (in the upright position).

wvumtnbkr said:

Indy - Guy said:

In reply to sevenracer :

Hold the can upside down too, while filling.  That way it pulls in liquid refrigerant, not just the vapor.

I'm not sure you actually want to do that.  I have *heard* that the compressor doesn't like trying to compress an actual liquid.

Correct, as far as I remember.  You do want to flip the can upside down at some point if you have one with the oil added in the can, though.  I think the directions are usually to do so when the can "feels light"

I took another stab at this over lunch.

Not looking good.

Using the manifold correctly (valves on the manifold closed), I am seeing 85-90 psi on both low side and high side with car off.

Turn the car and AC on, compressor clutch actuates, starts spinning, but the needles barely move if at all both low and high side. Rev the engine - no change.

So, compressor seems completely shot now? It is possible the clutch is burnt up? I am noticing a burnt clutch/rubber smell.

We're heading out for vacation tomorrow morning, so I don't have time to go any further troubleshooting for a while.

If too full it cant do its job.  

Whatever valve system it uses to transition the high side to the low side could be buggered.

Or, yes, compressor.  Should be able to look at it and have someone turn the AC and see if it engages.

May be other causes, but those are the top of my head 

Separate from a refrigerant issue, on this era BMW if the coolant valve feeding the heater side of the HVAC system fails open the AC can't overcome the heat. Check the lines in/out of the valve with the car running, up to temp and HVAC set for max cool.  Theoretically the control circuit could be faulty too, but the valve is a known failure item.

(I had one once that was OK-ish at low speed, but at highway speed would gradually heat up to "unbearable." After replacing the valve I realized it had been degrading at low speed too.)

part number 4 in this diagram:
https://www.realoem.com/bmw/enUS/showparts?id=CL93-USA---Z3-BMW-Z3%20M&diagId=64_0203

Burning rubber smell with both pressures being equal sounds like a compressor locking up.  If it is overfilled with refrigerant or oil as many of the cheaper cans come with oil, die & seal conditioner added in can cause this.  You likely need a compressor but pulling everything out of the system & adding the correct amount may help 

A couple more details.

When I got the car 10 years ago,  I had the compressor replaced by a shop I trust.  The system has not been opened up since then. So, I think it was loaded with the correct amount of freon and oil.

I haven't actually added any freon to it yet- or oil or dye, but certainly a little bit has escaped as I've messed with it.

The compressor was working and the system was cooling some until yesterday.

I'm thinking that accidentally equalizing pressure between low and high side while the compressor was running caused something to fail.

And just to confirm - the clutch (the spinny bits in front of the pulley) are locked to the compressor shaft,  right? If they're spinning, the compressor is spinning? If so, the compressor isn't locked up. The belt doesn't appear to be slipping on the pulley.

In reply to sevenracer :

I think your clutch isn't engaging, and you are too low for the pressure sensor/switch to activate the clutch.  Add a can to the low side port is my suggestion.