Automotive Air Conditioning Information Forum (Archives)

Saab Nut on Mon May 28, 2012 3:11 PM

Year: 1997
Make: Saab
Model: 9000 Aero
Engine Size: 2.3
Refrigerant Type: r134a
Country of Origin: Sweden

Hi All,
It is getting to that time of year here in Florida to think about my AC. I've noticed my car not cooling as well as it did last summer and I am thinking it needs a charge. The local shop refuses to work on foreign cars (ridiculous) and the last shop I visited for A/C issues on another car pulled the bait-and-switch on me (not returning there!). So this year I bought myself some AC specific tools, like a set of r134a guages and a can-tap tool.
I was hoping someone could walk me through some of the basics. I am a competent DIY'er, but always appreciate the wisdom and experience of others.
Where to start?
Thanks

buickwagon on Mon May 28, 2012 8:38 PM

Lesson 1: to do this legally and responsibly, you need to add a recovery machine, cylinder and an accurate scale. At a minimum. Otherwise you are just guessing about the charge. Spend some free time reading archives of this and other AC forums and you will learn a lot.

-------------------------
I've saved hundreds on service by spending thousands on tools.

mk378 on Mon May 28, 2012 9:22 PM

If you're having to recharge every year, there is a leak, so owning a leak detector could be helpful. See if UV dye has been installed by looking for yellow/green color in the service ports when you take the plastic caps off. If the system has dye in it you can use a "blacklight" CFL bulb in your droplight to look for it leaking out. Do this at night or in a dark garage. Yellow "blue blocker" shooting or driving glasses protect your eyes from UV and improve the contrast of the glow from the dye.

Put your gauges on and get some pressure readings. The standard test is to set the A/C for maximum cold, but leave the car doors open so it doesn't actually get cold inside. Rev the engine to about 1500 rpm and hold it for a minute or so then take readings. Gauge manifold 101: The hand wheels on the manifold must both be closed to take readings. If the quick connect couplers on the ends of the red and blue hoses have a knob on the top, turn the knob counterclockwise before coupling to the car, then turn knob clockwise to open the valve in the port.

The Mastercool book is good for learning and reference.

Edited: Mon May 28, 2012 at 9:28 PM by mk378

Saab Nut on Tue May 29, 2012 11:00 AM

Quote
Originally posted by: buickwagon
Lesson 1: to do this legally and responsibly, you need to add a recovery machine, cylinder and an accurate scale. At a minimum. Otherwise you are just guessing about the charge. Spend some free time reading archives of this and other AC forums and you will learn a lot.

I have been searching the forum here and learning bits and pieces. Unfortunately, the link to the charge capacities database does not include my car. I am more than happy to bring the car to a shop just for evacuation and vacuum testing. Any input into what a fair price for this might be? I've seen it done to my other car before and it is not a lot more complicated that pulling codes from the computer. If a shop tells me they want $120 to do this, I'd just buy a Harbor Freight vacuum/recovery setup. If they want $20, then I will give them my business. Any shop owners or customers want to chime in on pricing?

Saab Nut on Tue May 29, 2012 11:11 AM

Quote
Originally posted by: mk378
If you're having to recharge every year, there is a leak, so owning a leak detector could be helpful. See if UV dye has been installed by looking for yellow/green color in the service ports when you take the plastic caps off. If the system has dye in it you can use a "blacklight" CFL bulb in your droplight to look for it leaking out. Do this at night or in a dark garage. Yellow "blue blocker" shooting or driving glasses protect your eyes from UV and improve the contrast of the glow from the dye.

Put your gauges on and get some pressure readings. The standard test is to set the A/C for maximum cold, but leave the car doors open so it doesn't actually get cold inside. Rev the engine to about 1500 rpm and hold it for a minute or so then take readings. Gauge manifold 101: The hand wheels on the manifold must both be closed to take readings. If the quick connect couplers on the ends of the red and blue hoses have a knob on the top, turn the knob counterclockwise before coupling to the car, then turn knob clockwise to open the valve in the port.

The Mastercool book is good for learning and reference.

I have only had this car 1 year, so I have no knowledge of past ownerships habits.
And yes, I can see indication of UV dye in the service port when I removed the cap.

My guage set manual talks about "static" testing while the car is not running. I followed the step-by-step and the blue dial read +10 on the r134a scale which corresponds to 45psi. The red dial (while scaled differently) also points to right around +10 and 45psi. It is my understanding that these readings should be close during static testing, but I am unsure whether those pressure figures are acceptable.

mk378 on Tue May 29, 2012 12:37 PM

Unless the weather is very cold, 45 psi static means nearly empty. There is not enough refrigerant in the system to have liquid anywhere.

For the most part, ignore the temperature scales on the gauges and just look at the psi.

Saab Nut on Tue May 29, 2012 1:33 PM

It is presently 82* here in Florida, so not cold at all. What kind of static pressures are normally experienced?

buickwagon on Tue May 29, 2012 5:19 PM

If there is any liquid in the system, and it is uncontaminated R-134a, then at 82°F, the static pressure should be a 89.6psig. That is how mk378 can state the system does not have any liquid. The problem is there is no way to determine accurately exactly how much liquid is in the system by pressure. The vapour pressure is the same for 1 oz of liquid or 100 oz of liquid, and the static pressure is the same throughout the system. Manufacturers do whatever math is required to determine the ideal charge and post that on a sticker under the hood. The only way to know for certain that you have the correct charge is to start with an empty system -- meaning completely of any sort of gas including air -- and then fill by weight.

Once the correct charge of refrigerant is in place and the system is running, then the pressures offer guidance to troubleshooting the system.

-------------------------
I've saved hundreds on service by spending thousands on tools.

Saab Nut on Tue May 29, 2012 8:54 PM

Quote
Originally posted by: mk378



Put your gauges on and get some pressure readings. The standard test is to set the A/C for maximum cold, but leave the car doors open so it doesn't actually get cold inside. Rev the engine to about 1500 rpm and hold it for a minute or so then take readings. Gauge manifold 101: The hand wheels on the manifold must both be closed to take readings. If the quick connect couplers on the ends of the red and blue hoses have a knob on the top, turn the knob counterclockwise before coupling to the car, then turn knob clockwise to open the valve in the port.



Performed this procedure exactly. Got 95psi highside, 0psi lowside. Ambient temp 76*, Humidity 79*. No thermometer in vent but would classify temp as "warm".

Could this be indicative of needing a charge or does it point to something else like compressor clutch?

mk378 on Tue May 29, 2012 9:34 PM

Severly undercharged. As it worked last summer, there is a significant leak. You could do the old "gas and go" but it's going to leak out again fairly quickly.

Edited: Tue May 29, 2012 at 9:45 PM by mk378

Saab Nut on Tue May 29, 2012 9:47 PM

So is there any harm in running in a 12 oz. can of r134a? System capacity is 950g (which, my math says is just shy of 34oz.). If she is leaking somewhere, won't the added pressure help me identify the source of the leak? I have seen trace of dye by the service port.

mk378 on Tue May 29, 2012 10:19 PM

Static pressure of 45 suggests there is only about 6 oz left. One can won't be enough to restore operation, it would just be a waste of money. There is always dye near the service ports since some is prone to blow out when the hose is disconnected. Do a thorough check for dye with a blacklight or use an electronic detector. The remaining pressure should be enough to detect.

Edited: Tue May 29, 2012 at 10:20 PM by mk378

Saab Nut on Tue May 29, 2012 10:42 PM

Thanks mk378! I will try to find a blacklight.

Saab Nut on Wed May 30, 2012 10:53 PM

Talked to a former Saab mechanic and he indicated that operating ranges for the low side should be 30-40psi and on the high side 150-250psi. With that info, I recharged system with a 12 oz. can of r134a today. Got the low side pressure at 36psi and the high side up to 230psi before I stopped charging the system. Went for a test drive and the air was actually cool (guessing 55* with ambient temp being 87*).
Got a blacklight and checked for dye tonight. No signs of dye leaks around compressor, line fittings, upper condenser connection or hose clamps. Unfortunately, visibility is blocked to evaporator and lower condenser connection.

Did this possibly solve my problem? Am I forgetting something?

Dougflas on Thu May 31, 2012 8:20 AM

You may be able to check the evap for a leak by shinning your UV light on the drain tube opening. Ypu'll probablt have to jack the vehicle up safely and get under it.