I am going crazy trying to find this thing. I don't believe it is the shrader port on the receiver drier, because that is giving me the same reading as the low side. Which makes sense because it is just a few feet before the low side port.
Man this is strange.
Thanks

 

I had the same problem on my '91 740. Turns out that there is no port on the line, it's on the compressor, which is definitely not one of Volvo's better ideas.
Kind of a PITA to hook a gauge to and to make matters worse, some replacement compressors, such as the one I installed last summer, angle the schrader valve in such a way that it is blocked by the high side line. The guy that makes my AC hoses says he can install a fitting in a more accessible place next time I have to evacuate the system. You might want to explore this if your system is discharged already or if you're going to be evacuating it to fix a leak or whatever. Good luck with it..

 

I will look and see if I can find it. I'm going around and around with this ac system. I have replaced the orifice tube and the receiver drier. The system is holding a vacuum. I can get to around 38F at the vent, IF I hot wire the compressor. As it stands I'm thinking its either the temp switch in the gauge (the soldier that goes bad) or the high side pressure switch. The thing is when it's hot wired and blowing good and cold, the condenser fan does kick on and off as supposed to. So I need to have a look at the high side pressure and see where its running at to see if there is a problem.
Thanks

 

"How can I tell if the compressor is bad?

Usually the compressor will show the inability to generate enough suction and pressure at or near idle speeds.

If engine speed needs to be substantially increased to bring pressures in range, that's a sign that the compressor is getting weak. Often the complaint is... only cools when the engine is reved - or - only cools when driving down the road.

Sometimes it's very simple. If we hook the gauges up and see 80 psi on the low side, and 80 psi on the high side, and the compressor hub is spinning, it's likely that compressor is done. It's not producing suction, and it's not producing pressure. We could add or remove refrigerant and still nothing would happen. The compressor must be able to pull a vacuum, and create pressure. Compressors that use a variable stroke are often misdiagnosed as being defective, when only the internal pressure control device is at fault. "

(From another board on the web)

Sounds like I'm running into this.
Once I connected the highside and lowside port, I am getting the same reading 55psi. I put in the 2.7 12OZ cans and the correct amount of oil. Per the stcker under the hood.
It is blowing pretty cool driving down the road. But sitting in the garage with idle at 1500rpm it blows around 60degrees.
Could it be the clutch needs to be shimmed? Or is it the reed valves??????

 

Mine is a 1993 940 Turbo. I need to service the A/C. Is the nut on the back of my compressor shown in the attached photo covering the high side service port? It is right below the high side output connection from the compressor to the condenser. I would like to be sure before opening it up because I don’t want to get freeze-dried.

 

You charge the AC through the Low Side! And that's on the passenger side fire wall drier receiver-a tag should be there.

 

This is my first try at any A/C repair. It is challenging and interesting. I do have a leak. I have located all the parts and the low side service port and studied diagnostics with an A/C manifold, leak detection, evacuation, repairs and flushing. I want to measure the superheat and subcooling. Otherwise I would not know if I were overcharging. For that I will need the high side service port location.

 

The attached 940 A/C diagram shows the high side service port as part #26 located on the A/C muffler pipe on the bottom passenger side corner of the condenser. My vehicle has no muffler and no high side service port at that location.

So, out of curiosity, I removed the plug on the back of my Seiko-Seiki SS-121DS5 compressor (pictured in the earlier photo on this thread) to see if the high side service port was under that plug. It was not, but I did regrettably release what little refrigerant I had left. "Curiosity killed the cat".

So my vehicle does not have a high side A/C service port and never did. To make one, I purchased Santech #MT1609 valve. It screws right into the same location on the back of the compressor where the plug was removed. It is necessary to have your refrigerant responsibly removed before doing this.

My A/C system sticker specifies "Volvo PAG Compressor Oil" as the system lube. The compressor nameplate specifies "Lub. oil: 220 cc SK20". 220 cc is the total A/C system lube required, not just the compressor amount. It is not easy to determine for certain what viscosity SK20 is. Googling, you will find every different viscosity of PAG oil specified for this comprssor at least once. After much online research, I found that SK20 is Seiko-Seiki's OEM specifier for PAG-100 -- for certain. I used double end-capped PAG-100 successfully. It is more expensive, but some research papers report it can better handle moisture in the A/C system.

I had to decide whether I would replace my fixed orifice tube ($1) with a variable tube ($18). My research indicated that the variable tubes are beneficial in hot areas in standing traffic. That does not apply to me, so I went with the fixed.

I was able to evacuate my A/C system to around 900 microns using the Autozone loaner "OEM" brand vacuum pump. That pump will evacuate down to 500 microns or lower, but at those deep vacuums, my inexpensive gauge set leaked, so I had to settle for 900 microns. The downside of these pumps is that they have no check-valve. If you evacuated the A/C system with this pump and then turned the pump off while it was still connected, the vacuum would suck the oil out of the pump and into the A/C system. Very bad news.

My A/C system sticker says charge with 2.07 lbs. R-134a, which I did.

My A/C now produces 46˚F air from the center vent tested with the car sitting in the driveway, i.e. with only the fan blowing through the condenser, at a 73˚ ambient temperature and 54% humidity.

 

Where did you find this ac parts diagram. I need part #14 but can not find it anywhere. I have a 1990 Volvo 740 but when i look up that car it does not show that diagram. The diagram you posted is what i have in my car. The port is bad so changing the Schrader valve is not an option.