so following Klaus C's again excellent advice, added (1) can of R134a to a/c....compressor now cycles much more normally, and air is much cooler, but not quite coooooold...could I need an additional amount of refrigerant?..kit came with a gauge, what should the normal operating pressure be? should this be checked statically, or with a/c operating? again all, much gratitude...

#1 Never check the pressure without the AC running. Static pressure can build to 300+psi depending on the heat.

Your system holds around 26oz of R134a. If you over fill the system you could make things worse. But, you didn't know how empty the system is.

I used to add until the return pipe from the evaporator, at the firewall, begins to sweat like the other pipe. Grab both pipes with one hand whill addin gas, you will feel when the pipe starts to get cold. Remember to have the blower on high.

You could check the temp at the vents, it should be at least 20F degrees cooler than the outside air. This isn't an American car that blows at 35F and mixes heat to get the temp where you want it.
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My name is Klaus and I am a V♂lv♂holic

I've recently recharged the A/C in the '95 854T. Here's what I found...

Yes, check the pressure only when the compressor is running. You are fortunate to have a gauge. There is no "set" pressure because the pressure will vary with ambient temperature. With the ambient temperature of 80F the running pressure should be between 40psi and 50psi. Those numbers will go up as the ambient temperature goes up. I tend to go with the lower side and get 50F air from the vents.

I rarely disagree with Klaus, but this time I do - respectively of course - as follows:

1. Spend the couple of extra bucks and get a gauge instead of "grab both pipes" method. You've already done this so it doesn't apply. The bottom line is that it is impossible to tell what the pressure is and what volume the system contains by noting how cold the pipes feel.

2. I believe the 20 degree difference applies to home cooling systems and not automobiles. An automobile A/C system should chill the air to somewhere around 40F - 45F.

3. I don't know anything about an S70 system, but I know the one in the 854 with Electronic Climate Control (ECC) does blend warm and cold air to reach the desired temp. The A/C workings only know one temp. which is as cold as the level of refrigerant will get. In other words, the chilled air temperature will not vary unless heat is added to it.
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"Differences of opinions should be tolerated, but not if they're too different' - Sharon Craig

You are correct. I just try to keep things simple and easy to do. Most of the 'gauges' that come with R134a kits are not accurate and they have green, yellow, and red levels which are meaningless except to tort lawyers.

I suggested to feel the coolant pipes only because that worked for me. When it is 90F+ and the car interior is 150F+, I don't want the compressor to cycle and the added pressure of around 60psi ensures that. If the system is cycling and the output from the evaporator is warm, then there is not enough gas in the system to make the interior cold.

I initially went to an AC shop and they vacuumed the system and added 26 oz, as per spec, and the system only worked for one day. I did have a leaky evaporator. After I used the 'cold to the touch' method, the charge would last for a month.

I did overfill it once, before a drive to Columbus, OH, when the temps were 65F here and 85F down there. The car ran great until I parked it in the hot parking lot for 4 hours while loading my daughter's school junk. After starting the over hot car, the compressor made grinding noises and then a huge BANG! Green fluid dripped down from the engine and puddled. I thought I lost antifreeze until I watched the liquid evaporate. The high pressure valve popped and then closed. I still had enough R134a to make the return trip.

The system will cycle on so long as the pressure is above 25psi, or so, and turn off at about 18psi. If the psi is over 40 while running, the clutch will not disengage - per the pressostat - but it will if the control unit selected temperature is reached.

Unlike American systems which blend hot air with the AC, the Volvo method does not do that as far as I know. If the ambient temp is lower than the selected temp, the compressor will not engage and that allows the driver to keep the AC switched on year round.
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My name is Klaus and I am a V♂lv♂holic

thanks again to you both...cans of R134 in the kit I purchased are 12 oz each...can you add a partial amount? would use the rest to retrofit my '91 chevy truck with also very warm a/c...fill kit hose/gauge has screw down valve built in, believe it would seal can until rest of refrigerant could be used...thoughts?

Your 91 chevy has an R12 system. Consider having it fixed rather than converting it to R134a which is not as cold.

As to storing a partially used can, the seal on the valve is not that good and the gas will eventually leak out. Perhaps keeping the can in a refrigerator would help to reduce the pressure... never tried that. While the price of a 12oz can has gone up the last few years, consider buying some in October when the big box stores put them on sale for $8.

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My name is Klaus and I am a V♂lv♂holic