The FAQ section on a/c probs is very good at these kinds of issues...After reading through them, it could be a number of issues. Did you do the work yourself? Use leak detector dye? Change all the seals? How long was the R12 out of the system? The chemical composition of R134 has smaller molecules than R12 and is more prone to finding leaks in the system. You've got more problems here..Too much 134..Is the system "balanced?" What year is your car?

You should have around 32 oz of refrigerant in the system for an R134a conversion. And that is on the upper end.

The R134 conversion banks on about 80% of the R12 capacity. Given that, you'd be looking for 32 oz or maybe one or two either way (I think system capacity is 40oz or around there). The best way is to charge by pressure with a high/low manifold set. Unfortunately that isn't always practical or possible for some people to do, so getting as close to what you think the charge would be is crucial.

The old R12 charging rules are out the window with R134. If you overcharge it even very little, the system will blow warm air and it will also blow something up eventually.

As a rule of thumb, you should strive for 2 or 2.5 x ambient air temp for the high side pressure, when a gauge is available. That is only for the R134a conversion, however, not a factory R134 system.
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1992 940 wagon, 72k
as well as others.

He's talking about the expansion tube but I do not know if your 700 uses the expansion valve or the tube. You can't be compressing the refrigerant, then expanding it and not have cooling, although the heater valve is a good idea. With the heat off (AC off), is hot air made? Is the compressor not compressing? That you find out from the gauge pressures.
You also have to dump the heat resulting from compression to the surroundings and need a clean heat exchanger, the condenser, so remove debris and dirt with a hose.
I suspect the compressor is bad and the high side pressure might be no different from low side. Hope it is the heater valve though.

Could check your heater control valve ive heard of one never seen or checked on it, I myself have done 2 diff types of conversion's to my volvos one the volvo way one the oem way, the oem way blows way colder then the volvo way but they both work, both my ac compressors when the kick on with full oil make a clikcing type sound the entire time they are on ( id call it more a grinding sound but thats me ) you also could check to see if you have a leak somewhere, also there is this little thing i had to replace in one of the pipes long yellow/ white thing make sure you put it in the right direction or it wont get cold, otherwiswe it's got to have something to do with your compressor if all elese fails.