I have a 1990 740 that has already been retrofitted for r134a and the A/C hasn't worked since I've owned the car. My friend had half a can of that AC Pro stuff and I put some of that in hoping it would fix it. The can had probably around 5 or 6 oz of refrigerant in it. The A/C compressor clutch comes on now, for 5 seconds or so and then turns off again for a bit. The vents now blow slightly colder air (maybe 5 degrees colder). The gauge on the AC Pro showed the pressure got quite high while the compressor was off and then drops down to below full when the compressor is on. Do I need more refrigerant? Thank you!

 

I would suggest you get the system looked at. You should get a leak test done to see if you are leaking freon . I suspect this is your 1st problem and after you fix the reason for the leaking then you'll need to see if you have any other component failure. If you have the all season system it is more complicated but if you have the basic system it is pretty easy to diagnose and fix. Buy the way the repairs are not cheap and usually will run between $500 - $1000. Also you need to be careful on handling freon as you can get hurt. See a pro or run with the windows open.

 

Volvo 960 airco specifications service manual has some useful stats in it. This is for the 960 but the pressure values should be similar for any R134a system. I agree with Jagtoes that you probably should have the system professionally serviced since if it leaked out once, getting it charged will be temporary and it'll leak out again. On these older cars the o rings can fail or worse case its the evaporator. A proper service may also involve a new orifice valve and accumulator (assuming the system had to be opened to address leaks) then the tech will apply a vacuum to pull out moisture etc and suck in the proper amount of oil/refridgerant. Also curious about how the conversion was done ie drain/fill (guaranteed to leak) or components from a newer model were swapped in and all new seals were installed...

 

I know those cans have leak stopper in them as well. The can of AC Pro was put in like a week ago and my A/C still comes on like it did last week. I believe the retrofit was done by Volvo themselves at some point as there was a sticker that said it had been retrofitted and it had the Volvo logo on it. I don't have the money to get it professionally repaired right now and I would rather spend $35 on a can of EZ Chill every year or so $500 at a shop... would filling it fix my problem, at least temporarily? I'll have it professionally looked at sometime down the road.

 

I've done a fair amount of research on this problem (it doesn't seem to be very common), but most of the time when the compressor kicks on and off like mine does, it's due to low refrigerant. Some of those DIY recharge cans come with leak stopper in them that's supposed to not interfere with any of the workings of the system. I think I'll try with the recharge cans for now and if the issue comes back I'll get it looked at professionally. Thanks for your advice!

 

I put some new refrigerant into the system a little bit ago (18 oz.), and now my A/C compressor is on most of the time. It still clicks off but stays on much longer. The vents now blow cold air instead of warm air. When the compressor is on, the pressure in the low side drops slowly until it reaches below full on the gauge and then turns off and rises back to the correct level. When the compressor is on, it stays in the blue (full).

 

oh one other thing, the next time you need to top off the system, buy a refil kit with a quality pressure guage (or see if Autozone etc loans/rents one) then google for an R143 temperature conversion chart for AC pressure. what you read as the system pressure when is 60F ambient temp is going to be very different at 90F... if you didn't take this into account when you did the first charge, its quite possible you under-charged the system.

 

Cycling of the compresor usually indicates low freon level. In order to check it you should have a set of gauges hooked up to the sytem. Using the top off can can solve the problem for a little while but it will be shorter then a year. The other concern here is if you overfill the system which will create problems that will render the system useless. Read the info on the net regarding gauge pressures and temperature . Unfortunate a lot of DIY'er who aren't familiar with AC systems get hurt. So be careful when you go through the fill process.

 

​​​​​I found a site that said the AC system contains 44 oz of r12 which converts to about 40 oz of r134a. I know there's at least 16 oz or so. Is the compressor supposed to stay on in this car?

 

the compressor should cycle on/off depending on the temperature setting. at max cold on a hot day, it runs continuously. if the AC pressure gets either too high or too low, it shuts off.


the only way to know how much refrigerant is in the system is to evacuate it, pull a good solid vacuum, then add the correct amount.