Should a/c compressor cycle on/off while driving?

[wheelsup]

Its a standard fitting and line you can get them at most any auto store. Or back to HF for a good price on one.
In TN I charge after full vacuum pull down. After a full evacuate the system charge gives me roughly 32 low side ( with charge bottle off and system stabilized) and 200 high side. It cycles at idle and at highway speeds and air comes out center vents at 42 degrees when still and 38 degrees when moving.

I felt that the system might be overcharged as well when first putting it in. I bought two cans @ 12 oz each so total of 24 oz. I did not put all of the 2nd can in, left an once or two. Placard on strut tower indicates 1.63 lbs of 134a which is around 22 oz. I can't imagine even if I had used the two cans completely, that 2 oz over would overcharge.

However my low side pressure is much higher than yours, at 38-39 psi. So it's possible it is overcharged.

Of interest. Before doing this repair I simply tried to charge the a/c. Not the best way to fix the issue but wanted to get through another summer with the least amount of work. I added one can and the compressor was running but no cold air was coming out. I added the second can and as I was doing that the accumulator blew out of it's quick release. Low pressure was obviously too high. This has never happened to me before.

I then decided to change the evap. I took the system apart and also changed out the orifice tube in the low pressure line - it was not plugged up what so ever, very little debris. I replaced the evap and accumulator, sucked it down as best as I could multiple times (29" or so, give or take over the course of 30 mins). Attached the can and tap and bled the line to ensure no air in the charging hose and opened the service port. Charged up and the system does blow cool, not freezing cold, but cool air 48* or so.

From what I am reading I do not believe I am dealing with a blockage, as that would indicate as low pressure (although hard to tell without getting the high side reading) in addition to very little debris on orifice tube showing no signs of internal damage (yet). The over pressure while charging before replacement is a new one for me, in the past I've just added 134a and gone the whole summer without issue.

I'm not home under Tuesday night, I will search out that adapter. It looks like I unscew the high pressure switch and some sort of adapter screws on (or does the hose screw to it directly? Looks to be too tall for that. The quick connect does not fit on it). I cannot connect my hose to that so will need an adapter.

I've had good luck with repairing a/c systems in previous cars, flushing the system and charging etc. so I'm not a total newbie at this. Really frustrated this time though.

[JDS60R]

All of the R 134 systems have the standard fitting on both high and low sides.

I would have to have yours in front of me but am guessing the high side will be telling here. It will help you see if you are over/under charged and if there is still too much air in the system.

The standard adapter that comes with all r 134 gauges will fit your system. There is no special adapter needed. It just plugs into the port like any other gas fitting

[JDS60R]

When you pulled a vacuum did you have both high and low sides connected and open to the vacuum source??

[wheelsup]

No, just the low side connected.

I might be wrong here on the adapter. But I unscrewed the high pressure switch down by the accumulator and used the quick connect. It does not fit, I tried several times. Looks like there is a screw on adapter? Or am I way off base here?

[JDS60R]

Well - you found your issue. You need to pull a vacuum with both sides connected and open to the vacuum source. You likely still have air in there.

Please remind me what car we are working on here . was it an 850?

[wheelsup]

Yep a 95 850.

https://www.matthewsvolvosite.com/forums ... 31#p191231

Talks about some sort of threaded fitting.

[JDS60R]

Ok - no standard high side fitting on your car. There is a threaded high port under part 48 but you would need an adapter . In order to pull a full vaccuum you will need to be pulling a while and turning the compressor over a few times. I remember this being an issue on my 95 NA but pulling it down for about 45 minutes and cycling the clutch a few times got it done well. I think you have air still in the system which is why you are not getting good efficiency.

Are you using a venturi style vac or a true vac pump???

[wheelsup]

Venturi style. I cranked the output pressure up to 120-130 psi. Brought it down to roughly 29". Not great but not bad. I know a true vacuum pump is better. However when I did it, I pulled it down and closed the service port. Rose rapidly from 29". This either indicates moisture still in system or a leak. Did it again. Increase was slower. Again. Slower still. Again. Rock steady at 29". Did that a whole bunch more times and I think all moisture is out of the system. Either way MUCH better than what I was doing in the past, just shooting 134a in there.

[JDS60R]

The reason you saw it rise was not necessarily a leak. It is pulling through the compressor so you created a vacuum on the low side and then the air from the high side is pulling out of the pump. You need to cycle the pump a few times to get the remaining air to the vacuum. Or pull from both sides.

When you turn the psi output up to 125 it doesn't stay there with a venturi style. Anything under 90 psi and the venturi style is barely efficient. You need to be isolating the ac system from the venture when the psi is lower than 90 and give the compressor a chance to cycle up to 125 again. Then connect and draw vacuum till 90 psi then isolate and repeat.

[JDS60R]

One you have a steady 29 in Hg ( almost perfect vacuum) cycle the compressor and see what happens to your readings. If they stay 29 great. If they drop - you still have air in system or a leak. Remember to disconnect the coupler before charging to assure the valve is not leaking. You will hear a hiss from it.

The reconnect, pull vacuum with closed ac bottle attached, then charge.