I just replaced the condenser which had a slow leak for a couple of years. Replaced the dryer and orfice tube while i was at it. I retrofitted it about 10 years ago to 134 and up until a couple years ago it has worked great. It had a slow leak but I'd add about a half a can every season and kept cool all summer. Replaced the condenser yesterday and pulled a vacuum but only down to -26 after an hour. I assumed is because my vac pump hadn't been serviced or used in about 4 years. It held at -26 for 4 hours so i recharged it with fresh 134. It was about 75° when i did it and I'm getting about 55 on the low side and 110 on the high side at idle. At 1500 rpm it goes to about 40 on the low and 150 on the high side. With the engine off and after sitting it evens out at about 90 on the low and 100 on the high side. I don't believe there's any restriction and the orfice tube is new. I was hoping it wasn't a bad compressor but was looking for any input from here before i blow the cash for a new compressor.

Thanks In advance

 

With a location of South Texas, I assume your elevation is at most a few hundred feet above sea level, not way up in mountains. So evacuating to only 26 inches of Mercury is a pretty crappy vacuum!

So if we go with a 30" measured, as a perfect vacuum for your elevation, your actual of 26" is 4" shy. Then take 4 divided by 30 and figure percent, = ~13%, so right off the bat you would have 13% by volume of air in your system. Air is a non-condensible, so the air will not follow the refrigeration cycle.

And that 13% air may be too conservative, as sometimes people do things like not purging their 6 foot long charging hose of air, so a slug of air the whole length of the charging hose goes in when they charge.

Then there's the folks who seal up the whole system, evacuate it down nicely for quite a while, shut off vac pump, system holds vacuum great... and then they disconnect the gauge set, and then charge it some other day, without any additional pump-down. So when they attach their high and low side hoses to charge, if they don't purge those hoses first too, the air in them also goes into the system vacuum!

I suggest changing the oil in your vac pump, and hook it up to your gauge set, and open up the manifold LO-side side wheel and see what kind of vacuum you can get as a test. May have to put the LO-side coupler onto a loose dead-headed Lo-side service port fitting to do it.

I have a question for you: When you converted your R-12 system to R-134a years ago, did you replace the original condenser with a later R-134a-designed condenser? We haven't had much luck with straight conversions around this part of Texas. At speed, cooled fine. At idle or low speed in traffic, was too warm. Limiting factor was the condenser, the designed for R-12 condenser just didn't have enough heat exchange area for 134a. Wondering what you found.

 

Thanks for the reply. I'm from South Texas but should have clarified that I'm currently stationed in NM at about 4500 feet elevation. I changed out only the evaporator, compressor, dryer, orfice tube, and the hoses back in 09. At that time i was able to vacuum down to 29 even at this elevation. I did purge the service hose before re charging the system to eliminate as much air as possible.

The condenser was never changed only flushed as best i could. As in your experience, cooling was good while moving but not very good at a stop. The new condenser is the same serpentine design so not sure if it will be any more efficient but i was thinking of adding an electric fan to help cool the condenser. I'm gonna change the oil on my vac pump an re evacuate the system before i order a new compressor. Any further input is greatly appreciated.

 

Try carefully wrapping some tephlon tape on you hose fittings and see if that helps you draw more vacuum. The seals get hard and mared over time.