My '72 has been lingering along with the stock condenser up front since birth.....it is so corroded and bent up, I decided to replace it....BUT the only affordable condenser I found that would take this 134 is the one of similar size from Vintage Air....so the royal PIA was the plumbing, largest one was the pipe from the stock cond. to the receiver/dryer I had to cut off that aluminum pipe, and fashion up a top pipe also...I managed to adapt it all inline, and so on chilly day say 55f outside, it managed to stay at ~25" vac for several hours....and so went to pressure the thing....stayed at ~50 psi for a LONG time, then I fired it up and ran it and put in another can of 134......

here is the trick, the discharge of the valve into the evaporator tends to freeze up....not really grossly, just frost over, and the output from the cond...that large loop over the top is fine at the evap end, but at the input to the comp, it tended to frost over....

the comp is a serp drive unit from a '88-91 vette....all the valves and crap had been changed some years ago.....

since it is chilly weather and higher humidity...what do you all experienced A/C techs think of my symptoms,?? the air flow into the car seems fine, and a ~20f drop....the car is in constant recirculation, being a convertible...

maybe the ambient temps too chilly to allow a full load of 134??

 

Try autoacforum.com. Those guys are the best, even on our older cars.

 

Please let us know the solution!

 

mrvette - not sure what you are asking(?), but when I started looking for the biggest condenser I could squish in I saw multiple different sizes on Amazon. I'm still pondering, but if that's what you're asking about, then you may want to look there.

 

I know this and can say this...is that IF an A/C system was an R-12 system and it wanted 2 pounds of R-12 Freon in it....you do not put the same amount of 134A Freon in it...it takes about 70-75% of what WAS required....and you want to watch your high side pressure while doing so....or at least.,..the guy who does all of my A/C works does it that way and I am standing there watching him do it.

AND...on some cars...that have electric fans....many times it requires BOTH cooling fans on when the car is sitting still due to no air being pushed across the condenser like it would be if you were driving. I have personally seen the high side pressure change when an the second electric fan is activated and not activated.

I do not know if that helps...but I also know that frosting up can be attributed to current weather conditions.

DUB

 

Specs for my ‘69 AC calls for 4+ lbs of Freon.

 

Do you have a set of service gauges that you can give us the pressures while its running?

What type condenser did you get, parallel flow or tube and fin?

With the cooler weather and depending on the charge condition you can experience what your seeing.

Neal

 

That's what I thought guys, so to put off for a HOT day...say 80f+ ambient and in the sunlight....probably be near April, even here in north Florida....

I think it's parallel flow, and I don't have high side gauge, just lo side....reading ~30-40 lbs....

 

Frosted valve at evaporator is either low side restriction or an extreme amount of moisture in the system.

 

If i understand your description correctly the frost on the lines is simply an indication that the temp of the lines are below 32* F and causing the condensate to freeze at the pressure drop point and downstream of the evaporator coil (outlet line to compressor). This can be normal as the coil temp is below 32* and the ambient temp is cool enough that the system is not picking up enough heat from the cabin to bring the temps of the coil up above freezing so your seeing the frost at the compressor.

Charging an Automotive AC system can be tricky with the ambient temp your seeing,

knowing the high side pressure is critical to determining if there is an issue with the system but from what you are seeing it doesn't appear that there is.

I think your on the right road, wait until it warms a bit and take another look,

Of coarse not being there to put my hands on the AC its hard to diagnose over the Internet and if these symptoms were happening on a hot day I would be a little more concerned.

Neal

 

It's along about 1pm now, sunny in the driveway, and engine is warmed up....I going out in a little while to see what is......

trick is, I see a replacement for 134 system, involving the long skinny valve with the lo side port on it, and the replacement has a pressure switch and wiring harness to interrupt the compressor if it's not right, hate doing that, have jumpered out SO many of them switches over the years, why introduce a problem when the system SEEMED to be working right, and all I wanted to do was clean up the airflow to the new radiator/trans cooler, and maybe improve the operation a tad by using a cond. for 134 instead of the 12 from '72.....

 

That is R-12 Freon...BUT if 134a is used...you DO NOT put 4 lbs of 134a in the system. Just to clarify.

Waiting until it warms up may be a wise move. Its has been 40 degrees F in the moorings here and I still have people wanting their A/C fixed. I think they should be more concerned about the heater core being in good condition and functioning.

I will 'say'....You can do as you wish...but 'those switches' are there for a reason. Bypassing them is your choice....but that kinda falls in the same mentality that you take out a fuse that keeps blowing and put a nail in its place. Possibly asking for other problems that are greater than fixing the initial problem. You must not have ever been standing by a car when the high side pressure goes off the charts and the system blows out the Freon because the pressure switch was bypassed. And the Freon is not such a big deal but it is all of the oil coming out also.

DUB

 

I dunno why, but never had any issues by doing that....and this afternoon at ~70f outside, the pressure was fine and the cooling was fine with NO evidence of freon loss.....so on to the heater core plumbing hose crimp problem.....minor problem, and plenty of heat now...., so over the 'winter' will look to reinstall the overflow tank on the rad..... yawn......

 

I may be misunderstanding what you are saying, but, if the pressure switch causes the A6 compressor to go into a cycling mode, it causes problems because the clutch is not robust enough to handle cycling. GM designed it to run continuously. The next generation compressor was designed for cycling.

 

I have a serp drive from '88-91 corvette, so the comp is a new style....I get confused on the makers, Sanden, Sankyo, etc??? at any rate, it may be designed to cycle, on/off.....but that just seems like a rather silly way to do things, like the lack of a metering valve .....long ago, I forgot to mention, I pulled this long skinny valve, and adjusted a nut on the top/inside of it, like 1/2 a turn? counter clockwise...and it pulled the valve setting in line with rest of the system....

I suppose it's just such a hotrod system at this point, I will have to set back and play with it until it settles down....

 

Sounds like you adjusted the POA valve.

 

By 77 all GM cars had transitioned to CCOT, the Frigidaire A-6 was used well into the early to mid 80's in GM vehicles along with many other manufactures. The clutch was well equipped to handle the cycling.

Neal