45 psi is too high for the low side. If he has the R4 compressor, then it's supposed to cycle. If it's the A6 then it should not cycle, either way that low side reading is too high. R134a doesn't cool as good as R12, but he should see at least a 30 degree difference from ambient. Which he is not. Also, if it is the R4, then capacity is 2.5 lbs for r12, and 80% of that for r134a. The system might be overcharged.

 

I do have the R4 compressor

I have observed the compressor cycle only when the Freon is too low at first (when I first added the Freon) and when the electric fans I had were off. And the pressures got high. However during the normal tests of the system I keep those fans on constantly. So I would assume both low and high pressure switches work correctly.

Im working on getting a new drier, orifice tube (blue), and a flush kit so I can restart and get all the oil out of the system. Then I can add the right amount of oil in.

 

That is probably the best plan.
Most of your oil should be in the filter dryer and the compressor. You might want to just take the compressor back off and pump/dump the oil out. Then flush the evaporator and condenser and associated lines, then flush the compressor while it's off, blow it all out with compressed air really good. It's a bit of a nasty job, wear a respirator.
Put some oil in the compressor and the rest in the filter/drier. Rotate the compressor by hand to get the oil moving into the lines once you re-install it.
I think I would still use ester oil vs PAG for this unless you change everything out. There will be some residual mineral oil in the lines or condenser/evaporator you cannot get out.

I've been using ester oil in my AC for over 15 years now in my 77 with a blue orifice tube and R4 compressor and it works good.

Remember to purge the charge line of air each time you install another can if you are going to be using the small charge cans. Even a small amount of air affects the duct temps. With that air comes moisture, how much depends on your humidity on the day you're doing it.

 

The hissing noise is fairly normal especially on a hot day, greater DP across the orifice.

what are the conditions of the car when you are testing/charging the AC? Parked in the shade, doors closed, windows up, fan on high, AC set to MAX?
Line at the orifice should be around 26 to 30* and evaporator outlet should be 36 to 45* or in that area which will cause the suction line to sweat back to the compressor if its charged correctly.
May need to validate the recirculation door is closing or it will be very hard to get air temps much cooler than what your seeing with the fan on high
Our AC systems are not optimized for 134a (parallel flow condenser) but should easily maintain a coil temp of 30* allowing for adequate cooling
134a was formulated as an r12 replacement and is slightly more efficient then r12, the pressure/temperature relationship is very close at pressure of 28 psi which translates to a coil temp within 2* of each other at the evaporator with the same size orifice. For me I'm not sure the effort is worth the gain to change the orifice.
I agree when a conversion from r12 to 134a is done then ester oil should be used, never PAG unless the system is cleaned of any mineral oil.
Its very hard to look at just the suction pressure and say the charge is good but you have talked about other indicators that lend some insight into your AC, along with pressure there is the suction line cold and sweating, and the charge volume is close to the needed amount. In our cars with a conversion and a sub par condenser I would expect to see high side pressures in the 250 to 280 psi range and low side pressures in the area of 40 to 50 psi.
You've commented that prior to the compressor change out the AC cooled a good bit better so something is a miss and needs to be corrected.

keep us posted on what you find,

Neal

 

Just wanted to verify 6 oz oil (For ester? Or are both oils the same quantity?) for the complete system with the R4 compressor? I guess I could do ester oil, but being that the compressor calls for PAG 150 I'd kind of hate to go against it. Hopefully with the flush I can get basically all of the oil out. I've also heard of splitting up the oil, like 3 oz in compressor, 3 oz in the condenser, not sure how much that matters.

Conditions vary, but I keep the car under shade with dual electric fans running and the rpms higher than idle (1000 rpm ish). Max fan/reculate, doors closed. The temps I've given are after the car has done it's best to recirculate and cool the interior, often temps out the vents at first are higher and slowly cool down and eventually reach some sort of equilibrium. Based off many hours of highway/city driving, it really doesn't get any cooler driving or not, +/- 5 degrees. The electric fans move quite a lot of air. I've even driven it in the morning to mid day, in the morning the a/c can keep up, but slowly the a/c couldn't keep up once the sun really started shinning.

When feeling after the orifice before the evaporator it's cool to the touch, but very clearly not ice cold.

It does seem to be related to when I replaced the compressor, which I can blame myself for.

I'll also check on the blend and recirculate door, make sure they are working. I'll also check and clean the outside of the evaporator, being that there is no cabin air filter on these cars I'm sure there's a couple of leaves.

 

The fact that the line right after the orifice is not ice cold is a sign that something is not right, try misting some water on the condenser with a water hose and see if the temps drop both at the vents and at the orifice.
Cool/cold freon returning to the compressor is needed to lower the discharge temp and pressures going to the condenser to get the system over the hump and working correctly. I've ran across this a few times under very hot temps and high humidity conditions. By misting water over the condenser you should see the suction pressure drop and the coil temps will also drop if not there are other issues but if they do come in line then usually adding a little more freon will get it where it needs to be but if not then based on the discussions in this thread I agree that the possible issues are more than likely air in the system and possible excess oil and the wrong type of oil.
You can fix both, for the oil the system should hold around 6oz of oil with 1oz in the condenser, 1oz in the evaporator, 2oz in the accumulator/dryer and the remainder in the compressor but make sure to spin the compressor by hand 8 to 10 revolutions after mounting prior to engaging it with the engine running. Its always a good idea to drain and measure the oil from the once removed from the car so you have a good idea of how much was in there.
Removing the old oil is fairly simple, get some flush and compressed air, remove the lines best you can from the main components' of the system, shoot some flush in and follow it with air until the air comping our is clean and dry, do the lines also. for both the coils in the top and out the bottom with flush and air, for the dryer there is no easy way to clear it so replacing is the best option (absorbent bag internal)

This was mine when I pulled the coil;



Neal

 

Yep 6 oz regardless of oil type.
It calls for PAG because it assumes you are using it for a clean 134a system.
By the way, your old compressor is a better compressor than the new one. It is possible to replace the front seal on it to seal it up. I've replaced mine twice now.
New compressors....hard to say what life you'll get from them.
keep the old compressor if you still have it.

 

One other variable to look for, when vacuuming the system down your vacuum pump will be making a popping noise initially. That's air coming out. It is only clear of air once the popping stops.
if you have a leak somewhere, like a bad charge hose,, or loose connection the popping noise will not go away.
so listen for that to stop, telling you the air is purged.

 

No unfortunately I gave up that compressor for the core charge. I do have 1 or 2 other old R4 compressors off other cars, however there condition probably isn't great.

I had a real bad compressor mess with a S10 I had, went through like 3 R4 style compressors. But the compressor on the corvette currently is the quietest one I've had by far, and the clutch on it wasn't all screwed up like the other ones.

What I think I did wrong this time around is put way too much oil in the compressor when I replaced it.

 

Slightly dirty orifice tube. It is the white one, although it appears gray.

Im flushing out the system currently, but for the compressor should I spray a little cleaner in there to get the residual oil out? Or just let it be? I don’t want to damage the compressor but I’m sure there is a lot of residual oil in there. I probably got 3 oz of oil out of the compressor from just holding it over a big cup.

 

don't add flush to the compressor, just stand it on its end and drain as much of the oil out as you can and measure it to see how much oil was in it.

Neal

 

orifice tube doesn't look bad at all,

Neal

 

I guess it depends on how likely it is that PAG and mineral were mixed. If you believed that happened I would also flush the compressor. Just blow it out well rotaing it a bit and add your ester oil back in to it and rotate it again to get it well oiled.

That orifice tube is plenty dirty. I've seen worse, but how dirty does it need to be before affecting performance? Who knows.
big deal is getting the blue in there IMO.

 

I wouldn't be surprised that tube was the cooling problem. BTW, the R4 compressor is one of the worst designs ever. The rebuilds suck. The newer {looks different} design is a little better, but the only way to go is new. Just let the compressor drip empty. I would not spray flush with concerns that you won't get it all out. If there's a little oil left, it's not a concern. Besides, if you flush it, you might void the warranty. Be safe!

 

Warranty? Lol, good luck making good on that. It usually requires replacing the filter drier, using manufacturers recommended oil/procedure and using a "certified" installer. Deviate from any of those and you are on your own. If it came from a reputable supplier, like summit, you may be able to get a component replaced by them, but not the manufacturer.
Most warranties are almost as good as the paper they are written on when it comes to Chinesium parts.

 

Well, you should replace the accumulator, and using their oil recomendations. Why would you want to deviate from that logic? 90% of failures are due to installer error, and that includes "certified" installers who take liberties on installs.

 

We are not in disagreement. Like I said, that ship has sailed in this case.
In addition unless all the associated R12 components are replaced then using PAG would be a recipe for likely failure. Short of that, using ester is the best course of action.
Despite any manufacturer recommendation.

 

Okay the system has been flushed fully, added 6.25 oz of oil total to the system, spread apart through the evaporator/compressor/condenser.

Changed out the orifice to the blue orifice.

After adding the first can of r134a (12 oz each) I noticed frost forming very quickly after the orifice, which would quickly appear/disappear when the compressor cycled. Once the second/third can were added frost stopped forming entirely.



Outside it has been around 92F. Going by charts I've seen online a good charge for r134a should be 45-55 psi on the low side.

With the engine running at 1800 rpm, electric fans on. The low side shows around 35 psi. So a bit low with 34-36 oz of r134a in the system. Even though I can go add more freon to the system I really have my doubts that it will help the system cool better. Even now I'm still only getting a coldest vent temp of 63F. Lowering the engine rpm will quickly increase the vent temp to mid 70's.

I should probably go get another can and get the pressures right, but it really feels like I'm throwing money in the trash at this point.

 

Capacity is 40 oz, so you're a little low.

 

Charge it to the lowest low pressure that gives you the lowest duct temp. In other words once ypu hit maybe 45 to 50 * or so out of the duct and have maybe 45 psi you are there.
Are you absolutely sure the heater core is not adding heat to the duct temp? Do you have shut off valves on both or at least one heater core hose?



When I look at my chart it shows 46 psi on the low side pressure at 90* with 50% humidity.
Lowest pressure on the chart it 37 psi at 70* and 20% humidity. So you are a bit low on the pressure and 134a according to the pressure charts.