First off, big thanks to Bill Curlee. I've already got him knee deep in this issue and I thought I'd get the whole team involved.

A/C was low on 134 (indicated by the compressor cycling) so I took it in for a flush and recharge. Came away with a good working system. Blowing very cold. Two days later it dies again, blows warm. Charge is still right on spec. 50 relative humidity, 70 degs, 2k RPMS it reads 30L/160H. No leaks, no signs of dye.

Facts up to this point:
- When it was cold, both sides matched so I don't think there's a vent door issue
- No, I repeat, no DTC codes. None for HVAC, none for anything else
- Fans come on according to schedule (as I've researched) that is, w/AC on, fans come on low at 185 and high in the mid 190's w/o AC on, no fans until into the 220's
- Compressor is spinning freely and does not cycle (remains on when selected)
- No lines are getting cold. The line just past the orifice tube should be ice cold and sweaty, its not.
- I replaced the orifice tube and drier today to see if it might be moisture, refilled to spec and no change.

Hopefully there's someone out that this is NOT scratching their head in confusion. Obviously, I think the "easy" answer would be the compressor, but its making the appropriate pressures........?

Thanks in advance guys.

 

not on a corvette but I had a 05 mercury sable.ac worked great for 8 years then the ac would blow cold one day next day would blow quite warm compressor running good pressures cold suction line and sweating.went to my local mechanic he said the rod on the vent door was steel and most likely rusted so the door would stick on and off.traded the car in.dont know if this helps.

 

Thanks for the input! However, I do not think this is a vent door issue due to the fact that it will cycle from hot to "less than hot" smoothly when I change the internal temp. Does not seem to be any issue. Passenger side goes hot to "less hot" smoothly as well. Plus the fact that its not pushing codes for bad door indexing.

Right now I'm focused on why that ac line is not getting cold. That is the key, I think.....

Oh, and I should've added that there were no signs of damage when I removed the orifice filter. No metal shards or anything else to speak of. Appeared clean.

 

Blows warm at start up... or gets warm after running a while?

 

Are you sure the condenser is clean? The refrigerant has to be a liquid when it gets to the orifice tube to create a flash gas as it passes thru the orifice tube. If you have hot gas at the orifice tube you will have no cooling even if you have some droplets of liquid present it won't create the flash gas. What is the temperature difference between the inlet and the outlet of the condenser? There has to be a difference or the gas cannot change back to a liquid, should be at least 20 to 30 degrees.

 

It starts warm and stays warm. Regardless of engine temp, time of day, etc. The condenser "looks" pretty clean but I'm considering replacing that next. Could it be clogged and still creating the differential pressure?

 

Here is a link on the Condenser and the tube size you might find interesting.

https://www.corvetteforum.com/forums...-a-c-info.html

 

If I understand correctly, the compressor is running all the time, yes?

If so, have you hooked up pressure gauges? It is possible that the compressor has failed internally and is not creating any pressure. No pressure, no cooling.

 

It could look clean, but you have to have plenty of air to change the hot gas back to a liquid. I use Castrol purple power mixed 25/75 for dirt and 50/50 for grease. Mix some up and spray the condenser and radiator and give it a chance to work but do not let it dry, then rinse it out with plenty of water. You will be amazed how much crap comes out.

You really need to take a temperature reading on the inlet and outlet with a thermometer and know what's going on before replacing any more parts. The line going from the compressor to the condenser should be so hot that you can't hold your hand on it, not just warm. How long did you leave it on the vacuum pump after you replaced the orifice tube? Did weigh in the charge or just guess?

 

I'll clean it out this weekend. So how EXACTLY should I measure the temps prior to and after the condenser, should I just touch the thermometer to the pipe? I'm not sure the condenser is the issue ONLY because the failure seemed to be abrupt. It was literally working when I went to work and then not working when I got out of work. But at this point Im trying everything prior to the compressor swap. The pressure read out after the orifice and drier swap was within spec. The amount of 134 put in was 1.75 lbs.

 

The fact that I AM getting pressure is why I'm confused on this issue. No pressure equal no compressor, got it. But I am making the appropriate pressure. How can I be making the pressure differential and NOT be making cold.....? Like I said in the lead in, none of the lines are cold/sweaty.

 

I use a infrared thermometer or a digital K type. The temp of the pipe is what you're looking for. The job of the compressor is to increase the pressure and temperature to a super heated gas, then the condenser with air blowing over it reduces the temperature enough to change the refrigerant back to a high pressure warm liquid.

 

If the compressor is working properly and the charge in the system is correct, there are only two possibilities I can think of:

Somewhere on the high pressure side (between compressor and orifice tube) there is either partial or complete blockage. If it is partial blockage, you effectively have an orifice tube upstream of the real one and there SHOULD be a significant temp drop at that location. If it is complete blockage, I would think the high pressure switch would shut it down, but maybe not if the switch is bad.

Either way, you are not getting latent heat of evaporation at the evaporator which is why the system is not cooling the air in the car.

Please let us know what you find...

 

Lets start with how the system works. The SUCTION SIDE of the compressor, receives the cold GAS out of the evaporator and the compressor compresses it into a hot high pressure GAS. The Condenser cools that HOT gas down to a warm higher pressure liquid. The ORFICE Tube meters and sprays that high pressure liquid into the EVAPORATOR where the liquid flashes to a gas and gets very cold.

IF the pressures are correct, the liquid that comes out of the orifice should cool the entire length of the evaporator and exit the evaporator as a gas.

NOTE! The compressor can NOT pump a liquid or should I say, it wont be happy if it does.

If you have correct pressures on properly operating gages,, it should cool.

Things to check. Is the EVAPORATOR fins or the CONDENSOR fins clogged and cant pass air to transfer heat/cold??

Bill

 

Bill is, of course, correct - I meant to say "condenser" and not "compressor" when saying that you may have a partial or complete blockage upstream of the orifice tube. Bill is also correct that if the pressures, both high side and low side, are in spec the system should cool (assuming air can pass through the condenser and the evaporator, which is exactly where Bill was headed).

It may help if you post up the exact high side and low side pressures you are getting.

 

he did. 160 on the high side is too low in my opinion. i just replaced the compressor, accumulator and orifice tube in mine last week. at 2000 rpms, 35L/225H on mine and blows ice cold.

being at 30L it might be freezing up the evaporator.

 

Blows warm at start up... or gets warm after running a while?

That's why I asked this question...wouldn't it blow at least cool for a little while before freezing off?

 

Hey guys, Thanks for the inputs. I'll fire it up today and get some pics to assist in narrowing down the possibilities. Thanks for everything thus far.


Bill, glad to see you found this thread!

 

If the evaporator is freezing up, your fan sound and air flow sounds will be a lot different and the air flow out of the vents will be a lot less.

With the AC OFF the air flow will get better as the ice melts off the cooling coils/fins.

Bill

 

Yup and if the conditions are right you might see a vapor coming from the vents... isn't this usually caused by a slight over charge?