1990 C4 Base Model, Automatic

AC is not working

Troubleshooting done and results: I need a fix

Checked for a code at the controller and got a -09 (Needs Freon)

Pulled the CTSY fuse, and after 15 minutes, I replaced it (15A - Blue in color)

Started the engine, green light is not flashing, and adjusted the temperature to 60 Degrees, and the fan at #10

I hear the compressor cycling as I rush to add freon.

The compressor cycles four times each time, then it stops cycling.

Interesting development: The system does not take anymore freon.

I filled the system with 134a. 134a fittings are on the car, I contacted the previous owner, and he did not do anything with the AC, so he was not able to tell me if it had been converted, or not. I presumed that it was converted due to having 134a fittings.

I let all of the freon out and start over. The same thing happens each time. Take the fuse out, replace it, start engine, set temperature and fan speed, the compressor cycles four times, and stops.

Does anyone have a fix? Thanks

 

When you say take the freon out...do you have a vacuum pump and ac machine or are you just letting the freon escape? If you don't evacuate the system with a vacuum pump it will not work. Also, you need to figure out how much oil is in the system. You may need to do a deep vacuum cycle to pull all the oil out and then add the appropriate amount.

 

Yes, when I originally purchased the car and learned that the AC did not work, my Buddy from Dallas who has vacuum equipment came down and pulled vacuum after removing the very little freon that was in the system. Since then, nothing that I have done has gotten the AC working. I need a member in Houston Texas to give me some time and educate me on this issue.

So, I am on this long journey and am too proud to take it to a reputable service shop.

 

You need the compressor running to add freon. Try and jump the low pressure switch to keep the compressor on while you add the freon. After you get a sufficient amount in there, you can reconnect the compressor and proceed to finish the job.

 

I would say it is most likely the pressure sensor switch then.

 

Okay, since the compressor cycles when I take out and re-install the CTSY fuse, I will re-install it and disconnect the pressure switch before starting the engine. Then, I will jump the pressure switch wires to get the compressor running as I fill with 134a.

Question: Is the orifice in the drier line? I want to change it out when I have the system evacuated. I want to know where the orifice is, and replace it.

I plan to get the 134a removed and vacuum the system out again, thus starting over with a dry/empty system. I want to re-affirm that it is holding a vacuum, new orifice, no leaks, then start fresh.

Well, that is how I am thinking about it.

 

I can never keep straight which side is high or low. The orifice tube is easy to find. It will be in the pipe that has a connection right out in the open with 3" of straight pipe behind it.

 

Acknowledged about the location of the orifice. I have changed these things out before on other cars, but never the Corvette. I will take it from here and make my repair. Thanks for the quick response.

 

Acknowledged. ihatebarkingdogs,

I printed your instructions and will follow as soon as I get a chance, this week. Thanks

Currently, system is empty, new orifice.

I learned about the reset procedure, and it made since after a couple of times the compressor cycles four times and quits each time, When I take the 15amp fuse out (CTSY) for 15 seconds and replace it, I can get the compressor to cycle again, each time, four compressor cycles and compressor stops.

I will follow your instructions, with the exception of heating the cans. I do not have a means of doing this. I plan to allow them to sit in the sun prior to my work to get them warm at least.

Thanks, again. Your explanation is new, and detail enough that I should have a successful repait. I will cirlce back after I have completed your instruction and let the Forum know of the outcome.

 

Solution:

Just to change it out, I changed out the orifice tube.

I reset the compressor by removing and reinstalling the CTSY fuse. When the A/C is turned all of the way down and the fan speed turned all of the way up, and the engine starts with the A/C controls to 'On', the compressor cycles 4 or 5 times.

Be prepared to add freon (R134A). It is a good idea to do a vacuum and make sure that it holds to affirm no leaks in the line. Add freon while the compressor is cycling, and it will catch, thus keep running and begin cooling the cabin. Use your gauges to get the correct amount into the system. Your problem is likely solved, if your switches are good.

The key is to rest the compressor each time that it cycles out.

 

The correct answer was in post #4.
jumper the low side pressure switch connector to run the compressor continuously during the refill. Turn the A/C to high and the blower to high. roll down the windows. You don't want to ice up the evaporator core or the readings will be off.
Also on a system of unknown history you want to replace the drier (they are inexpensive) and refill the system with the correct amount of the correct oil. On old cars I just go ahead and replace the O-rings and Schrader valves while I'm in there.
Pull a hard vacuum for 30+ minutes. This isn't a leak check, it's to remove any air and moisture. I
If the system doesn't already have dye in it now is a good time to add it.
Use a A/C gauge set or you will not know if the system is actually full and how well the compressor is working. These are also inexpensive and a complete set comes with a vacuum pump. If you are never going to be doing A/C work again you can rent a gauge set and pump at many car part stores. Just be sure to flush out the hoses with Freon prior to connecting the lines to the car or you will be introducing air. Bad mojo.
I put the cans in a bucket of HOT water while filling the system. just keep the can upright so you are pulling vapor not liquid. Even from the little cans a fill goes quickly this way.

 

Another example of wrong information so rampant on this site. A refrigeration vacuum pump will not pull liquids - oil, water, or cat ****. A vacuum pump has two main purposes. One - to remove non condensables such as nitrogen and two - to lower the pressure inside the system in order to allow moisture to boil off and turn to a gaseous state so it can be removed by the pump. Many like to put in their two cents but really know nothing about refrigeration. We recently had a thread here where the dude was trying to vacuum so low that the lines were in danger of turning inside out. The industry standard is 500 microns. At 500 microns, water boils at -12 F. Unless you are trying to vacuum a system outside in a blizzard, how much lower do you think is needed?

 

I have a Robinair 17800. When I pull a light vacuum there is very little oil removed. When I do a deep pull around 30 minutes it will have an once or more. This comes from the oil separator on the side of the machine. Robinair's instruction manual goes over the importance of verifying it is empty before you start and checking it before you finish to replace the exact amount of oil pulled during the recovery/evacuation process.
I previously only used a straight vacuum pump. It had a steam port. While it was pulling, steam always came out. I was always uncomfortable using that as I don't know for sure what was making up that steam. My dad always said that was just the humidity in the air that is in the system turning to steam. Always seemed like a lot of steam for so little air and it kept going even after a vacuum was pulled. So regardless of what know it all's say, I believe a vacuum pump does pull oil. Maybe not all, but enough that Robinair added an oil separator and wrote a procedure on it.

 

A common myth. The max pressure differential you can get at sea level is around 14.7 PSI not really enough to turn the system inside out. The differential between 500 microns and pure vacuum is only around 0.01 PSI at standard conditions so if an additional 0.01 PSI turns the lines inside out you had a bigger problem.
As you know it's not just the depth of vacuum but also the duration to boil out any aromatics.

 

Seriously dude? You don't recognize sarcasm when you see it?🤣🤣 Back to your books!

 

Do some research. First of all, your father was correct. Secondly, any oil separated is coming from the refrigerant.(read the directions, it tells you so - "This oil was removed from the A/C system during recovery." It then tells you to go on to repairs. Generally, repairs are made before vacuum. The recovery process is relatively short compared to the vacuuming. Your statement said that a deep vacuum was needed to recover ALL the oil. False.

 

My bad. now corrected.
I've never used POE. Just done a through flush and replaced all o-rings and seals with PAG compatible and used a correct viscosity PAG oil. I figure at some point a tech or owner is going to put PAG in there anyway. I also didn't like the chemical instability of POE.

 

Experiments can be enlightening. There is a guy by the name of Bryan Orr. He is the owner of a large HVAC company in Orlando. He also owns HVACRschools.com. Both very reliable sources of information. He publishes numerous articles in various refrigeration publications. He states that despite extensive research, there is no evidence to oil being removed by vacuum. During recovery of refrigerant yes - because this oil is miscible(mixes with the refrigerant) Hence the oil separator on recovery machines. However, as I previously stated, the recovery process is relatively short compared to the vacuum down. If the system is very moisture laiden, then yes, there will be a lot of "steam". Most refrigeration oils are hygroscopic and removing the moisture can be difficult. There are several videos on Youtube showing these attempts with various oils. POE seems to be the most difficult. In a very polluted system, breaking with nitrogen a few times may be necessary as the moisture may freeze under prolonged vacuum and need to be warmed.

 

It took me quite a while too to wrap my head around this. Thermodynamics can be confusing. I'll try. When the pressure is lowered, water boils at a lower temperature. Same as climbing a mountain and boiling water for use. However, heat is still required to make the phase change from liquid to gas. This heat has to come from some place - the surrounding area. The available heat is used up and the water freezes. Same as frost accumulating on a propane tank when it is being heavily used. The pressure inside is dropping and the liquid propane is rapidly boiling. Once again, the heat has to come from someplace - the tank. There are also videos demonstrating this. That is my understanding. An egghead may correct me.

 

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