Thread: Any A/C experts out there?

Tweet

OK Guys, based on earlier input I went looking for my expansion valve and for restrictions in the system, and I think I may have found a restriction. On the new hose that runs from the direr to the evaporator on the high side, the 90 degree metal fitting is a smaller diameter than the old hose fitting. The old fitting was 3/8" OD, the new fitting is 5/16" OD and then steps up to 3/8" at the connection point. Is this enough of a difference to cause a problem? The high pressuer side is pushing along through a #6 hose between the drier and evaporator and now has to go through a smaller pipe than before. I think the hose maker used what he had instead of what was actually needed and I did not even notice it when I went to install it because the fitting on the end was still the right size. Thanks again for all your help.

Denny those readings look like what I am looking for with 90 degree ambient, Troy that Vintage Air trouble guide is very helpful. From that I have a restriction, a bad expansion valve or am over charged. The growl and chatter could make me think we have air in the system, but I know it has been well evacuated.

Thanks again

Pat

If you suspect a restriction in the expansion valve, check the temp of the line on either side of it. Normally the temp should be same on either side. If there is a restriction there, and you have the proper R134a level, you will see a temp difference.

Also, you never told us how much r134a you put in the system.

The dye could be a factor. We did not weigh the supply tank, only going by gauges to determine the amount. Next time we will use a scale. I will find out how much dye went in tomorrow, it was put in by the first shop that worked on it when we were chasing leaks. So the consensus is if the expansion valve was partially clogged it would not cool at all?

thanks again for all the help

Pat

It is a simple thermodynamic principle. Your a/c system is a heat mover. For the evaporator to remove heat from the vehicle, a defined amount of fluid must pass through the valve and then the evaporator. This fluid will move the heat from the vehicle and expell it.

When the a/c system "blows cold air," it is removing heat. For the system to remove heat there must be a sufficient flow through the expansion valve or orifice.

Restricted valve or orifice and no fluid flow and thus no cool air.

Thanks again everyone, I will refrain from using the A/C until this is resolved. I spoke with the folks at Southern Air, they are the ones who built the original system. He agreed there is a restriction and indicated the small fitting may be the problem. My next step is to pull the hose with the narrow fitting and have it redone with a proper one. This will have to wait a little bit as my buddy with the gauges, vacuum pump and 134a tank is going out of town for a while. While I have the system apart I will look for other restrictions and make sure everything is clear. I will also look into this stuff:

http://www.acsource.com/index.asp?Pa...OD&ProdID=1245

And may flush the system depending on how far I need to take it apart, per the instructions. We will weigh the tank as we charge, I have a fishing scale that reads in pounds and ounces, and set the target for 2 pounds or less. The Southern air folks said the pressures are the ultimate measure as the vairied size of systems makes it difficult to predict an exact weight of 134a to use.

Just like other experiences, I am sure learning a lot about auto air conditioning works and I thank all of you for taking time to share your knowledge.

Pat

Thought I should wrap this up and let you know what happened with this, thanks again for all the replies. We got the system working right last week-end. Basing our actions on the idea that there was a restriction in the system, we removed the refrigerant, then flushed the condensor and evaporator and made sure the hoses were clear. We then vacuumed it for over an hour at 28+ inches and checked to make sure it would hold the vacuum. Then we slowly applied the refrigerant, this system has always been R134, was never R12. We did not have a scale to measure how much we applied. The pressures came in just like they should and we ended up with just under 30 on the low side and 190-200 on the high side. We had to set a fan up to blow through the condensor to get the final pressures just right. It is blowing 35-36 degrees with the fan on high now. The odd noises are gone and it seems to be working like it should. We believe there may have been residual oil and/or dye in the system and flushing it has solved the problem. So Stu Cool (that's the Studebaker's name) is indeed cool as it should be!

Pat

Yeah I think the only thing I would worry about is frying the compressor. You should also add an ounce of oil to the evap and condensor.

You got such good advice on your A/C I have a question

I want to put a A/C system back in my 1977 Chevy C10 truck
It originally had A/C I would like to use R134 I have the old R12
pump but it is bad What is the best way to go about this

Ron 52

I have changed over a few of my Avanti s to r134 -you minimal have to change out receiver /dryer, o-rings completly flush system w/ cleaner to remove traces of old oil . Install new compressor w/ ester oil, charge to ~ 80% of r-12 capacity- better to go by weights. If you do not change all hoses to " barrier hose" you will have to top off ever 6-10 months as r-134 partical size is much smaller than r-12 and w higher r-134 static pressures will seep out through walls of hoses. 31 5w