Guys! Im sweltering down here in Dallas and am working on my '70 mustang a/c. Everything is original, charged with r-12. Compressor makes the growling noise and sucks power from the engine but the air blowing inside is just barely cool. I had a guy show me that if I unwrap the expansion valve and loosen the fasteners holding that bulb and pull it free from the evaporator tube, it blows super cool! so what does this mean? Is the expansion valve bad or some other component? What does that bulb at the end of that flexible tube on the expansion valve do anyway? I'm scratching my head here....
the blub on the end contains a charge that makes the valve operate,
when you take it loose, it tells the tx the superheat is calling for it to open more.what refrig you have in the system is flowing with no restriction.
with the engine running and a/c calling,check the sightglass on the receiver /drier and see where your refrig level is.you will poss. see bubbles which mean low on charge.
the noisy comp might be a sign of bearing /seal failure.which could be wear your leak is,
I'm think what you're talking about is called a capillary tube and it's basically a temperature probe that most times, is ran directly into the evaporator core (between the fins) and sences when the core is about to freeze up, and cuts the power to the ac clutch. Which keeps the evaporator form freezing up and turning into a block of ice. Now as for unwraping it causing it to work. I'm not sure exactly what the heck you've got going on there??? I don't have a lot of experience with older car a/c systems, as I couldn't afford one back then with a/c, and besides that, it sucked horsepower! JTS 71 Mach1
Ok, thanks! So i checked the sight glass and the refrigerant is flowing with no bubbles. So I understand better what the bulb does, but still not sure about what I need to do next. I can disconnect the bulb from the mounting point on the evaporator tube and have it blow super cold inside the car but I'm afraid I will wreck something. Since it blows so cold when I do that I figure the compressor and other components must be working well. So I'm still wondering if my expansion valve is bad? Just seems strange when the bulb is against the evaporator tube just barely cool air blows inside the car with the compressor running. Still scratching my head...
the tx valve with the bulb on it is a metering device that lets a set amount of liquid refrig. into the evap.as the liquid goes in it boils off
and becomes a vapor that the compressor brings back.the bulb regulates this amount by superheat from the evap.
with the bulb unattached it will let more liq.through and if to much, will flood back and take out the comp.(it only pumps vapor not liq.)
the cap tube that is in the evap is the stat.
on comm.systems the bulb can lose its charge and not opening the right amount will give a warm case.by loosing the bulb we can get more through until replaced.
I have been doing this for 35 years,cars can be diff.put the equip operates the same.
Ok great! You have taught me a lot about these a/c systems. I'm thinking and you seem to be suggesting that the bulb on my expansion valve might be suspect. I'm going to change it out since they are not very expensive and see if that changes things. We have been dealing with a run of 105 plus temps down here and with my boys home from school I have to make my '70 mustang my daily driver. It's been tough!
Thanks again!
hope you know that the system needs to be recovered and the gas is high pressure, you just dont take it off.
if you have access to a gage set, get reading first before condeming the valve,at those temps the high side is going to be so high that what you are getting might be all you get until it cools down.
Good Job 68machowner as I told him I didn't have much experience with the old systems. When you described the TX valve as you called it, I remembered they used to have variable expansion valves (as I would have called it). They phased most of the variable expansion valves out in the late 80's early 90's as I remember. Now most everything now has a fixed expansion valve or orfice tube. Which usually works good until it gets plugged up. Good info. JTS 71 Mach1
sorry guys, I hope I didn't come across to strong,but I have seen people get hurt with this stuff and didn't want it to happen here.
there is alot on these old cars we can do but the A/C is a field to its own ,one false move and just the cost of replacement 12 is only minor compared to frozen eyeballs and loss of body parts.
I enjoy the way everyone here interact compared to other car sites.
Bob
Yeah Bob, you said a mouthful. I have never seen this kind of care, and commaradery before. And just like this question. We have several different answers, each one adding their expertise, and helping us all do a better and safer job on these old cars, as God knows there are a lot of ways to get hurt. I want to say thanks to everybody on this site, Because "together" there is no problem we can't resolve. Thanks to all, Guys.
JTS 71 Mach1