Automotive Air Conditioning Information Forum

Ok folks. Updates.

So I think my spraying the garden hose on the condenser kind of messed things up a bit by making pressures seem lower than they actually are in real-world use. So this morning I checked things out, avoiding any kind of garden hose manipulation.

I did not add any more refrigerant, yet.

Today it was quite humid. Rain later today. 85F ambient, and 70% humid.

I think I am getting about 31F subcool, unless my calculations are off. This time I took off my front grill so I could get my infrared thermometer closer to the condenser outlet.



On measuring the low pressure side, there was some difficulty there. I first attempted to measure on the the service port fitting, but was getting a super hot reading there, 140F. But when I measured the #10 hose fitting at the evap, I was getting 85F. Keep in mind this is an old school van with a very cramped engine bay, so there's a lot of heat in there.

If I used the evap fitting temp reading, I calculate 38F of superheat.

Please check out my updated table below:

We need Detroit to weigh back in, but I have some thoughts.
Your superheat cannot be 93, else you would have no cooling at all. I would disregard that 140° reading. The true superheat will be thrown off because your temp and pressure are not being taken at the same place, and your suction line is long. I understand your limitations.

While you have the grill off, why not also get the temp of the pipe into the evap at the same time as the pipe out, especially since you say there is so much underhood heat

We assume all your readings are at 1500 RPM, max cool, max fan, recirc, doors open.

Yeah, I was thinking of disregarding that 140* temp and just going off the temp I get at the evap unit.

I can get that other reading too once I go back out and take another stab at it.

Yep, all readings are at 1400-1500 rpm, max cool, max fan, recirc, doors open.

Good. Get both pipes at the same time and note ambient

Nice job, we are getting a clear picture of what's going on.

31F subcool, you are overcharged a bit, HS pressure of 240 psig still quite reasonable. The overcharge isn't hurting you very much.

85F at the evap outlet fitting is really your problem. TXV is way out of adjustment, it's killing your performance. No choice but to adjust the TXV bias screw to get less superheat. As you go through the process of; crank the screw CCW, evac, recharge, the evap will contain more refrigerant liquid while running, so it might be that your current charge level is close to correct. Hopefully you took careful notes on how much was charged, you can just recover, adjust, charge to the same level.

Your TXV is so far out, personally I'd give it a full turn CCW, just my guess. I keep calling it a screw, but for your valve it's probably more like a brass setscrew, open center, hexagon on the inside.

Wow! This is exciting.

Not ideal but glad I'm feeling like I will have a solution.

So I will get the refrigerant taken out, then remove and adjust the TXV. Then start all over again. What if it's still not right? I have todo it all again right? That's a lot of money spent on r-134a, haha. But it is what it is, I suppose.

And just confirming I shouldn't replace my TXV? What if the sensing bulb has no refrigerant in it? Thank you

Yeah, I forgot you have a sensing bulb. How is the bulb installed and insulated? Has to be in good thermal contact with the pipe, well insulated with black goopy stuff so it measures pipe wall temperature and not the temperature of water condensing on it or the surroundings.

If the bulb or capillary breaks and the charge escapes, TXV will be tight closed, suction pressure will immediately go into vacuum, no cooling at all. That's not what you have

It’s on the pipe, but kind of loosely insulated. You can see the photo of it on an earlier page.

But doesn’t it flow more if it feels hot? So not being smack dab up to the cold pipe and without proper insulation would lead to more flow, not less which is my problem. Is my logic correct?

That pic is very crowded. Cannot tell what it shows. There should be a metallic clip or clamp holding the bulb to the outlet tube, and the bulb should not be on the bottom of the tube. Then there should be your insulation which looks like the gooey cork stuff called presstite.

Your concept of function is correct, but regardless of all the above, improper adjustment of the screw Detroit talks about can limit the overall function. In a sense it is a governor, such as might be found on a big truck to limit carburetor function to limit top speed.

Think of a lawn sprinkler system where you have only opened the main water valve 1/2 way

On residential and commercial applications the adjustment screw on the TXV can be accessed externally. If only auto AC were like this

I have no idea of the language being spoken here, but the guy is removing the adjustment screw completely.
Of course that is not your goal. You would want to turn the screw CCW as directed by Detroit
go to 4:00, the earlier stuff is of no matter
https://www.youtube.com/watch?v=ZgVrbtO6i-g

You are correct, poorly insulated = warmer bulb = more flow

Like many things in life too much flow is bad, too little flow is bad, there is an optimum.

I just mentioned that bulb because it looks tight in your picture, hard to tell how well it's mounted and insulated. You don't want to be chasing your own tail trying to adjust a TXV that can't sense suction temperature.