Automotive Air Conditioning Information Forum

Hi All,

Long time reader, first time poster here. Until now I have always been able to find answers to my questions using the search function, but I guess this one is a little unusual...

I have an early C4 Corvette which has been converted to right hand drive as per the requirements of my country.
As a result, the evaporator is now mounted on the LHS of the firewall and the liquid line ex condenser and the return from the evap are now plumbed across the front of the motor in the path of the hot air from the radiator/fan.

I wondered if this was hurting performance. As an example, at idle on a ~80F day with the condenser fan running, the liquid line leaving the condenser is at about 86F, but after crossing the engine compartment to the evap, it picks up heat and measures about 114F just before the orifice.

Will this hurt AC performance? Is it worth insulating this line?
The high side has always been a bit higher pressure than it should be and I think this might be contributing, is this possible? - due to the extra length, but mostly the additional heat? The high side port is on the 'hot' end of this pipe, just before the orifice.

Many thanks for your expert input!!

Long story short, I would insulate that line. The system is not designed to remove that much heat. Be sure your low side line is also insulated under the hood, and I would also insulate the receiver/dryer, if not already done
We really like pressures both hi and low at idle and at 1800 RPM. It seems you are able to get pressures, so please share. Also ambient and vent temp at the same time. Your hi side must awfully high....
It sounds like your components (condenser and evap) are mounted sideways. A pic here would definitely help. If this is true I don't see how you could get any cooling at all.
A stock setup in a 'vette in the USA will still be difficult to cool the car for many reasons.
The extra length you mention is not a problem.
It would be hard to do, but I'd also insulate the firewall.

It is hard to believe they would force you to change the drive of the car. I am having trouble thinking that you could get the mirror image components required to do this.

Keep us posted we are here to assist.

Thanks for your input.
Sorry I didn't post all the numbers. I was only seeking opinions on whether there was something to be gained by insulating the liquid line in this example.
I was quite sure it would have to help as half of the condenser's work is being undone as the liquid travels across in front of the radiator!

I'll get some accurate numbers and pics next time I run it.
I have bought some insulation sleeve today, so I'll try to get before and after numbers too.

It makes sense to insulate the liquid line, will improve performance a little bit. Make sure you use appropriate insulation, don't create a fire hazard for a few% gain.

I vote for insulating the HP line, which would ease the condenser's job somewhat and make for a more efficient system—especially in a Corvette, which can use all the help it can get.

I'll look forward to seeing the system pressures and center-vent temperatures in PSIG and °F, respectively.

That is a good point, Detroit.

You can get sleeving made from woven porcelain or ceramic fiber from McMasterCarr, a huge jobber with 600K different crazy products.
You would have to slit it and affix with those metal zip ties, since it is too late to slip it over the ends. Or perhaps get a larger ID and afix it over the standard foam insulation.

I've been waiting for an 88F+ day to do further testing.
Today is only 77F, but there's a few 91F days forecast later this week.
I also forgot to mention that I've installed a UAC scroll R4 (i know, I've read the negative comments regarding capacity) after replacing a couple of leaky R4's in the last 20 years..... Also have a smaller red orifice - stock is white

So at 77F, windows down, fan on max, engine at IDLE
L 28psi -
H 180psi
Centre vent 45-46F
Lots of condensate dripping off the evap.

I'm still waiting for a hotter day to sneak up on the charge. I've never known exactly how much to charge due the the extra hose length. The liquid line to the evap and the return to the compressor are each about 3-3.5' longer than stock - that must increase the refrigerant required surely.(??) By how much I don't know.
I could calc the internal volume of the liquid line, but unsure how much to consider for the return as it's not going to be liquid full, right??
Stock R12 charge is 2.75lb and I currently have 80%-85% of this amount of r134a in the system.

If I hold it at 1500rpm the compressor cycles a couple of times per minute as the suction pressure drops - due to the slight undercharge and low ambient temp.
I'm waiting to retest on a warmer day, then adjust the charge to keep it running and above 28psi+.

Regarding heat management, I have corrected a few things since my last post.
The flipped and hacked evap box is pretty close to the headers and is therefore very hot to touch. I measured this airspace at 186F. So I made a heat shield and then measured the air temp in the space between the shield and evap box at 116F. I think this along dropped vent temps by 10F to the lowest I ever remember seeing at idle (38F with the windows up).
I also discovered that while on recirc, the hacked up hvac fan box was still drawing in a heap of outside air from the plenum, which I have corrected also.

I did buy some fire rated insulation sleeve for the liquid line where it crosses the engine compartment right in the path of the 190F air blast from the radiator fan. I haven't installed it yet, but did some testing to see how much of a problem this is.
At idle, with the AC running and stabilised, engine up to temp and rad fan running, the HP line into the condenser is 143F, out of the condenser is 114F, then it crosses past the rad fan and enters the orifice at 122F - so it picks up 8F from the engine compartment/rad fan heat. I wonder how that translates to vent temps??
I'm guessing there is an improvement to be had here also? Will it make a significant difference if I insulate this line?

Sorry for the long post. It's working okay now - much better than ever before - and should be acceptable when I balance the charge correctly I think.

Any opinions on the charge weight due to the additional line length, or the value in insulating the liquid line now we know how much heats it's picking up in it's journey across the engine compartment?

Here's a couple of pics of the flipped HVAC box on the LHS of the car - with the heat shield installed.

"the value in insulating the liquid line now we know how much heats it's picking up in it's journey across the engine compartment?"
To repeat, you have a 'vette and thus you need all the help you can get. You are giving us numbers at 77F meaning it is not even summer yet. That 8F is worth getting rid of, especially since the condenser is doing its job nicely (ie approx 30F drop, everyone s/b so lucky). You already asked this question and got at least 2 opinions which were the same.

We do not know where you live. What would be your highest expected ambient in the summer. The more info we have the better we can help you.
Readings at idle do us very little good, we need readings at 1500-1800, doors open, max fan, max cool. (These are numbers when the comp is ON.)
complete with
ambient
Hi
lo
center vent

Calculating the volume of the slightly additional length is a fools errand.
You will have to charge by the seat of your pants. Brad (Bohica) had typed up a way to do this but right now I can't find it. Perhaps in the Archives. It would take me longer to describe it than to do it. I'll keep looking.

Thanks again for your reply.
The above was just a post to communicate some progress and new measurements taken from the liquid line to remove the guesswork from assessing whether it was actually worth insulating, and it seems it is.
I think the old condenser works okay because I have replaced the stock rad fan with a big ass fan from a Volvo that fits perfectly but moves a ton more air.

I acknowledge that numbers at idle are mostly meaningless, which is why I mentioned a couple of times that I will do it again when it gets hotter.
I can't give you those numbers yet as the compressor cycles off if the rpm is held at ~1500 - as it's a bit undercharged currently.
I'm hesitant to add more refrigerant yet as I would rather do it on a hotter day and get it right than overcharge today.

I think Brad's comments you referred to are here:
https://www.autoacforum.com/viewtopic.p ... nown#p6573
but he's talking about a TXV system... I think I'll just strike a balance between the high side multiples of ambient temp 2.3-2.7x would be okay, cycle times and vent temps.
I don't want to overcharge as I'm measuring what goes in to record for the future. If I overdo it and have to take some out, I have no way of knowing what's then left in the system....

"I'm hesitant to add more refrigerant yet as I would rather do it on a hotter day and get it right than overcharge today."
Good plan.
Yes, you found the writeup I was referring to. I do this without even thinking about it. When on an OT system the process is similar. The accumulator stores excess refrigerant.
I think you are more undercharged than you think.
Yes, def wait until a much warmer day since the correct charge is unknown..
Good luck and post back