A/C Efficiency

[cheekychimp]

Okay after looking into this a little more closely and speaking to a few members via PMs, it doesn't really look like a DIY A/C system is going to be any more efficient than the factory one. Obviously I am putting a lot of strain on my A/C because my cars live in unshaded car park spaces all of the time they are at home, I live in an area of high humidity and temperatures in the summer regularly surpass 33 degrees celsius or 90 degrees fahrenheit.

Any ideas on improving the A/C efficiency. I've been looking at a few possibilities.

(1) Increasing the efficiency of the stock system

SUCTION LINE HEAT EXCHANGER I have seen this company advertise before but can a SLHE really improve the system efficiency?

I also see that some residential A/C manufacturers employ water rather than air cooling. Would a water-to-air heat exchanger take more heat out of the system and improve the A/C efficiency?

OR could I install one of those water sprayers like they use on intercoolers for race cars? It would probably use too much water to allow me to run it all the time but I am thinking that on start up it might help get initial cabin temperatures down ... thoughts?

OR

(2) Add a secondary system. 12V electric A/C compressors do exist! I know hybrid vehicles like the Prius also use electric A/C compressors but I am not sure that these use a 12V DC power supply and may be run off the vehicle drive batteries.

Whilst somewhat complicated, I am thinking a small additional electrically driven secondary system could have benefits. When the vehicle is running a secondary system remote (possibly trunk) mounted could feed air into the vehicle via the rear parcel shelf. Venting/airflow for the condenser/heat exchanger could be an issue (unless an water-to-air solution was installed). It is also feasible (subject to power draw) that the A/C system in the rear could be run for short periods whilst the vehicle was stationary with the engine switched off to comply with idle/emission laws.

I know this is an issue that doesn't concern most of you guys but over here cabin temperature is critical to enjoying driving the car. Any thoughts? Some people swear by water-to-air intercoolers. Is it worth looking into replacing the condenser with a water cooled one?

Paul.

 

[Barnes]

In my opinion, keep it simple. The easiest way, in your case, to make your A/C system work better is to A)Install a larger/more efficient condenser and B)Install bigger fans.

The more heat you reject out of the condenser, the more heat you remove from the cabin; i.e. the colder the evaporator is.

The next step would be to scale up the entire A/C system. I think an auxiliary system would be entirely more complicated than just scaling up the existing system.

 

[IncorpoRatedX]

+1 for better fans and possibly new components.

 

[SouthCaliVR4]

if you can keep the system r12 that will help. cleaning the condenser & straightening the fins will help. Put some kind of shut off valve on the heater core, the core in these is bypassed by the cabin air flow but coolant still circulates through the core & would be another source of int heat.

Be sure to replace the receiver dryer & expansion valve. clean the air ducts & the squirrel cage (int fan) to to assure good airflow, an issue mine had. with all of that & if it's legal to tint the windows the a/c should work well as designed. tinting the windows makes a huge difference, while you can't do much for the windshield the rear window shape really lets solar heat up the car & can make even a good working system fight to maintain int temps.

The drain, remove & clean out all debris in the hvac box, any moisture trapped in the box will freeze on the evap core & reduce the airflow over the fins again reducing efficiency.

Mine with a clean box, condenser & r12, along with (lightly, 19%) tinted windows keeps the car plenty chilly even north of 100deg. of course my car is white which also helps. Plenty of airflow over the condenser is also a biggie, I.e. a pair of big fans up front.

 

[Barnes]

Quoting SouthCaliVR4:
Put some kind of shut off valve on the heater core



I understand the rationale behind this, but I would be cautious about doing this mod. The coolant system in our cars always has a flow path because the heater core always has coolant circulating through it. The throttle body coolant lines, turbo coolant lines, and oil cooler lines also serve this function. We don't know what considerations that went into designing the cooling system in these cars. It might cause problems if you have no bypasses in the system, i.e. no TB coolant lines, no turbo coolant lines, no oil cooler coolant lines, and a heater core line blocked off.

I would suggest if you do put in a heater core shutoff valve, make it a bypass valve that will create a loop between the heater core feed and return line. That way you still have that bypass intact.

 

[iceman69510]

The EA3 and EA8 Galants in the US added the heater core bypass at some point to improve A/C performance. I can get you a part number for it, but not sure if you can get it all the way over there in Japan. Errr, I mean Hong Kong. /ubbthreads/images/graemlins/grin.gif It may have been a US market only part.

 

[Wizardawd]

Lots of US cars come with bypass valves. Goto any parts store and find the one that would best fit your app. Basically just get the hose size correct. They were usually controlled by either a vac. motor or directly via a cable. But....some of these valves were a dead-end style shutoff rather than a bypass. Which means there was a bypass somewhere else in the system.

Like this:

For our cars, you'd want to use one like this:

Cable operated and a true 'bypass', routes coolant in a loop.

Another option is passive improvements. Color of the car, window tints and films, etc. Something that would make the job of the current A/C system easier. Just remember, don't expect 30deg out of your vents when the inside of the car is 120deg. A/C just doesn't work that good. At least not R134 systems. R12 on the other hand.....

Wiz

 

[cheekychimp]

Quoting iceman69510:
The EA3 and EA8 Galants in the US added the heater core bypass at some point to improve A/C performance. I can get you a part number for it, but not sure if you can get it all the way over there in Japan. Errr, I mean Hong Kong. /ubbthreads/images/graemlins/grin.gif It may have been a US market only part.



I would really appreciate it if you could get that part no. for me, or even price the part up and maybe send me a couple. This sounds like a must do! My car here in Hong Kong still runs on R12 so I am a bit disappointed with the current performance. Perhaps as has been stated it might be worth investing in some new parts for the stock system as it is used everyday and is every bit as important as everything else in the engine bay. I remember Curtis had some sick VW fan setup on his scirocco radiator with a huge motor and belt drive to run the second fan. That might be another option. Since the scirocco is the same size as the condenser a shrou could be built and the fans configured either as push or pull.

Not to flog a dead horse here but water is supposed to absorb four times as much heat as air. Complications aside, does anyone thing a water-to-air condenser would increase the A/C efficiency?

 

[Dan D]

What condition is the current A/C system in? New/Old parts - Exansion valve, drier, o-rings, compressor? I learned a lot about what makes an A/C system work well and what doesn't over the last couple weeks as I've been re-establishing mine (after 10 years of brokenness).

With R134a, I'm getting 48-52F vent temperatures. I don't think Houston is quite as bad as Hong Kong, but it is a similar climate and right now our temps are high 90s, low 100s with 80-95% humidity. It turns out that a rebuilt compressor helped, a new expansion valve helped, a new drier helped some more, most improtant though was vacumming the crap out of the system (1 hour at 29.7 inhg) and then charging carefully, being certain to purge lines to keep air and moisture out while changing cans. I dialed in the pressures and low and behold my vent temps got nice and cold.

It took me two full rounds of parts and charging to get it right, but the at the end of the day, new parts and proper procedure and charging made the difference.

 

[cheekychimp]

Dan,

Thanks for sharing that. It seems that I might have to bite the bullet and order up some parts and go to see an A/C specialist to get the system vacuumed/purged properly. Is there any way to check if the compressor is up to scratch? I haven't measured vent temperatures but I am running R12 and I am damn sure my vent temperatures are not that good. On my previous VR4, with the electronic digital control set to 17 degrees, after 15 minutes I would have to turn the temperature up because it used to get too cold. This car just kees pumping out air and it gets comfortable but not cold.

You make a valid point however. The system should be working optimally before thinking about further upgrading it. Time for a full A/C service I think.

 

[SouthCaliVR4]

If there is a problem with the compressor it will show on the gauge's when they charge the system. there has to be a good differential high side to low side. Average for a good system is around 30 low & 200 high (that's in psi) or 200 kpa/low & 1400 kpa/high. If the high side is not getting up there you will never get enough differential to have a good functioning system.

whoop, edited. had kpa as bar, that scale is hard to read on my machine & I never use that scale. /ubbthreads/images/graemlins/blush.gif

 

[cheekychimp]

Thank you, that will help a lot! /ubbthreads/images/graemlins/worthy.gif