OK guys, Its 90 degrees out in Texas (or CA or AZ for that matter) and 30% humidity. Your car has been sitting out in the sun for 3 hours or so. How long does it take your a/c system to remove the heat in your car to make it comfortable?

Are we trying to overcome general physics and expect the car to be comfortable within 5 minutes?

(I'm especially interested to hear from Morrison with his parallel flow setup).

Do tinted windows work well at reducing the load when the car is first started up? How would you rate the tint's ability to reduce the heat load on a scale of 1 to 10?

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

After 3 hours, the tint won't make too much of a difference. I find that tint is most beneficial when you're sitting in the car - it prevents the direct light (and heat) from hitting your skin. It does help for short stops, such as running into a fast-food place or a quick stop at a store.

90 degrees is really no problem. I can have a tolerable interior in five minutes IF I roll down the windows for the first 100 yards or so of motion to purge the bulk of the hot air and I get the car in motion and not stop for five minutes for a congested traffic situation.

Now 108 degrees? That's a different story. But even in that situation if the above situation exists and I can get and keep the car in motion 10 minutes will have me acceptably comfortable.

Have a great day,

Larry,

Do most of the older mb's (123 and 126) have pretty poor ac performance in stop and go traffic, (ie the system doesn't really blow that cold while at a traffic light).

I have found that the engine really needs to see 1500 rpms or more for the compressor to start working well.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

Eric, what you are seeing is the effect of the primary limiting factor in any ac system... that is " airflow across the condensor"...
You might get away with just putting in one of those high performace aux fan.... Italian I think... Spo ? Carlisle auto air in San Antonio has them listed with the airflow rate.... some really put a lot of air across the fins.... I will be doing this myself... and may put the P condensor in addition.... but am thinking about doing just the fan as a test....in order to tell later exactly how much better the P condensor is...

I concur with Larry. Ninety degrees isn't too big a problem if you are driving. Anything over 40MPH for five minutes ought to do it.

All the old diesels I've owned or driven had marginal a/c in stop-and-go conditions. It takes a long time for a heat soaked 123 to get comfortable if you start it up and just let it idle. I think there are a couple of issues at play. For one, the compressor just doesn't do enough "compressing" at low engine speeds, and the very low idle speed of the diesels exacerbates this problem. You can see this on your guages - the low side is about 40PSI at idle, right? Drops to 25 when you rev the engine to 1500 RPMs. Evaporator temperature corresponds directly to low side pressure, so the evap is warmer at idle than when driving. The older cars don't have great condensers or condenser fan systems either, so they can't reject all that much heat at idle.

Are you aware the 123 cars use 20% fresh air even when in recirculate mode? One of the standard Texas hacks is to modify the system to use 100% recirculated air. On really hot, humid days this will get you about 5 degrees cooler discharge air.

A good window tint helps a lot! Good tint reflects a high percentage of the infrared spectrum, which reduces heat gain. It helps the car cool down faster when you do switch on the air, and you don't feel as much heat sitting in your hot car. I have a metalic tint on my wagon and it really makes a difference. It's not mafia-don dark, but does reject mucho heat (and ultraviolet too).

- JimY

Are the NipponDenso compressor any more effecient?

One of my mechanics is finishing up a 617T into a 70's era 230sl. Its an extremely tight fit. Utilizes a ND compressor (custom fitment) which I understand is a better compressor than the R4, just not sure why. Its certainly more costly.

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

It depends on how hot it is outside, but I usually open the windows for a couple minutes and then turn the AC on. The outside air, depending on the temperature differential, will cool the car to a certain point much more quickly than the AC. Typically the AC should be blowing nice cold air in about 30 seconds, and if it's blowing on you, you should feel it pretty quickly. I'd guess a good AC system will probably take something like 10-20 minutes to cool the average interior temperature from, say, 120 to 80 degrees. The thing is that there is a lot of material to cool, and while a good AC system will make you feel cool pretty quickly, it takes a lot more to truly cool the interior.
Tinting helps a lot, especially considering that a lot of the heat you really feel is from the sun shining on you. I'd guess that tinting probably reduces the amount of heat energy coming into the car by something like 30% depending on the amount of sun, glass area, interior color, etc.
As for performance at idle, usually the two main issues there are airflow and compressor size. With the system on my Fairlane, a parallel flow condenser, electric condenser fan, and a Sanden SD510 (10ci), it pulls down pretty well even at idle. I'm not sure what the typical size of the 123 and 126 compressors is, but if it's 8ci or more I'd think it would be plenty. Then again, I'm not sure how the flow of the York and R4 compares with a swashplate design like the Sandens, but I would guess it's not as good.

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Once and future king:
'64 Ford Fairlane w/approx 238,000 - looks rough, but amazingly reliable if you know how to look after it; I will soon begin work to totally restore and modernize it.
Family vehicles that I lay some claim to:
'78 300D w/approx 350,000 original, '62 Ford F100 4x4, '90 Ford E150 w/171,000 original

Turn the ac on and roll down the windows.... a car out in the sun can easily get to 150 degrees... so use the ambient air to get back to the outside temp... and it takes a minute for the ac to get its pressures up to snuff...
From everything I have read ( in addition to last posts) window tinting can make a lot of difference.... and particularly on the moving green houses.... I mean the wagons....

Does anyone have a car cover they use out in the heat ?

One could just fit over the cabin area on a sedan and make a lot of difference... and be light enough to throw up there without much tying down....

I am thinking of making a cover like that...

I don't recall many days that are 90 degrees and 30% humidity..... it's usually a lot more humid here at that temp. then the humidty drops off as it gets hotter. Anyway, cracking the sunroof if you're forced to park in the sun for several hours seems to keep things a little cooler and leaving it open a little to shove all the hot air out as the AC starts to cool helps along with the windows being open a little. Also make sure your aux. electric fan is working properly, that seems to help a lot in stop and go traffic. Mine cools off pretty fast if you get moving but it seems to take a while for it to get comfortable (dry the air out).

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

Eric,

Actually I have had good performance from my 123 and 124 cars with R12 in stop light driving. Everything has to be perfect though. There is not much extra capacity, that's why they don't convert well to 134 without more condensor.

Compressor efficiency has nothing to do with a/c effectiveness. If you have a more efficient compressor it will just cost less drag on the engine.

The controlling element in a/c efficiency is the condensor, providing of course that the compressor has adequate capacity which they all do.

Leathermang,

A cover like you describe should be easy to find from a German aftermarket supplier. They are quite popular in Germany for the Winter to keep the snow off the glass.

Have a great day,

Leathermang is on the right track (look at all the non-commercial
aviation areas of your local airport) [or Marinas].

P-flow condensers , secondary evaporator,electrically powered
compressors (with a scary retrofit alternator BALMOR) .............
sustaining lifeforms in this blastfurnace we call the South.

One of those windshield sun shields will help too. They're about $7 at Target, maybe cheaper at Wal-Mart. I had the car sit out all day long in the heat, and when I got in, the car was considerably cooler. That will help reduce heat load.
-Joe

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

I should have been a bit more specific when I asked about effeciency of the R4 vs. a ND compressor. I turn on the ac its like goodbye turbo. The compressor eats up power. Same results on both 300D's.

Does a ND compressor require any less HP to rotate than an R4?

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84 300DT Puke Yellow. Totalled after 438,000
84 300DT Orient Red. 169,000 (actual mileage may vary)
2002 Explorer EB (wife's)

I do not know the relative power requirements for the ND compared to the Delco....
However, since both are rotaries I suspect that difference is almost zero...
I think the differences when choosing between the two may come from things like the ND being easier to fit along side an engine compared to the (BIG) pancake design of the Delco....and maybe the ND has a crankcase to store oil...... and potentially in reliability... particularly in the rebuilding of them.....
I think the fault line in compressors is between the york type... which is basically an inline two cylinder engine... with the accompanying problems with mass changing directions... vibration...the rotaries chop that up into lots of small compressions in little movements...