a/c and acceleration
 

I have had my diesel since January and have been very happy with it but just in the last week when using the air conditioning I have noticed a very pronounced decrease in acceleration when the a/c is running. I wonder if this is normal with these cars or do I have a problem.
Jeff

1981 300TD-T 197K miles

a/c & accleration
 

aajef,

Perfectly normal to loose power when the a/c is on. If you've a problem reach over and switch it off when you want more power. Otherwise rig a off switch whcih next to your kickdown switch under the accelerator pedal. The when you push the pedal to the metal, it'll cut the a/c off, when you let up it's back on.
Ben

When I first got my 300CD, I was worried that my AC would really bog down the car.
Nope! I notice very little difference in power!

Could be your pump is either overfilled, or on the way out...

I know this is a subjective discussion on what is "losing power", but suffice it to say, that my diesel engine loses less power than a gas engine when the pump is switched on.

normal
R

Normal
 

I tend to click it off when I'm "taking off".

Remember, HP is less than 100HP. I will have an impact. It is part of the charm of owning a diesel.

JCD

There was an aftermarket device that turned off the ac compressor when one accelerated... it worked off vacuum... and it was one of the few gizmos which the independant testing agencies said actually worked to save gasoline.. I do not know if the unit could be made to work with diesels... but the company that made it might know...this device is at least 20 years old....I am sure I saw it and other items which claimed to save gas in something like Popular Mechanics magizine, etc... Greg

Ok,, try this site...

http://www.ftc.gov/bcp/conline/pubs/autos/gasave.htm#**

it is in the category of "accessory modifiers" ...they are evaluating it just in terms of saving fuel without increasing emmissions... but the point is there may be some devices which will automatically cut out the ac compressor depending on how hard you put the accelerator down...

Well I'm with Ed on this one. Some cars I have owned react very noticeably when A/C is on, whether idling or under acceleration. But my '85 300CD seems much less bothered. I hardly notice when the A/C is on. I have assumed that it is due to the diesels torque.

Can't imagine why one 300D would be much different than another, unless there is something about the A/C pump that can cause additional power to be lost.

Maybe its just different drivers.

Nic

240 A/C repair
 

As the weather heats up I ponder:
Just got a 240 D which I discovered has a cracked pully on the compressor. Mechanic Friend says just as well, don't need any less power. Just roll down windows. (Wish I'd known that before replacing AUX Electric fan.) Should I get a new GM compressor and dryer and convert to R34? or go for the rubber bladed electric fan suction cupped to the dash?

Thanks

J

My 240D has a noticable acceleration loss with the compressor engaged. If I really need a little extra, I turn it off. I live in Alabama, and my enjoyment factor of driving my car would be much less w/o A/C. If I lived in New York, I might be inclined to live w/o, however, my perfectionist tendencies want all systems to work, even if I don't use them that much. I've got my cc actuator apart on the workbench - even though I don't really need cc that much.

I am surprised that there is as big a difference in performance with the turbo models.

It also has been converted to R134A, which is not as cool as with the R12, but it takes the edge off the extreme heat. In northern climates I doubt this would be very noticable.

FWIW,

My 300SD acceleration is substantially reduced with the AC on. If I really need to get moving in a hurry I flip the switch off and manuall downshift to 1st.

My 85 300 is a bit slower with the compressor on, but maybe only in my head... I notive my car is slower on hot days, than it is on say cool (but not cold) nights. Strange, I take notice to the relative humidity, for this will effect your fuel pump, transmission and anything else that works off vacuume (read everything in the 300D...)

Most A/C compressors consume 4-8 HP depending on condition, which is not enough to cause a *major* change in acceleration.

However, A/C compressors add a great deal of inertia to an engine, so they require a lot of instantaneous torque. What this means is that your car will "feel" a lot more sluggish off the line. Diesels are not known for their throttle response, and A/C will further reduce this response. But, the acceleration once you're underway will be almost identical.

I've tested this theory and I make it to the same speed (give or take a few tenths of a MPH) at a certain benchmark with the A/C on OR off. The car feels a lot slower because it no longer has much of a jump off the line, but that obviously has very little effect on acceleration overall.

-Joe G.

I've noticed it too! It seems OK but that first instant when I push the pedal down I wonder if I'm going to move at all.

Is ther a way to tell if the A/C has been converted? I don't know what refrigerant is in there so other than contacting the previous owner, is there a way to tell?

While AC is discussed with diesel engines... I have a question about the merc AC systems. I have a 1984 190D 2.2, and the AC really doesn't give me the cooling that I like when it's around 80 F out. I have a few cans of the freon... I can add some, but once I open the can it's use it all or throw away what you don't use. So I want to know if adding some will help to make it worth throwing away a can. Should I get it upgraded to the new refridgerant? Would it make it blow colder? I am comparing this to all other car's I've driven, mostly chrystler and ford products. My brother added refridgerant to his 90 ranger, and he said he was suprised there weren't ice cubes comming out his vents. And I agree with him it's too cold... which wouldn't be a bad thing with this car, since leather seats make you all sweaty.

Well any ideas or anything will be greatly appreciated. Thanks!

R-134a uses quick connect style fittings versus the older threaded/schrader valve fittings used by R-12. This is how you can identify the system. Most retrofit kits include R-134a style fittings that screw onto the R-12 fittings. The fittings are required to match the refrigerant used.

The best way to maximize A/C system performance if you are having problems is to have the system connected to a good A/C recycling machine. Totally evacuate the system, then pull a vacuum on it for about 15 minutes. Recharge the system to factory spec capacity, then add a bottle of BG Frigi-Quiet oil supplement.

The vacuum is important because it removes any air or moisture in the system. These 2 contaminants adversely affect A/C performance.

The charge must be correct in order to acheive maximum cooling. Too little or too much will result in less temperature change.

-Joe