PDA

View Full Version : General Automotive Questions


captain planet
05-03-2007, 02:15 PM
I have had a debate with a couple friends about two issues when it comes to vehicles and the way they operate. For those of you that know, please interject to set the record straight.

First, and I know the answer to this one, my old college roomate refuses to believe that when you turn on the defroster in your car that the compressor runs (provided you car is equipped with air conditioning). Now I know this only happens above freezing, but he refuses to believe that it runs when the defroster is on. I have even turned it on and off while the truck is running and you can hear the compressor engage and disengage. Anyway, wanted to hear from some other sane people on this. The sad thing about this is, my roomate is in the heating and cooling business.

This one I am less certain about. A friend of mine at work has pointed out that a habit of mine is bad for an automatic transmission. When I am rolling into a parking lot and I am getting close to my parking space, I slide the vehicle into neutral and let the car coast into the spot. He claims that if the vehicle is rolling while the engine is running and you put it into neutral, "it creates pressure inside the transmission." I dont' believe this, but then again I am not a auto mechanic. Anyone of you know about this?

Again, this is for nothing more than an "I told you so" but I must win these arguments.

trickskier
05-03-2007, 02:58 PM
CP, Need to ask you a question regarding the defroster/compressor issue. Are you saying the compressor kicks on even if you have the temperature controls turned up as high as they will go on heat?

As far as the transmission issue, I can't see where putting the car in neutral would cause any additional pressure. As far as I know, all transmissions have a breather on them to relieve internal pressure.

tommcat
05-03-2007, 03:08 PM
Yes the a/c compressor turns on when in defrost mode. since an a/c system is also a dehumidifier that is what gets rid of the moisture on your windshield.
putting the car in neutral doesnt create any pressure or cause any problems mechanically. it is however completely unnecessary and can confuse the computer and effect shift strategy.

chevy08bud
05-03-2007, 03:09 PM
The a/c compressor will kick on when you are using defrost unless the ambient air temp sensor senses that the air temp outside the vehicle is too low. As for the transmission, to the best of my knowledge, this will not cause a buildup of pressure. This is the same thing as having your vehicle in park or neutral. You could do this all day and not have a pressure problem with your transmission. Seems like a little more work and no ability to make speed corrections when parking, but to each their own.

captain planet
05-03-2007, 03:11 PM
CP, Need to ask you a question regarding the defroster/compressor issue. Are you saying the compressor kicks on even if you have the temperature controls turned up as high as they will go on heat?

As far as the tranmission issue, I can't see where putting the car in neutral would cause any additional pressure. As far as I know, all transmissions have a breather on them to relieve internal pressure.
Yea, even if the heat is up and your defrosters are on, the compressor is running. It dries out the air, but my roomate refuses to beileve it. I think if it is really cold, it doesn't come on, but if above freezing, it is running.

trickskier
05-03-2007, 03:24 PM
Yea, even if the heat is up and your defrosters are on, the compressor is running. It dries out the air, but my roomate refuses to beileve it. I think if it is really cold, it doesn't come on, but if above freezing, it is running.

I forgot to add the outside temperature should have an effect on the compressor kicking in........But that doesn't happen much down here in the GATORNATION (sorry had to do it).

P-hat_in_Cincy
05-03-2007, 03:53 PM
I thought I read somewhere that a 'free spinning' transmission at higher speeds is not good (coasting down a long hill), but what about vehicles that are towed behind motorhomes (etc...)?

Compressor kicks on. I think that's been pretty much confirmed.

trickskier
05-03-2007, 03:56 PM
I thought I read somewhere that a 'free spinning' transmission at higher speeds is not good (coasting down a long hill), but what about vehicles that are towed behind motorhomes (etc...)?

Compressor kicks on. I think that's been pretty much confirmed.
Usually vehicles that are being towed have a device that disengages the drive shaft so that the transmission does not spin.

dog paw
05-03-2007, 04:40 PM
One more I TOLD YOU SO! Hehe Most vehicles it's not a set ambient low temp that drops the a/c comp, its the low pessure cut off. The colder it is out the lower the pressure will be in the ac system. They will usually drop off below 25psi

You can coast in netural till the cows come home on the trans thing. Just keep it running... On the late mod GM's you can even through it in reverse if you want to. (not adviseing it) The vehicles PCM will call you names under it's breath and hold off reverse till it slows down.

Ric
05-03-2007, 04:43 PM
both of these actions are harmful to the environment. While convenient, they are very unfriendly to the atmosphere.

I have had a debate with a couple friends about two issues when it comes to vehicles and the way they operate. For those of you that know, please interject to set the record straight.

First, and I know the answer to this one, my old college roomate refuses to believe that when you turn on the defroster in your car that the compressor runs (provided you car is equipped with air conditioning). Now I know this only happens above freezing, but he refuses to believe that it runs when the defroster is on. I have even turned it on and off while the truck is running and you can hear the compressor engage and disengage. Anyway, wanted to hear from some other sane people on this. The sad thing about this is, my roomate is in the heating and cooling business.

This one I am less certain about. A friend of mine at work has pointed out that a habit of mine is bad for an automatic transmission. When I am rolling into a parking lot and I am getting close to my parking space, I slide the vehicle into neutral and let the car coast into the spot. He claims that if the vehicle is rolling while the engine is running and you put it into neutral, "it creates pressure inside the transmission." I dont' believe this, but then again I am not a auto mechanic. Anyone of you know about this?

Again, this is for nothing more than an "I told you so" but I must win these arguments.

captain planet
05-03-2007, 04:48 PM
both of these actions are harmful to the environment. While convenient, they are very unfriendly to the atmosphere.
Dude, your sick.........funny, but sick!8p