Yes, it does shut off at WOT reguardless of the RPMs.
I noticed this on my last road trip: it seems to be connected to the throttle position sensor rather than engine rpm. If you goose it in 6th, even though RPM goes up only a little, the vents blow warmer air for a few seconds...
About two years ago on the morgue site, a user named luc made a compelling argument that the AC does NOT shut off, it's actually a loss of vacuum pressure. A lot of people disagreed with him, but he insisted that by installing a vac resevoir, he would not lose cool air under any circumstances. I think he even had photos of his setup. At any rate, I seem to recall he had some very detailed instructions. Apparently a resevoir like this is common on other vehicles.
This sounds reasonable to me. In every other vehicle I've ever driven, including those which kill the AC compressor under acceleration, if you turn off the AC the system still blows cold air for at least a few seconds or more. But in the Viper, the switch to hot air is instant and extreme. This suggests to me there is more going on than simple compressor shut-off, which shouldn't interrupt the cold air flow unless it happens for an extended duration. (My Ram will blow cold air for a good five minutes after the AC is shut off.)
About two years ago on the morgue site, a user named luc made a compelling argument that the AC does NOT shut off, it's actually a loss of vacuum pressure. A lot of people disagreed with him, but he insisted that by installing a vac resevoir, he would not lose cool air under any circumstances. I think he even had photos of his setup. At any rate, I seem to recall he had some very detailed instructions. Apparently a resevoir like this is common on other vehicles.
This sounds reasonable to me. In every other vehicle I've ever driven, including those which kill the AC compressor under acceleration, if you turn off the AC the system still blows cold air for at least a few seconds or more. But in the Viper, the switch to hot air is instant and extreme. This suggests to me there is more going on than simple compressor shut-off, which shouldn't interrupt the cold air flow unless it happens for an extended duration. (My Ram will blow cold air for a good five minutes after the AC is shut off.)
I remember that discussion, and since saw a technical service bulletin(?) that says the cars should not be doing that - I haven't bothered to follow up though.
Take this part and install it at the rear of the passenger side intake tube where the small hose is. Put it between the small hose and the manifold. You will have to find a piece of hose to go from the end of the valve to the manifold. You can use any length of hose you want so you can tuck the vavle away so it is not visible. This is a one way check valve. List price is $6.20 and the part number is 4677204. I have done a ton of these and it work everytime. Hey, for 6 bucks, its gotta be worth it!
DW
Last edited by DW@A.R.T. : July 17th, 2006 at 06:42 PM.
David,
can you take a picture of what youre talking about here so we know which hose youre talking about?
All right, I'll do that, gimme a few....but I will be damned if I will order you one! Ya know what I mean, I have some parts here with your name on them, NO SHOW!!!!!! j/k
Pics coming up shortly.
Here it is shown on a Gen1 (sorry no Gen2 in the shop with factory manifold), Gen 2 is basically the same location. The small black vaccum line, I sat an orange magnet on the intake to point at the hose. This hose is the sole supply of vaccum to the AC system. Hope this helps,
DW
Last edited by DW@A.R.T. : July 17th, 2006 at 06:41 PM.
sounds like it does AND there is a loss of pressure which is why it goes hot so quickly. ???
Basic explanation: When you go full throttle your vacuum goes to zero and that lets air door/s close/open in the hvac system. If you install the check valve it will keep the doors where they need to be. Sounds like the compressor could still be engaged (or not)
Why wouldnt the factory have caught this issue during testing and after making nearly 12,000 cars with AC? Im guessing there is a reason they want the AC to shut off at WOT? The idea that they did it to save HP doesnt make a whole lot of sense unless there is a clutch on the AC taht also shuts down the compressor for additional power? But the amount of HP it might save at WOT should be negligible...think its more of a wear and tear concern for the AC compressor assuming that there is such a "clutch"?
I think it may be wear and tear "if" the clutch disengages at full throttle. Less powerful cars and it may be a power issue. The Viper a/c is like most all a/c compressors and has an electric clutch on the front of the compressor. It may or may not cut off at full throttle, but the loss of vacuum is causing the air doors in the hvac to change resulting in the immediate loss of cool air.
Why wouldnt the factory have caught this issue during testing and after making nearly 12,000 cars with AC?
The car does come from the factory with a vacuum check valve. It is flat and about the size of a quarter. It is locate behind your radio in the ac system vacuum harness. You ever pulled your radio? Much, much easier to install this one outside. The valves fail and the one I posted is now standard issue on all cars that still use vacuum for the ac system, which is none. All cars now use electronic actuators for the ac, yes, even the SRT. The factory probably doesn't give a rats ass.
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