AC blowing hot under acceleration

[stevensonjr]

I know that a one way vacuum valve installed in the vacuum system solves the problem. But, all the advice I get says the vacuum line to tap is in the rear right side of the engine. My 2005 Vert has the vacuum lines on the front of the engine with no small lines to tap. I read that 05 and 06 Vipers had different vacuum systems than earlier Vipers. If all this is correct, does anyone have information on installing a one way valve on a 2005 Viper? It’s hot down here in Louisiana, anything around 4000 rpm shuts the cool air off! Thanks for any advice. Bill

 

[kmagnuss]

Oh man I didn't know there was a way to 'shut off' that 'feature'. Drive me nuts in the FL heat.

 

[MoparMap]

I don't think any part of the HVAC system is tied to vacuum on these cars. The doors and actuators are all electronic from what I've seen and dealt with. The only thing I can imagine might be vacuum controlled would maybe be a hot water shut off valve, but I don't think the Viper uses one of those either.

Some cars will drop out the compressor at high rpm as a safety/for extra power though. Maybe that's what is going on?

 

[Old School]

The engine controller disengages the compressor for anything above light acceleration for a couple of seconds. This is tunable with HP tuners.

 

[stevensonjr]

Nope, compressor is never automatically turned off and All of your air con and heating vents are controlled and held open by vacuum lines from the intake area, not electricity. My question is not “ how does it work?” But how do you fit a one way valve in the front vacuum lines to maintain vacuum in the system during hard acceleration..I have a 2005 Vert. Earlier Series 2 cars have the vacuum lines in the rear of the engine, the solution for them is similar but on the opposite end of the engine for series 3 cars. Looking for someone who has solved this problem on a 05-06 car. Thanks, Bill

 

[MoparMap]

The vents aren't controlled by vacuum, they are controlled by electric actuators on top of the box. I have the service manual in front of me and have disassembled my entire system because I had a broken blend door. There is no vacuum control on the system.

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Note how it says the blend door and recirc doors are operated by electric actuators.

You can't find a vacuum line to tie into because there isn't one in the HVAC system to tie it to.

 

[Viper Specialty]

Nope, compressor is never automatically turned off and All of your air con and heating vents are controlled and held open by vacuum lines from the intake area, not electricity. My question is not “ how does it work?” But how do you fit a one way valve in the front vacuum lines to maintain vacuum in the system during hard acceleration..I have a 2005 Vert. Earlier Series 2 cars have the vacuum lines in the rear of the engine, the solution for them is similar but on the opposite end of the engine for series 3 cars. Looking for someone who has solved this problem on a 05-06 car. Thanks, Bill

Bill,

You are incorrect, trust me. What you are stating applies to Gen-1/2 cars, NOT Gen-3+. 2003+ has no vacuum actuators of any kind in the HVAC.

Gen-2/3 *BOTH* have an A/C compressor disable tied to TPS, but Gen-2 also loses actuator vacuum, causing the vents to close under high load which is far faster to notice than compressor shutoff, which takes a few seconds for air temp to start rising.

If you want, I can edit this in a flash for you so that it is much harder to cut off, but unless you are lugging in high gears this is rarely an actual thing.

 

[BoondocSaint]

I have plenty of popcorn for this lol. Learning plenty about how these systems work. The extent of my understanding was replace o-rings, then replace the one nobody talks about, then top of the AC again. 2nd gen (GTS) for reference.

 

[stevensonjr]

Ok, now I know that gen 3 cars are different, what is shutting off the ac every time I get on it. Hot air starts blowing out of the ac vents under hard acceleration. Cool air starts again when I back off or idle in traffic. Does this every time. The ac system works well in normal driving on the hottest of days. Shut off happens every time I run thru the gears. Looking for solution. Thanks, Bill

 

[stevensonjr]

I am very old school. I don’t know what “edit in a flash” means. I’m still enjoying the car at 82 but obviously don’t have a grip on anything past carburetors and such. My wife says just slow down and it won’t happen, I’m not quite ready to accept that yet. Thanks, Bill

 

[stevensonjr]

Dan, if I’m reading correctly, choosing the recirculating mode should reduce the amount of temp change during acceleration. No more blast of hot air, no outside air introduced. Is this correct? Thanks, Bill

 

[Viper Specialty]

I am very old school. I don’t know what “edit in a flash” means. I’m still enjoying the car at 82 but obviously don’t have a grip on anything past carburetors and such. My wife says just slow down and it won’t happen, I’m not quite ready to accept that yet. Thanks, Bill

It means change the programming so that it is harder to have the A/C compressor disengage during throttle changes.

It sounds like either you are lugging the engine, very aggressive on the throttle, or for some reason your car is cutting off the compressor earlier than they typically would.

Lugging the engine results in higher throttle positions for acceleration, and as a result, easier A/C shutdown.

 

[Viper Specialty]

Dan, if I’m reading correctly, choosing the recirculating mode should reduce the amount of temp change during acceleration. No more blast of hot air, no outside air introduced. Is this correct? Thanks, Bill

Recirc Mode may help slightly, but not all that much.

 

[stevensonjr]

Dan I’m down shifting to the lowest gear before accelerating, I may be powering up too quickly as I’m used to driving my Cobra like that, of course it’s not air conditioned.
What would changing the programming entail? I fitted 3:55 differential gears and got rid of the crossover exhaust under the cockpit. Other than that it’s stock. It’s very hot and humid here in South Louisiana and it’s irritating as hell every time the vents blow hot air! Thanks, Bill

 

[Viper Specialty]

Dan I’m down shifting to the lowest gear before accelerating, I may be powering up too quickly as I’m used to driving my Cobra like that, of course it’s not air conditioned.
What would changing the programming entail? I fitted 3:55 differential gears and got rid of the crossover exhaust under the cockpit. Other than that it’s stock. It’s very hot and humid here in South Louisiana and it’s irritating as hell every time the vents blow hot air! Thanks, Bill

In general, this is not a common complaint for G3+, as you have to be pretty far on the pedal for A/C cut to occur.

The first thing you should do is make absolutely sure you dont have some other weird issue. A TPS sensor out of range can cause this. I assume you have no codes? Do you have a scan tool able to read TPS and see if it has a smooth voltage output across the range?

Beyond that, if you are stabbing the throttle like a madman, this will happen. There is a hysteresis to A/C function so that its not flipping on/off constantly, so that stab at the gas cuts it, and then it wont come back on until you really let off... where if there was no stab, it may never have actually cut in the first place. If you are stabbing at the throttle, thats a driving issue, not a programming issue.

I caution the use of programming changes to alter the way things are "supposed" to be. If you are sure there is no other cause, then the programming can be altered by mailing me the controller, or, I can send you an SCT Flash Device and you can load the file in the car yourself.

 

[MoparMap]

I remember people saying the gen 3 hood vents were also not great for this and one reason the gen 4 vents were redesigned. At least if you have the controls on outside air, the hood vents tend to feed right into the A/C inlet at the base of the windshield on the passenger side. I think especially when you take off from a stop you might get a big gulp of hot air into the inlet when you first take off, but that should be pretty limited I would think. Recirc mode should in theory also eliminate that as a cause, though then you may be pulling hot air from the cabin depending on your exhaust setup.

 

[stevensonjr]

Thanks for the information Dan, I do have a scan tool and the booklet that ID’s the codes. I’ll look around with that and see if any codes are showing. Could be just the old man behind the wheel. Thanks, Bill

I remember people saying the gen 3 hood vents were also not great for this and one reason the gen 4 vents were redesigned. At least if you have the controls on outside air, the hood vents tend to feed right into the A/C inlet at the base of the windshield on the passenger side. I think especially when you take off from a stop you might get a big gulp of hot air into the inlet when you first take off, but that should be pretty limited I would think. Recirc mode should in theory also eliminate that as a cause, though then you may be pulling hot air from the cabin depending on your exhaust setup.

 

[stevensonjr]

I’ll check out the recirc mode for problems there. Thanks all, Bill

 

[kmagnuss]

Mine does the same thing, even when on recirc.

 

[Viper Specialty]

Mine does the same thing, even when on recirc.

Can always deal with this... and your TPMS at the same time!

 

[stevensonjr]

TPMS ??

 

[Viper Specialty]

TPMS ??

Unrelated. He has a Tire Pressure Sensor Issue he posted about elsewhere.