AC goes warm on acceleration

Posted By: Telvis

AC goes warm on acceleration - 04/19/14 05:14 AM

I have a 73 challenger and recently rebuilt my heater box with a Detroit Gasket kit and installed a compact compressor and updated AC kit from Bouchillon Performance. Everything works fine except my AC goes warm when I accelerate. Noting changes as far as where the air blows. It comes out of the dash as it should. The heater diverter valve is working properly. The weird thing is the driver vent air stays cold. The warm air comes from the ash vents on the passenger side. When I lower the RPMs the temperature gradually cools down and goes back to cold. I am assuming it has something to do with the vacuum to the heater box. If I change the settings everything changes as it should. I know the lines are all connected correctly. I installed a one way check valve where the main line connects to the engine. I thought that might help retain vacuum if the motor lost vacuum during acceleration. It didn't help. Any ideas?

Posted By: RapidRobert

Re: AC goes warm on acceleration - 04/19/14 11:18 AM

You'd sure think if the one way check valve was properly retaining the vacuum that you'd be good since the only thing that is changing IS the lack of vac when you accellerate. I'd give Bouchillon a call. EDIT I wonder if you have a leak in the vac line/vac operated valve/switch (whatever it is) downstream from the check valve & without the constant vac from the eng when it gets capped off (with the check valve) that it simply bleeds out? I'd pump it up with a hand held vac pump (they're reasonable & a necessity for dist modding)

Posted By: 63stabamatic

Re: AC goes warm on acceleration - 04/19/14 12:29 PM

Just a thought. Is it possible your A/C compressor is turning off when you accelerate? The reason I'm asking is I remember years ago some Mopars, mainly slant 6, and others turn off the compressors during hard acceleration for more power, especially passing and hills.

Posted By: B5 Bee

Re: AC goes warm on acceleration - 04/19/14 12:36 PM

Quote:

Just a thought. Is it possible your A/C compressor is turning off when you accelerate? The reason I'm asking is I remember years ago some Mopars, mainly slant 6, and others turn off the compressors during hard acceleration for more power, especially passing and hills.

Don't know about the slant sixes deactivating the AC but the 440 cop cars did when in pursuit mode.

Posted By: 70Cuda383

Re: AC goes warm on acceleration - 04/19/14 01:58 PM

I would be inclined to think that you have a vacuum leak that is causing the blend doors to move when you go WOT and lose manifold vacuum.

If your AC is hooked up on switched power and relays with line pressure switches (i.e. totally isolated from the engine) then it has no way of knowing when you go WOT and shutting off the compressor.

Posted By: cjskotni

Re: AC goes warm on acceleration - 04/19/14 03:07 PM

Quote:

I would be inclined to think that you have a vacuum leak that is causing the blend doors to move when you go WOT and lose manifold vacuum.

If your AC is hooked up on switched power and relays with line pressure switches (i.e. totally isolated from the engine) then it has no way of knowing when you go WOT and shutting off the compressor.

The HVAC system on these cars has no connection what so ever to the engine besides the vacuum on the blend doors. The only way the compressor can shut off (in A/C mode) is with a low pressure situation from the drier sensor which will break the clutch circuit if the pressure drops to save the compressor from damage.

Replace the check valve on the vacuum harness. They have them in the HELP section at Advance Auto and similar chain stores. The next thing would be the vacuum servos themselves which could have a slightly torn diaphragm causing it to leak down prematurely and close the bend doors the moment vacuum drops.

You can also test this theory if you pump the brakes (if power) repeatedly and listen/feel for the doors to close while the A/C is on. This will have a similar effect to WOT on the vacuum.

Good luck but don't overthink this!

Posted By: Telvis

Re: AC goes warm on acceleration - 04/19/14 06:27 PM

Quote:

Quote:

I would be inclined to think that you have a vacuum leak that is causing the blend doors to move when you go WOT and lose manifold vacuum.

If your AC is hooked up on switched power and relays with line pressure switches (i.e. totally isolated from the engine) then it has no way of knowing when you go WOT and shutting off the compressor.

The HVAC system on these cars has no connection what so ever to the engine besides the vacuum on the blend doors. The only way the compressor can shut off (in A/C mode) is with a low pressure situation from the drier sensor which will break the clutch circuit if the pressure drops to save the compressor from damage.

Replace the check valve on the vacuum harness. They have them in the HELP section at Advance Auto and similar chain stores. The next thing would be the vacuum servos themselves which could have a slightly torn diaphragm causing it to leak down prematurely and close the bend doors the moment vacuum drops.

You can also test this theory if you pump the brakes (if power) repeatedly and listen/feel for the doors to close while the A/C is on. This will have a similar effect to WOT on the vacuum.

Good luck but don't overthink this!

I know all of the vacuum "pots" or whatever they are called are good at the heater box. I checked them all with a vacuum pump when I rebuilt the box. They all hold vacuum. I know there is a check valve on the vacuum harness attached to the heater controls. I will swap that out and see if it helps. I probably should have done that before installing one near the engine. It's definitely not the compressor kicking off. Like someone else already posted, it's not connected to the throttle so the compressor has no idea I am accelerating. Not to mention I have cold air constantly coming from the drivers vent. I am positive it's a vacuum issue. I just have to figure out what's causing the issue and figure out how to fix it. Once it starts getting hot I will be miserable if it blows warm every time I accelerate. Also, do they make blower motors with more power? Mine blows air OK but nowhere near what a newer car does...I know...It's 40 year old technology...It would be nice to have it blow out more air...I'm just saying...

Posted By: RapidRobert

Re: AC goes warm on acceleration - 04/19/14 10:36 PM

if the blower motor is recieving full 12V on high then I think a modern motor that spins at a higher RPM would be the solution. shouldn't be too hard to find one of the right dimentions & swap the round vane piece onto the shaft with a setscrew. I'd think it'd be just like a box fan in your shop. the faster it turns the blades the more air it kicks out

Posted By: Telvis

Re: AC goes warm on acceleration - 04/20/14 03:17 AM

Weird thing happened today. Took that car out and thrashed it quite a bid. The air stated cold! Never had an issue.

Posted By: RapidRobert

Re: AC goes warm on acceleration - 04/20/14 03:49 AM

Part time problems are the cats' ass

Posted By: therocks

Re: AC goes warm on acceleration - 04/20/14 02:33 PM

Most had a vacuum resevoir.It retaind vacuum on heavy accel so the unit had vacuum.There should be one somewhere.Make sure its holding vacuum if you have one.Most were round plastic some like Fords actually had a tin can that was painted.Rocky

Posted By: Telvis

Re: AC goes warm on acceleration - 04/20/14 04:06 PM

I don't think the E bodies had them. I had a 68 Charger that had the canisters. I thought that was for the headlight covers. If my Challenger has one it's hidden somewhere inaccessible because I have had everything apart at one point or another.

Posted By: moretoys

Re: AC goes warm on acceleration - 04/20/14 04:08 PM

isn't the temperature door,cable operated? the vacuum controls the mode,direction of the air flow. the system could be undercharged or overcharged. (ambient temp will cause this to do different things)The system should also shut off too prevent freeze-up. There would be a switch on the carb if it is equipped with a.c. throttle cut out switch.or could have a switch inline with a vacuum line.

Posted By: cjskotni

Re: AC goes warm on acceleration - 04/20/14 08:43 PM

Quote:

isn't the temperature door,cable operated? the vacuum controls the mode,direction of the air flow. the system could be undercharged or overcharged. (ambient temp will cause this to do different things)The system should also shut off too prevent freeze-up. There would be a switch on the carb if it is equipped with a.c. throttle cut out switch.or could have a switch inline with a vacuum line.

I am not sure about the 73 E-bodies but the 71-74 B-bodies, all the doors inside the HVAC box are vacuum actuated. The only thing that is cable operated on the 73/74 B-body is the heater valve inside the engine compartment. Earlier years are vacuum here as well.

If he is running the original compressor, they had a valve (big honken canister looking thing) on the AC lines that would serve the purpose of not allowing the evaporator to freeze up. If you go to a Sanden compressor, you will need a separate thermal switch to do this.

With a factory 73 B-body setup, the only thing (besides turning it off) that can cycle the compressor is the low pressure switch on the drier. If you look at the wiring diagram, the AC compressor circuit comes from the HVAC controls to the low pressure switch then directly to the compressor. There is no connection whatsoever to the accel linkage or carb. I can't imagine the E-body would be any different.

Trace that blue compressor wire....I bet you will see it goes to the low pressure switch on the drier and then goes with the engine harness back to the firewall bulkhead connector. From there, it's straight to the HVAC head unit. Not anything else that should break this circuit....

Also FWIW, 73 B-body didn't get any vacuum canister I'm aware of. I know mine never had one. Maybe somebody can chime in but I am thinking the E-body would be pretty much the same. These engines from the factory pulled plenty of vacuum on their own in 73...

Posted By: Telvis

Re: AC goes warm on acceleration - 04/21/14 03:05 AM

The AC system is working properly. I converted to a sander system from Buchillon Performance. The issue is in the heater box. It is vacuum controlled for all doors. The only cable runs to the heater diverter valve and is operating properly. I swapped out the one way valve for the vacuum under the dash. Drove it a bunch today and it about froze me out. I think I am good at the moment. FYI... There's no AC cutoff at the throttle.