A/C cutoff switch?

[cuda6pak]

Just got the A/C recharged (worked fine before) and a new tranny and PTC 3200NL stall put in. I noticed on the freeway when the RPM's were up or I was in slight boost that the A/C would cutoff and start blowing hot air.

Do GN's have some sort of WOT-like cutoff switch for the A/C? I'd like to be able to run consistent cold air while on the interstate or driving around in town. Obviously if I'm racing I'll shut the A/C off myself.

 

[DailyDrifter]

Just got the A/C recharged (worked fine before) and a new tranny and PTC 3200NL stall put in. I noticed on the freeway when the RPM's were up or I was in slight boost that the A/C would cutoff and start blowing hot air.

Do GN's have some sort of WOT-like cutoff switch for the A/C? I'd like to be able to run consistent cold air while on the interstate or driving around in town. Obviously if I'm racing I'll shut the A/C off myself.

I think you answered your own question. Most cars will kill the AC when you go WOT or near there.

 

[cuda6pak]

I think you answered your own question. Most cars will kill the AC when you go WOT or near there.

The thing is I wasn't even close to full throttle. I'm talking 1/4 throttle at MOST. It's just with the 3200 stall on an uphill part of the interstate that 1/8 throttle equates to 5psi of boost. Going from a stock D5 converter to a 3200 NL. I was just wondering if there was anyway to pull the power to that cutoff switch somehow, unless its somewhere in the ECM. Because when I'm just trying to maintain 75-80mph, I'm sitting right at 0-2 or 3 psi and then it cuts off and starts blowing hot air for 1-2 minutes. Which basically renders the A/C useless.

 

[DailyDrifter]

You might be able to rig a switch up, that way you can manually overide it. You can jump the terminals on the high psi switch on the dryer, that should cycle the a/c clutch on, then take it for a ride and see what it does.

 

[cuda6pak]

I thought that the high/low pressure cutoff switch only had to do with the system pressure of the refrigerant? Is there a separate switch that I'm not thinking of that cuts power to the compressor based on TPS voltage or MAP pressure?

 

[rodman99999]

I thought that the high/low pressure cutoff switch only had to do with the system pressure of the refrigerant? Is there a separate switch that I'm not thinking of that cuts power to the compressor based on TPS voltage or MAP pressure?

You're right about the pressure switch only being affected by refrigerant pressure. If the ECM determines the load of the engine needs to be reduced(such as under full thottle conditions) it will cut power to the AC Compressor Clutch via the AC Cut-Out Relay. You could put a bypass switch on that relay's (DK GRN/YEL) wire to ground, to overide the ECM(if you feel daring). See pages 8A-67-3, 4 and 15 of the GM manual. The AC Compressor(Cut-Out) relay is above the passenger side wheel well(it's the one farthest forward).

 

[cuda6pak]

You're right about the pressure switch only being affected by refrigerant pressure. If the ECM determines the load of the engine needs to be reduced(such as under full thottle conditions) it will cut power to the AC Compressor Clutch via the AC Cut-Out Relay. You could put a bypass switch on that relay's (DK GRN/YEL) wire to ground, to overide the ECM(if you feel daring). See pages 8A-67-3, 4 and 15 of the GM manual. The AC Compressor(Cut-Out) relay is above the passenger side wheel well(it's the one farthest forward).

Why would it cut out the AC compressor when I'm barely on the throttle at all? Is it because of the high stall building boost? Would it hurt to completely remove that relay?

 

[rodman99999]

Why would it cut out the AC compressor when I'm barely on the throttle at all? Is it because of the high stall building boost? Would it hurt to completely remove that relay?

Could be the stall, but apparently the ECM has a different opinion than you, with regards to the load the engine is seeing. If you remove the relay, you won't have any AC at all. The ECM grounds(completes the circuit) for the relay's solenoid coil, which closes the switch(in the relay) to supply power to the AC Clutch.

 

[87GN_70GS]

ECM relies on TPS to cut off compressor.

 

[49-blues]

FYI-the switch on the accumulator is a low pressure switch-not high.

 

[rodman99999]

Once again- If you want your AC clutch not to disengage under load(at your discretion): Splice a switch and wire to ground from the DK GRN/YEL wire on the AC Cut-Out Relay. If you want to eliminate the ECM's option to cut-out the AC altogether: Cut that wire and run it to ground from the relay.

 

[Just a Six??]

I thought that AC cut out when ECM saw 3.75 on TPS? Maybe the TPS is screwy as I have a 3800 stall & it doesn't do it to me.

 

[38turbo]

I thought that AC cut out when ECM saw 3.75 on TPS? Maybe the TPS is screwy as I have a 3800 stall & it doesn't do it to me.

+ 2 check tps and make sure your maf is showing good readings (maf also tells ecm engine load not sure if it will affect a/c request a chip expert might) the computer should do a good job of controling compressor cutout due to engine load and unless you driving around at wideopen throttle you shouldnt notice a decrease in a/c performance
my 2 cents

 

[dennisL]

The chip has a parameter for throttle position A/C disable which in the stock chip is set to 80%. Most custom chips I've seen have this reduced to about 70% and a few designed for street racing had it set to 50%. Any TPS below the threshold and the A/C stays on.

As far as A/C control goes, the ecm does not care if the boost is on or what the load is. It only checks the TPS threshold. By the way, the same parameter is checked when you turn the A/C on, only the ecm subtracts 6% (max TPS of 74% in stock chip).

Dennis

 

[scottyb]

You probably need to service your AC - low on refrigerant. Mine has done the same as yours - blows cold at idle or low speeds, than cycles during highway cruise.
When you are at highway speeds, your AC is working at peak efficiency - proper engine rpm, and strong airflow over the condenser core. what that adds up to is the low side pressure being too low and the low pressure switch cycles the compressor.

 

[bmackinnon]

Are you sure the AC clutch is actually disengaging?? Sounds to me like the air temp selector door is moving over to the default 'heat' position due to lack of vacuum.... check the vacuum line check valve going to the HVAC... I think it's the 3-way on the driver side by the rear of the plenum... shouldn't allow boost to get to the hvac controls.... if it does, the door goes to 'hot'.... :wink:

 

[cuda6pak]

Are you sure the AC clutch is actually disengaging?? Sounds to me like the air temp selector door is moving over to the default 'heat' position due to lack of vacuum.... check the vacuum line check valve going to the HVAC... I think it's the 3-way on the driver side by the rear of the plenum... shouldn't allow boost to get to the hvac controls.... if it does, the door goes to 'hot'.... :wink:

I'll have to check that. Thanks for the info.

As far as the TPS goes, it is adjusted correctly and seems to turn the A/C off at around 1.15

 

[scottyb]

Are you sure the AC clutch is actually disengaging?? Sounds to me like the air temp selector door is moving over to the default 'heat' position due to lack of vacuum.... check the vacuum line check valve going to the HVAC... I think it's the 3-way on the driver side by the rear of the plenum... shouldn't allow boost to get to the hvac controls.... if it does, the door goes to 'hot'.... :wink:

The blend door is manual and vacuum won't change temp (although I'm not sure on electronic climate control units). Lack of vacuum will more likely cause air to pass to the default floor and defrost vents instead of AC vents.

 

[scottyb]

I'll have to check that. Thanks for the info.

As far as the TPS goes, it is adjusted correctly and seems to turn the A/C off at around 1.15

This is strange. Is this 1.15 threshold repeatable? Is it possible that your chip cuts the compressor at this value?

 

[dennisL]

As far as the TPS goes, it is adjusted correctly and seems to turn the A/C off at around 1.15

1.15V equates to about 16% TPS. I can't believe any chip would have that low a number for the A/C cutout TPS threshold.