AC shuts off when on the gas pedal

[Fiorano]

This part weekend I drove my car from VA to Montreal for the Formula 1 race. Anyone who hasn't gone, should sometime. Anyway, while driving up and back from Montreal, the cars AC would either decrease in intensity or completely shut off during whenever I needed to give the car gas. Any ideas on the problem?

Thanks.

 

[Shelby3]

It is supposed to work that way.

 

[01sapphireGTS]

I attended that race several years ago, loved it. There is nothing like F1 !

The A/C is supposed to taper off or shut off during acceleration. I forget if it's a computer controlled thing or a vacume controlled thing. In some cars the loss of manifold vacume results in the vacume operated vents closing. Many manufactures have the A/C disengage during "acceleration" for added passing power, thinking they are doing you a favor (which in many cras, they are).

I don't think you actually have a "problem".

 

[John ACR]

Fiorano,
Normal A/C operation.
No problem.

 

[luc]

Re: AC/Fan turns off when stepping on gas?
#392719 - 04/08/04 10:12 AM Edit Reply Quote Quick Reply



lot of mis-informations in this thread:

1/ the fan doesn't stop blowing (hot or cold) at WOT.

2/ The A/C clutch dis-engage at WOT.

3/ The A/C clutch is not responsible for hot air at WOT.

4/ The problem is vacuum related(lack of it) at WOT.

The reason:

At WOT, the engine vaccum get very low and all the valves/doors in the heater/A/C system are vaccum operated and the door controling the cold (A/c) air simply close.
result being a lack of cold,forced air through the vents.


The Solution(s)

1/ a one way check-valve on the A/C heater vaccum line coming from the engine at the side of the valve cover on the passenger side.

2/A combination vaccum reservoir/check-valve (part# 53003408,less than $15) on the same line.

Luc.00GTS

 

[Motor City Mad Man]

Sell the car. But seriously as mentioned above it was designed to do this so you have all the power the car was meant to have at WOT.

 

[Fiorano]

Thanks for all the replys. I can't believe I didn't notice it before. Anyway, it is good to know nothing is wring with the car.

 

[Randy]

It is supposed to work that way.

No, ITS *NOT* SUPPOSED TO WORK THIS WAY. Reference Herb Helbig's comment on it in a past Viper Mag query (right before his normal litany of "take it to the dealer"). Otherwise, why would the AC clutch stay on??

Admittedly, every Viper I've owned or driven/ridden in has had this problem, but its the fault of either a bad design (missing vaccuum check valve) or bad part (defective/failed vaccuum check valve). Herb indicated there is a check valve somewhere behind the A/C controls, but I've never found it in either of the Vipers I owned. A missing/defective valve lets vacuum pressure bleed off during the low vaccuum of an open throttle, and the ventilation system doors fall back to their rest position; i.e., no air past the cooling coils. Yet, the A/C compressor does stay on.

The fix is pretty simple - just put a $5 check valve on the vacuum line coming from the right intake bank before it goes into the firewall. Its the very thin fairly hard plastic tube. The check-valve I used was suggested by a Chrysler parts person, it has part number #1-045677204 on the side, and was something like $5 plus tax. I used a short piece of normal vaccuum hose to connect it to the intake (with two small hose clamps), and put the existing hose into it, then zip-tied it to the heater hoses.

Ever since, its worked like a champ, no lack of A/C under throttle.

Its amazing how many people think this problem is designed this way, but haven't noticed that the A/C compressor clutch is still engaged, and thus should make you wonder *why*.

 

[Johann]

I agree with luc, I find nothing in the service manual description of operation or wiring diagrams that remotely suggests that the compressor clutch releases at WOT; the so called "normal" condition is a result of low vacuum at WOT and isn't normal at all.

 

[DarcShadow]

I realize this is an old thread but with it getting hotter again I've decided I want to fix my AC so it doesn't blow hot air at WOT. Was just wondering if any one has a good step by step procedure, preferably with some pictures. If so I think this would be a very good think to have added to the HowTo section of this web page, or at the very least send me a copy.

 

[Randy]

I realize this is an old thread but with it getting hotter again I've decided I want to fix my AC so it doesn't blow hot air at WOT. Was just wondering if any one has a good step by step procedure, preferably with some pictures.

Take a look at the passenger side intake rail, and the small tube coming off the right edge of it, something like 4-6" from the firewall end of the intake. The tube comes off easily (and, for some reason, it fell off both times I've spun on the track - haven't quite figured that one out).

That is the vacuum pickup for the HVAC system. Either go down to your friendly mopar parts place and buy the part number I mention above, or just ask any parts supplier for a "vacuum check valve", and put it on that line between the firewall and the engine air intake tap. If in doubt as to which end goes where, **** on each end, and whichever end doesn't allow you to **** air through it goes on the tube that goes into the firewall.

You don't need to cut anything to do this, as the tube just pulls out (and can be easily re-inserted) into the air intake, so this is a zero-risk modification.

 

[Matt M PA]

At least on my GTS, it isn't blowing hot air...it is redirecting the cold air out the defroster vents. Obviously a vacuum issue.

 

[01sapphireGTS]

Luc & Randy: Thanks for knowing that. I will make the mod to my car as soon as I can walk again (ankle injury) and post results. I do know that some GM vehicles used to (maybe still do) program the PCM to disengage the A/C Clutch at WOT. Of course the small girly GM engines need the "help" haha.

 

[DarcShadow]

Installed the new check valve today and it works like a champ. The part number above didn't show up in the computer but they found a $5 valve that works just great. They also said they sell a lot of them, mostly for trucks.

So I've got another question now. I understand the basic idea behind the vacuum door thing and the check valve only allowing air to pass one way. But does the valve actually prevent air flow or just greatly slow it down so you don't notice a sudden loose of vacuum? Cause it seems to me if the vacuum stayed how would you ever open the vent doors and have them bring in outside air?

 

[Randy]

Installed the new check valve today and it works like a champ. The part number above didn't show up in the computer but they found a $5 valve that works just great.

I wondered if the part number on the side of the part had any reference in their system - sorry about the dead-end on that.

So I've got another question now. I understand the basic idea behind the vacuum door thing and the check valve only allowing air to pass one way. But does the valve actually prevent air flow or just greatly slow it down so you don't notice a sudden loose of vacuum? Cause it seems to me if the vacuum stayed how would you ever open the vent doors and have them bring in outside air?

I don't know the immediate answer to that one - but you could perform a leak down test on it to determine how long it will hold the vaccuum. But, I would imagine that the way the vent doors open is that other switch position does indeed vent outside air into the lines, allowing them to change back to rest.

 

[luc]

Darkshadow:

The answer is very simple:

All the valves/flaps are actuated by vaccum motors,the one we are talking about is open with vaccum and closed with no vaccum.

When you put a check valve,even at WOT,the vaccum stay in the lines/vaccum motors and allow the valve to stay open,so basically it's a 1 way door that restrict flow 100% in on direction.

At the back of the heater/AC panel,just behind the "position" dial there is a rubber plug with 3 or 4 hard plastic lines and 1 "dump" vent,1 coming from the vacuum source (the engine) and the other ones going to the valves/flap.

When you move the rotary dial to a position that require a vacuum motor to "loose" vaccum in order to change the position of the valve controlled by this motor,2 things happen:

The vaccum source to the hard plastic line going to this motor is blocked and this same line is "connected" to the vent/dump source in the switch,allowing the motor to loose it's vaccum.

Luc 00GTS

 

[DarcShadow]

Thanks for the info. I should of relaized there'd a second valve that dumped the vacuum. Thanks for the info though, always nice to get a better understanding of how things work.

 

[AJT]

Installed the new check valve today and it works like a champ. The part number above didn't show up in the computer but they found a $5 valve that works just great. They also said they sell a lot of them, mostly for trucks.

So I've got another question now. I understand the basic idea behind the vacuum door thing and the check valve only allowing air to pass one way. But does the valve actually prevent air flow or just greatly slow it down so you don't notice a sudden loose of vacuum? Cause it seems to me if the vacuum stayed how would you ever open the vent doors and have them bring in outside air?

What part number did you end up getting??

Did anyone ever give a final fact on whether the clutch disengages at WOT, or is it all vaccum related?

Thansk
Andy

 

[99GTSACR]

The reason is in the one way check valve behind the radio is too small and has no way of holding a vacuum enough to hold the doors. Replace the valve with a check valve from a Dakota and it will not do it any more. At wide open throttle the vacuum drops to zero or near that and vacuum is what keeps the blend door in the position for the vents...defrost is the default position. The Dakota valve is a little bigger and has a small tank built in order to hold a small vacuum but it does solves that problem. Just pull the radio and behind the a/c head on the tunnel the is a small black valve in line to the a/c controller...that is what you need to swap with the revised part. Make sure you install it in the right direction...just as you removed the old one. The new valve will have a green dot on the side that connects to the shortest hose. I would recommend remembering how you removed the original one by simply blowing through it to tell the direction of installation for the new valve. The vacuum can only go through the valve one way. Also the new valve comes with a 90-degree elbow; just disregard this, as it is not needed. The ends on the new valve are a little larger then the original however it will slide on the old hoses and you won't have to worry about them falling off.

The part number is: Mopar Part 1-04677204

Jeff

 

[luc]

I'm sure than the A/C clutch dis-engage at WOT but, that's not the reason for the vent problem

The clutch cycle all the time under the control of the low pressure cycling clutch switch and you don't loose airflow to the vents.

No,why am I sure that the clutch dis-engage at WOT?

The service manual explanation of the clutch is as follow:

...the compressor clutch engagement is controlled by several compoments.....by the Powertain control Module...

Now, looking at the PCM output, at connector C3,cavity 1, we have in the PCM operation, a feed,called, "A/C compressor clutch relay control", to the "Air Conditionning WOT Relay"

Obviously a relay is an electrical device used to turn a circuit on and off and since a relay has only those 2 functions,either the A/C is ONLY on at WOT or ONLY off at WOT.

What do you think it is?

Luc.00GTS

 

[AJT]

Just pull the radio and behind the a/c head on the tunnel the is a small black valve in line to the a/c controller...that is what you need to swap with the revised part.

I thought the valve was between the valve cover & firewall?

So your saying pull the trim & radio out & its behind the AC controller. Sounds easy enough. Thanks for the part #.


Andy

 

[luc]

You can do it either way since we are talking about the same black vaccum line but it's a lot easier to put it on the engine side since (at least on my 00) to remove the A/C controler,you need to pull the dash out to access the screws holding it and I don't think that you can reach the valve by the top if you remove the radio.

Luc.00GTS

 

[AJT]

Thanks

I'll look tonight & see if I can find the line under the hood.

Passenger side right?

Andy

 

[luc]

Yes, on the side at the back of the valve cover.
You will see a rubber 90* elbow with a hard plastic line in it.

Luc.00GTS

 

[Johann]

I'm sure than the A/C clutch dis-engage at WOT

No,why am I sure that the clutch dis-engage at WOT?

The service manual explanation of the clutch is as follow:

...the compressor clutch engagement is controlled by several compoments.....by the Powertain control Module...

Now, looking at the PCM output, at connector C3,cavity 1, we have in the PCM operation, a feed,called, "A/C compressor clutch relay control", to the "Air Conditionning WOT Relay"

Obviously a relay is an electrical device used to turn a circuit on and off and since a relay has only those 2 functions,either the A/C is ONLY on at WOT or ONLY off at WOT.

What do you think it is?

Luc.00GTS

What year manual are you using as a reference? The '97 manual shows pin #1 in PCM connector C3 as an ignition coil driver.

None of the pins on the '97 PCM are labeled "Air Conditionning WOT Relay".

While some PCM pins are labeled A/C control there is no reference to WOT disconnect in the operational text. Obviously this must vary from year-to-year.

 

[99GTSACR]

You only have to pull the Radio and reach behind the AC control. It takes 5 Minutes to do the job. This is the correct way to repair this problem since you are not only replacing the small check valve with a large check valve / Vacuum Tank but you are putting it where their is no heat to damage the plastic valve (Thats the original location). The recall for Dakota trucks repaired the same problem this way.

 

[luc]

johann:

I'm using the 2000 service manual.

They could have moved the pins around but I'm pretty sure the A/C work the same.

Try to look at the pin-out diagrams for all the connectors

Luc.

 

[99GTSACR]

The clutch may disengage however that will not give you instant air change, which is the problem, described here.

 

[luc]

99gtsacr:

you're right, if you can acces the valve through the radio cavity,it's better to do it there.

On my car, I used a different system,instead of a 1 way valve,I used a combination vaccum reservoir/valve (Jeep/DC part # 53 00 34 08) it's a black plasic ball about 3" in diameter that I mounted under the windshield wiper washer bottle.
This way,even with the engine off you can cycle (and hear) all the valves/flaps 5 or 6 times.

Luc.00GTS

 

[jrkermode]

Parts from Mcmaster.com
High Temp Valve #47245K26, $4.80
High Temp Hose, #51135K172, $.81/ft (need 1.25")