Automotive Air Conditioning Information Forum (Archives)

qws on Sat August 04, 2012 9:15 PM

Year: 84
Make: chevy
Model: corvette
Engine Size: 388
Refrigerant Type: 134a

Hi guys, glad I found this forum.
I just went thru my AC on a 84 corvette.
New parts: orfice,condensor,compressor,accumulator, 134a
Vac'd the system for 45 min's, leaked checked,and filled. Spec for the 84 is 2.8 lbs. Using a 80% conversion for the 134a they filled it with 2.2 lbs. The compressor was brand new and had oil already in it. I'm assuming they accomadated for this in the conversion.

Anyways here's my problem:
Start the car and turn the AC to max- blows very cold!..woohoo!
Put the car into gear and it stalls. i noticed that when i turn the ac on my steering rack grinds a bit... brake pedal is weak.
I've done some datalogging on it to see if I noticed anything unusual and didn't. I put a vac gauge on my intake.
Idle with no AC its 14
Idle with AC its 12
Idle,In gear,AC on its 8

Can I assume I have a compressor problem?
Maybe overcharged?
thank you for reading

fonebone on Sun August 05, 2012 1:26 AM

Hi qws- You have a 388 cube eng.? How radical a cam in it? Now- with no AC on, does it stall going into gear? With cold AC, and the amount you put in it, you are doing fine as far as charge is concerned. With those real low vac numbers, if your cam is not super radical,you have a bad vac leak somewhere. Weak brakes? Do you mean a lot of pedal effort and no stopping power? If so, and being an older '84, I'd look for a bad brake booster diaphragm leak, or the hose running to it causing a massive drop in vacuum. . Those are real low vac numbers for any car! I do not see any connection between the AC and your other troubles. It's just adding to the load on the engine when you drop it gear.

qws on Sun August 05, 2012 8:04 AM

qws on Sun August 05, 2012 8:10 AM

Hello, thanks for a reply.
the cam is 230/236. My normal vac number using my analog gauge has always been 14hg. Brakes have also were fined with no problems.

My assumption was that since I saw the vac numbers go real low when the AC is on, along with a steering rack that would begin to grind when turn the wheels, and the brakes then having the feeling of low vac when applied would be due to a sluggish compressor.

Those symptoms above are only present when turning the AC on. It only stalls about 30 seconds after putting it into gear... if I tap the gas pedal I can keep it running.

fonebone on Sun August 05, 2012 4:33 PM

Hi qws- Still feel we are dealing with a vacuum leak somewhere. I assume we're dealing with an automatic tranny.when you "put it in gear"? Because of age, I'd check all vac lines-spark advance, the modulator line down to the tranny to the mod valve, and the mod valve itself, from intake down, brake booster line, check valve that is in the line. You also have a vacuum line running into the cowl to operate the heater/ac control. There is a vac control switch there that can wear out, causing slow operation of mode doors directing air flow, but would not draw so much vac to effect idle. What is your idle RPM? Working with a modified eng., your initial spark advance could be too low. Try upping the spark advance a couple of degrees at a time and see if that helps. Of course, we can't go too far here, but I don't know what your initial adv is. Not sure what is meant by "steering rack" noise. You should have a conventional recirculating ball steering power steering setup. They can make a variety of noises-low fluid, hard cranked over to one side squeal,etc. The very low RPM before stall could cause some weird noise. With an engine that big, with all that torque, it should handle the load ok, but at low idle with parasitic loads of an automatic tranny, ac pump, alternator, you aren't making much power.

bohica2xo on Sun August 05, 2012 6:40 PM

Not enough information for a diagnosis.

Are you running the OEM fuel injection? Aftermarket carburetor? Ignition system?

The A/C load is not the problem.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

qws on Sun August 05, 2012 11:20 PM

I certainly appreciate the replies.
Let me give you somemore information about the car
388 roller with the cam specs I'd given above
Intake is a Holley Stealth Ram (fuel injected) and driven with dynamicefi's ebl/flash ecm.
Tranny is a 700r4 that has been specifically built for this engine.
Base Timing is set to 6*BTDC

My normal vac has always been 14-15hg
(on a side note.. my buddy has a 86 with practically the identical engine and trans, he uses a superam with a slightly milder cam. His normal vac is 17hg. He has no problem when turning his AC on)

I have no problem going thru my vac again.... I disconnected every vac hose but left my map sensor in place.. Direct from the intake I have 14hg...should I continue to test the rest of the vac lines?

My definetion of the steering rack of it grinding..would be the same sound as if I didn't have enough oil in it. My brakes feel as if I lost the vac to the booster.. hence the 8hg I get when I turn on the AC. These symptoms go away if I turn the AC off.
My thought is the compressor for whatever reason is turning so hard it putting a strand on the serpentine belt ..and in turn effecting steering,voltage,slower rpm causing such a low vac.

I think my plan at this point is to take the car back to where they filled it and get the actual reading of the lo and hi side along with ambient temperature to confirm its not overfilled.
I'm also thinking of looking in my .bin to see if the IAC counts need to be adjusted.
Am I going in the right direction?

Edited: Sun August 05, 2012 at 11:27 PM by qws

bohica2xo on Mon August 06, 2012 1:40 AM

Save yourself a trip on the A/C

There were at least two versions of emissions equipment on that vehicle. Your buddy may have the "same" car - and yet not.

Depending on several things, it may have a simple 4 wire distributor module - or the 6 wire setup with ECM spark control.

The first thing to do however is correct the IAC offset & TPS adjustment. With any sort of mods on that old OBD I stuff, it is important to adjust the throttle plate angle for maximum IAC authority. You should not be seeing any drop in RPM with the A/C on.

It is simple to do. With the engine at operating temperature, make sure the A/C & the headlights are off. Use a good idle tachometer, and slowly increase the throttle blade opening on the idling engine. If you take a 1/4 turn on the adjustment screw, you should see the idle rise - then drop back to the ECM setpoint. Take 1/4 turns, until the speed does NOT drop. Then back up 1/4 turn. This puts the IAC at the lowest opening - giving it much more range to add throttle when cold, or when the A/C is on. Once that is done, shut the engine off & re-adjust the TPS to the factory spec.

The OEM setting for the IAC was designed to give it the capacity to cover up a vacuum leak & keep the engine in smog limits. If you develop a vacuum leak that has you idling @ 1500 rpm, you will probably notice it. The OEM setting left the IAC with less than 50% of it's travel to manage idle speed.

If that has no effect, then check the IAC air path for blockages & the IAC for operation.

It is not the A/C.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

qws on Mon August 06, 2012 9:25 AM

I have the 6 wire with ecm controlling my SA

I will try this and report back.

qws on Mon August 06, 2012 10:51 AM

I have a question after reading your directions

I'm understanding this as:
On a warm engine adjust the blade screw using 1/4 turns to see the idle rise
Once I see that adjust it back to where the ecm is calling for my idle/park which is 850
Then I adjusted my idle down to the point where it can't go any lower

Is this correct?
And would I do this with the IAC connected or not?
thanks


Edited: Mon August 06, 2012 at 10:54 AM by qws

bohica2xo on Mon August 06, 2012 11:30 AM

Ok, so you have the ECM control on the spark advance. Since the ECM is no longer stock, check to see that it is really getting enough advance with a timing light. If you don't have enough initial timing, power available at idle drops way off.

For setting the throttle blades:

Engine warm & idling.

IAC connected & working.

No additional loads.


You want to increase the throttle plate opening in increments while letting the ECM reduce the idle to spec by closing the IAC. As you continue to open the plates, you will reach a point where the IAC is completely closed, and can no longer reduce the idle to spec. Back up 1/4 turn when that happens.

This leaves the IAC almost closed. That way it can open up to feed the engine & maintain idle when the additional 6 horsepower from the A/C compressor hits. It also helps cold drive off, lock-to-lock steering at idle in gear, etc.




B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

qws on Mon August 06, 2012 3:32 PM

Here is where I'm at.
Checked my SA with a timing light vs ecm. Idle 25-30, Idle AC on 25-30 and the same with it in gear until it dies.

Then moved onto my IAC adjustment. Followed the directions to a tee. Turn car off.. started IAC steps are at 16 at idle. Turn on AC and put it into gear and it stalled

Then went thru TPS adjustments it was .56 and readjusted to .545 (OEM spec).. started the car... same thing. Dies when it goes into gear.

Each procedure was datalog an is in .csv format if you would like to see the adjusting of the IAC vs RPM.

What do I do next?
thanks

qws on Mon August 06, 2012 8:38 PM

Let me throw some more information to make this more confusing.
Hooked up my pressure gauge to the plenum. The only other connections were the fpr,map sensor,pcv. I disconnected the power brake booster,cruise servo,and the lines that feed the ac control board.

Started the car, I was able to turn on the AC, put it in drive and it didn't stall???
How was my AC able to turn on with those vac lines disconnected? Is this telling me I have a vac issue and maybe a vac pump would solve my problem?

Edit.. I need to do one more thing to confirm this

Edited: Tue August 07, 2012 at 1:05 AM by qws

qws on Tue August 07, 2012 9:41 AM

The post above this can be ignored. It did continue to stall when I removed the vac lines. So I don't think its a vac issue.
Is it time to pull the compressor?

qws on Tue August 07, 2012 2:33 PM

Removed the TB and completely cleaned all passages including the IAC passages. Installed a New IAC, same problem is happening.
Is this looking more like a AC problem?

bohica2xo on Wed August 08, 2012 1:47 AM

Looks like your tune is not too bad. IAC @ 16 steps puts it nearly closed - a good thing.

Plenty of timing at idle - a lot in fact. It has been a few years since I hacked the old OBD1, but if it is not hard to crank then that is probably ok.

How is it to drive with the A/C off & everything connected? No stumbles, tip-in bog or spark knock? No bad habits? Lock to Lock with the steering, stopped idling in gear ok?

I have seen a few bad compressors. Usually when they fail they will stall a healthy engine or make the belt smoke. Cooling well & simply drawing too much power is not something I would expect from a bad compressor. Can you turn the clutch plate on the front of the compressor (engine stopped!) by hand?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

qws on Wed August 08, 2012 12:15 PM

haha... your on TGO as well!
No bad habits but I will take the car again today out to do somemore datalogging and give some more feedback.

Edited: Wed August 08, 2012 at 12:17 PM by qws

bohica2xo on Wed August 08, 2012 2:43 PM

Stock timing was like 9 degrees. Hard to say anything is wrong with the "20" you re reporting if it runs ok. Seen enough slipped dampers to discount timing in the big picture...

Was this one of those cars with two TBI units?

If memory serves, pin 21 on the ECM fed the A/C control. Idle up should have been part of the ECM function.


Uh "TGO"? I missed that one.

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

qws on Wed August 08, 2012 3:08 PM

My bad.. I thought you had seen the datalog I posted on thirdgen.org (TGO), forgot I posted my IAC counts here.
Yes this was orginally a crossfire. Dynamicefis ecm is a plug and play unit that just gets exchanged for my orginal ECM. No wiring changes except I used one wire that went to my air divertor for the IAT sensor. So its now a speed density set up. The new ecm and its software are nice. I have a dash/datalog program and it just flashes the tune in. No chip burning,etc.

I was looking at my tune and I bumped up the IAC-Idle/Drive RPM by 50 rpm. Right now as it stands I've been able to keep it running while in drive. Of course now I'm running rich in those cells so I have to make a few adjustments to the tune. I'm gonna run the car later today (hopefully) to do another log. At that time I will also be trying out the AC.

bohica2xo on Wed August 08, 2012 3:21 PM

Ok, so did your manifold swap change the TBI to a single?

The original system had two IAC units - that is a lot of compensation path.

I would look at adding an air bypass solenoid valve connected to the compressor clutch circuit. Speed density system will never know the difference.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

qws on Wed August 08, 2012 5:24 PM

I went from two TBI units to the holley stealth ram, which has 8 injectors, its more like a TPI style, just a lot better.
Yes it had two IACs,and now I only have 1.

What are the benefits of having a bypass solenoid on the compressor cluth?

qws on Mon August 13, 2012 3:04 PM

After I bumped up the idle/drive it seemed to work ok. this past weekend I installed a vac pump that runs the brake booster and AC controls, now I'm back to stalling when in drive. Could I be hitting a low spot in the cam causing it to stall out?

qws on Tue August 14, 2012 10:20 AM

Can I use a normal AMP probe on the AC compressor?

bohica2xo on Thu August 16, 2012 2:54 AM

When you went to a single IAC, you gave up a lot of idle airflow. The ECM is configured to drive both IAC's in the original system in parallel.

Since it is still a speed density system, any air that goes in to the intake is the same. A huge vacuum leak or an open throttle plate is all the same to it. So by installing a small solenoid valve wired in parallel with the A/C clutch, you can provide a controlled air path in to the intake manifold. Usually does not take much. That way when the A/C clutch is engaged, the solenoid valve adds air below the throttle plates, and compensates idle speed directly.

The curb idle speed on that system is fairly low. Once it maxes out the IAC & falls 50 rpm below target - you are done. It will stumble & die. You say you can keep it running with the throttle - so allow the A/C to do just that with a bypass valve.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.