1997 Tahoe AC rapid cycling problem

[MarkD51]

Hello all, first post here.

1997 Tahoe LT (no rear AC) with 39.6K miles, I am the original owner.

Original Compressor developed seal leaks.

Ist replacement compressor, brand new Delphi from Oreillys, with new Drier-Accumulator, and Stock Orifice Tube (from them to attain full warrantee). Was properly evacuated, and charged with 2 lbs R134a, and PAG 150 Oil. No go, AC cycling on for 5-7 seconds, off for 10-12. From dead cold, to warmed up, no leaks)

Changed Low Pressure Switch at Accumulator, no change.

Start all over, new Delphi yanked, brought back to Oreillys, due to I thought it might be bad, seemed a bit noisey, and clutch Gap was only .013"

Got another Delphi under Warrantee, this one ran quieter, had a .020" Clutch Gap.
Went to Chevy Dealer, and this time got an AC/Delco Drier Accumulator, and again, another stock Orifice Tube (confirmed, and both were identical to original, so don't think that's the issue)

System was flushed, blown, AC Compressor Bench Primed and turned before fire up, evacuated, recharged again with first 2lbs refrigerant, then 2.2 lbs, and PAG 150. No changes. All Oil quantities in Compressor-Accumulator were properly adhered to, for a fresh system

Three Low Pressure Cycling Switches replaced, no change.

In the high 70's to low 80's, Vent Temps at Max Setting, is 44.5 F

Clutch Fan appears OK, no change from when vehicle is dead cold upon fire up, to fully warmed up, AC clutch stays kicked in for 5-6 seconds, then kicks out for 10-12.

Will stay on if Low Cycle Switch Plug is Jumpered.

Could there possibly be too much Oil in the system? The Condenser (stock) was not gravity drained.

All new valves in hoses, no leaks detected. But they are the original AC Hoses-Lines.

Or, is it possible controller on dash is bad? All appears to work properly, fan speeds, temp control, etc.

This one has me stumped! Please help folks, I'm at about $900 with this fix, and still no joy. Mark

 

[lesterl]

If jumping the low pressure switch keeps it on, then you dont have a dash control issue, sounds like you are low on freon. What are the pressures low and high side while it is running/ cycling?

Perhaps you have a plugged condenser?

Got the orifice tube in right direction?

How are your charging the unit?

 

[MarkD51]

If jumping the low pressure switch keeps it on, then you dont have a dash control issue, sounds like you are low on freon. What are the pressures low and high side while it is running/ cycling?

Perhaps you have a plugged condenser?

Got the orifice tube in right direction?

How are your charging the unit?

Hi, and thanks for responding.

I'm sorry but this is where I may be of little help to answer your questions.

The work was done by a certified mechanic, not myself. He was aware of the constant rapid cycling when I brought him the truck, in which the first replacement of AC Compressor was done by another mechanic.

While I watched him do the entire replacement of Compressor, Drier-Accumulator, Orifice Tube, Flush, blown, oil added, and evac, and fill, I have no memory of what numbers were on the low-high side while cycling.

I forget the brand but the machine he used was one of those large roll around cart machines, with guages, and digital readout of how much refrigerant was added.

The first day he put in 2 lbs, and I went back the day after, and he upped the refrigerant quantity to 2.2 lbs.

I'm not sure about a plugged condenser, but what I once read after this work was done, was that flushing, and blowing the system out does not fully evacuate-drain the condenser of Oil. That one tech claimed he had seen flush and blown condensers still containing up to 16 oz of oil in them.

That the only effective way to remove the oil from the Condenser, is to physicaly remove it, and gravity drain it. Does this sound feasible-correct?
That there could be a possibility of too much Oil?

In this scenario, and if this is a possible cause of the rapid cycling, would it still then be possible if the condenser is so overfilled with oil to still be able to charge the system with 2.2 lbs of refrigerant?

Oher thoughts coming to mind, the equipment used to evac, and charge was flawed.

The evac took a good 45 minutes to draw down, the refrigerant did have UV dye in it, no leaks at all detected.

Mark

 

[lesterl]

Quick and dirty way to test is to grab both lines comming out of evap. Should be about the same temp (cold), if one is cold the other is warm then you are low on freon. That is the redneck way I have seen some check when guages arent avail for charging.

As far as the condenser filled with oil causing your issues, I would hope a professional mechanic (btw I am glad you had a pro do this) would have taken care of that before evacuating and recharging the system (again).

On my stuff I evacuate for upwards of an hour before refill, the more time in vacume the more time the moisture and stuff will boil out of the system.

I am not a certified mechanic (grew up in a GM dealership, literally), but something doesnt sound right to me either......

 

[MarkD51]

Quick and dirty way to test is to grab both lines comming out of evap. Should be about the same temp (cold), if one is cold the other is warm then you are low on freon. That is the redneck way I have seen some check when guages arent avail for charging.

As far as the condenser filled with oil causing your issues, I would hope a professional mechanic (btw I am glad you had a pro do this) would have taken care of that before evacuating and recharging the system (again).

On my stuff I evacuate for upwards of an hour before refill, the more time in vacume the more time the moisture and stuff will boil out of the system.

I am not a certified mechanic (grew up in a GM dealership, literally), but something doesnt sound right to me either......

Hi Lester, and thank you again for your help, and advice. I'll do as you say, and check the lines at the evaporator.

The system was flushed from the evaporator line, and exited at the condenser, I watched it being done.

Then the system was evacuated via that large machine, and it digitally counts down the evacuation cycle, adds, or removes oil as it goes.

Sorry I'm not too versed, and wise about HVAC, I know just enough to get into trouble. Ive also read that one never truly can purge the AC lines going-coming to the Compressor, that there are inline "mufflers" in them?

Where I might wind up, and where I probably should've went in the first place was my local Chevy Dealer. I've later heard some bad about the Delphi Compressor, but this is supposed to be the OEM manufacturer, and I believe this is what was originally in the Tahoe?

They charge $142 for normal AC service, and I should perhaps let them check the system, and see what they say?

Funny, but the original Compressor in my Tahoe (Labeled AC-Delco) also had a "remanufactured" tag on it. That's what GM threw in a brand new $37K SUV from the factory.

Yes, they would've charged me through the nose on both parts, and labor, but perhaps that is worth the money, that one, the system wouldn't probably have this nagging problem, and two, if there was a problem, that work, and parts would be covered by a 12 month-12,000 warrantee no doubt.
Mark

 

[Grebbler]

Without pressure numbers I am afraid to even wade into this.

You are cycling yet have mid 40's at the dash.

Jumping the LP switch keeps the compressor running so the dash control is not switching it off nor the HP switch.

You've replaced the LP switch a bunch of times on who's advice? A gauge would have indicated a bad switch or not. What about the guy charging the system? Is he stumped, too, or just pushes the FILL button on his machine and sends you packing?

2.2lbs should be enough freon so why the cycling unless you got the cosmic bad luck of 3 bad switches.

If the line before the orifice is warm/hot and and the other side cold going into the firewall is cold that's okay. If the dryer is a lot colder than the firewall line then I would think overcharge or restriction in the evaporator. If the line between the condenser and the orifice is cool or lukewarm then that would point to under charge, blocked condenser or weak compressor.

Without gauges on it it's all guesswork.

If you lived near me I would look at it for the challenge and to thumb my nose in the general direction of 2 mechanics that seems to have left you dangling in the breeze.

 

[MarkD51]

Gentlemen, may I please ask a couple simple questions?

Let's assume we have a correctly working AC system in a 1997 Tahoe.

As I understand it, the AC Compressor is supposed to cycle, to prevent Evaporator Freeze-Up, correct? (But I assume staying kicked in for 5-6 seconds at 80F is not correct)

Does the ambient outside temps have a bearing on how long the compressor will stay kicked in?

In other words, will there be a difference in the length of time the compressor stays engaged-operating, when outside temps are 80F degrees, or when outside temps are 98F degrees? Or no?

 

[lesterl]

If you have a good enough supply of warm/hot air across the Evap coil then it wont freeze up AFAIK, my compressors pretty much run a large portion of the time when I have the blower turned up. I think I only used 3 cans on my 95, I know the systems are a little different.

I'm with Grebbler, wish you were closer so we could help ya out in person and kinda thumb our noses at those mechanics. I am essentially shade tree myself, been doing my own service for some number of years, yet I could tell you what was happening by reading my guages.

Sounds like Grebbler has alot of experience with this.... I would listen to him...

 

[MarkD51]

Thanks again Lester,

This is one of three nagging problems I have with my Tahoe

The other, which recently surfaced on my last trip for the A/C repair, is a hard brake pedal.

The first 3 inches of travel are hard, my brakes otherwise work fine, both stopping power (with more effort), and the ABS system seems OK.

I have Stillen Statix Calipers up front, larger Units, which use 3/4 ton Pads, Ceramic Pads, Slotted Rotors, and Braided Teflon Hoses (3) on board.

Those were installed by myself about 10 years ago, and have worked perfectly up till now, and were much better than stock.

I might need a Booster, or I might just need a good thorough Power Bleed? I did a one man bleed last week, to no avail.

The other nagging issue, is I cannot use my Deltran Battery Tender, in conjunction with my Viper 5701 Alarm System. The Battery Tender trips the Alarm after 30 seconds of arming it, thus the only way I can maintain my Battery (Optima Yellow Top) is by placing the Alarm in Valet Mode.

In other words, my $550 Alarm, installed about a year ago, is basically useless.

Deltran, and Viper Don't have a clue why this happens?

Without the battery tender, the battery is dead within two week's time.

As for the AC, I might have to spring the $142 initial cost at the Chevy Dealer. It wouldn't bother me a bit, if that $142 solved my problems, but I am well aware that could turn out to again being a drop in the bucket, with Chevy saying you need this, and need that, and will charge me out the whazoo for parts, and labor that I actually didn't need.
Mark

 

[Grebbler]

You sure get some stumpers...

On the A/C. Yes it will run longer in hotter weather just to satisfy the temp control asking for more cooling. Humidity, vehicle speed, condenser air flow, etc all effect how freon will behave throughout the system. The deicing protection is usually done by the LP switch as the most common reason for evap icing is low freon. The A/C in that truck should be controlled by the VCM module some schematics show a third cycling switch. But the fact that when you jumper the LP switch and it stays running says to me that the module and other switches are working. The LP switch normally trips out around 25 PSI and lower. A working A/C can be that low in cooler weather and the tripping is normal since a lot of cooling is not called for, anyway.

Some off the wall things to check: Make sure the A/C belt is routed correctly, tight, and not worn or glazed. The old compressor could have worn out the belt tensioner. My '02 A/C has a separate belt and tensioner and that is a common issue. A slipping belt will cause cycles of pressure drop and LP tripping. Check the LP switch plug and ware harness. The LP switch will have clear groves on the spades if the connectors are tight. Jumper the plug and move the harness around and see if the clutch cycles. You may have a break in a wire that gets a better connection when you have it off the switch. The freon may still be low. A weak o-ring or seal could leak down to a certain pressure until it's able to hold - like when tires will have slow leaks that stop at 25 PSI but won't hold 35 PSI.

By far the simplest is to take it back to the person that charged the system, since you already paid and it's not working, and have him put on a regular set of gauges (not his charge machine since that's in question at this point) and see if the pressure is really dropping low enough to trip the LP switch or is it an electrical problem. He should do it for free to satisfy curiosity and defend his work. Make you he lets you watch to confirm what he says.

Brakes - You say they have been fine until now with the same components. Air in the lines or bad master cylinder would give you a softer pedal. Stuck ABS parts or a weak booster would make a hard pedal so make sure the vacuum line to the booster didn't get kinked or damaged when all his A/C work was done. Have someone apply the breaks with the truck running while you listen around the booster. If you hear a lot of air whooshing then the booster is the likely culprit.

Battery - I am not familiar with Optima. Is that an AGM battery? I can't see any car battery having a high self-discharge rate or any need for a tender. I would do a parasitic load test to find why the battery is dying. You can do it with any test meter that has a 10 AMP setting. In most cases the cause is a piece of audio equipment not shutting off or a door switch.

Anything can be fixed if the right people work on it.

Keep plugging away.

 

[lesterl]

To test the parasitic draw, pull the positive lead off the battery and install a testlight between the battery+ and the cable, the light will light, you can unhook devices and/ or pull fuses untill the light dims, probably wont go out totally, but when you find a circuit with a high draw it will dim down alot on ya.

Another way to keep batteries topped off with alarm is a solar panel in the dash, they make a nice 1'x 4" solar panel with a cig lighter cord that you can plug in and keep the battery fresh, that is what I do when I put a vehicle out of service for a while.

I agree on the weak booster or you could have some collapsed lines also...

I dont like the Optimas.... seen too many have to go back.... could be bad.

 

[MarkD51]

You sure get some stumpers...

On the A/C. Yes it will run longer in hotter weather just to satisfy the temp control asking for more cooling. Humidity, vehicle speed, condenser air flow, etc all effect how freon will behave throughout the system. The deicing protection is usually done by the LP switch as the most common reason for evap icing is low freon. The A/C in that truck should be controlled by the VCM module some schematics show a third cycling switch. But the fact that when you jumper the LP switch and it stays running says to me that the module and other switches are working. The LP switch normally trips out around 25 PSI and lower. A working A/C can be that low in cooler weather and the tripping is normal since a lot of cooling is not called for, anyway.

Some off the wall things to check: Make sure the A/C belt is routed correctly, tight, and not worn or glazed. The old compressor could have worn out the belt tensioner. My '02 A/C has a separate belt and tensioner and that is a common issue. A slipping belt will cause cycles of pressure drop and LP tripping. Check the LP switch plug and ware harness. The LP switch will have clear groves on the spades if the connectors are tight. Jumper the plug and move the harness around and see if the clutch cycles. You may have a break in a wire that gets a better connection when you have it off the switch. The freon may still be low. A weak o-ring or seal could leak down to a certain pressure until it's able to hold - like when tires will have slow leaks that stop at 25 PSI but won't hold 35 PSI.

By far the simplest is to take it back to the person that charged the system, since you already paid and it's not working, and have him put on a regular set of gauges (not his charge machine since that's in question at this point) and see if the pressure is really dropping low enough to trip the LP switch or is it an electrical problem. He should do it for free to satisfy curiosity and defend his work. Make you he lets you watch to confirm what he says.

Brakes - You say they have been fine until now with the same components. Air in the lines or bad master cylinder would give you a softer pedal. Stuck ABS parts or a weak booster would make a hard pedal so make sure the vacuum line to the booster didn't get kinked or damaged when all his A/C work was done. Have someone apply the breaks with the truck running while you listen around the booster. If you hear a lot of air whooshing then the booster is the likely culprit.

Battery - I am not familiar with Optima. Is that an AGM battery? I can't see any car battery having a high self-discharge rate or any need for a tender. I would do a parasitic load test to find why the battery is dying. You can do it with any test meter that has a 10 AMP setting. In most cases the cause is a piece of audio equipment not shutting off or a door switch.

Anything can be fixed if the right people work on it.

Keep plugging away.

Hello Grebbler,
Again, you're right, and that's my fault for not quickly writing some numbers down while the machine was hooked to the AC, and watch, and make note of what was occuring. I believe that I did note that the LP Switch was kicking out the Clutch at 25psi.

The weather here the last couple days has started climbing to the 90's already.
I'm going to see how the AC operates this afternoon, and then I can further comment if I've noted any changes of how long the AC Clutch remains engaged?
Mark

 

[MarkD51]

To test the parasitic draw, pull the positive lead off the battery and install a testlight between the battery+ and the cable, the light will light, you can unhook devices and/ or pull fuses untill the light dims, probably wont go out totally, but when you find a circuit with a high draw it will dim down alot on ya.

Another way to keep batteries topped off with alarm is a solar panel in the dash, they make a nice 1'x 4" solar panel with a cig lighter cord that you can plug in and keep the battery fresh, that is what I do when I put a vehicle out of service for a while.

I agree on the weak booster or you could have some collapsed lines also...

I dont like the Optimas.... seen too many have to go back.... could be bad.

Having owned the Tahoe since new, this vehicle has always seemed to eat batteries. Could very simply be the radio? I have checked numerous times, that no lights such as Glove Box Lights, etc are remaining on.

I believe the Fuses for the Viper 5701 Alarm/Remote Start are buried under the dash, and would mean dashboard disassembly again to access.

The code of what trips the alarm that came up on my valet light on the windshield was odd, and I've already discussed this some with the Alarm Shop Owner. The code of a repeated two flashes over and over endlessly pointed at some vibration-thud sensor which was the cause of the alarm tripping.

I'm not sure yet, but there may be the possibility that this Sensor is faulty, or that it might either be able to be "de-sensitized", or perhaps even totally eliminated from the main Alarm Brain Box?

This is actually the second Alarm on this vehicle. The first, which was a Clifford Concept 20, with Remote Start, which was installed a month into ownership did the same thing, an incompatibility with the Deltran Battery Tenders. (I've tried 3 Battery Tenders)

It is to be noted that Clifford was taken over by Viper, that there could be some possible inherit incompatibility issues with the Battery Tenders/Viper Alarms by design?

I know many alarms will activate by design when voltages drop, as the computer brain senses this as somebody possibly ice picking, or somehow disabling the battery to then steal the vehicle. I know it was one common method of how to steal some corvettes, and that there were aftermarket companies making steel battery cases to prevent such draining of the battery to deactivate the alarm systems.

Now that the weather is getting warmer here as we go into spring and summer, I will try addressing these three issues I'm currently facing with the truck, as time, and money allows.

The Viper Alarm Dealer has assured me that I have a lifetime warrantee with this Alarm. In the meantime, the Battery Tender does maintain the Optima Yellow Top, but I cannot arm the alarm also, which defeats the purpose of having an alarm when the vehicle is not being used. Mark

 

[lesterl]

As far as you sensor goes, the power regulation in the sensor is probably questionable and when you put a noisy battery charger/maintainer on it the ripple causes the sensor to falsley detect vibration (which will be a small ripple voltage inside that is measured), either turn the sensitivity down on the sensor, or use a straight DC source like the solar panel.

Of course the solar panel wont work if the 'hoe is in the garage. I would then try some capacitors on the power feed to the alarm and the sensor (start with a 1000uf 25v cap on each and test run).....

 

[MarkD51]

As far as you sensor goes, the power regulation in the sensor is probably questionable and when you put a noisy battery charger/maintainer on it the ripple causes the sensor to falsley detect vibration (which will be a small ripple voltage inside that is measured), either turn the sensitivity down on the sensor, or use a straight DC source like the solar panel.

Of course the solar panel wont work if the 'hoe is in the garage. I would then try some capacitors on the power feed to the alarm and the sensor (start with a 1000uf 25v cap on each and test run).....

Hello Lester,
Thank you for these ideas, and tech advice.

What you say may very well be possible about ripple. And as you say, there may be adjustability with that Sensor also? Pretty much all adjustments to the Alarm are accessible through either the Remote Key Fob Control, or the Valet Switch on the Windshield.

The Car Care site, AutoGeek, which I'm a member of, do sell the Battery Tender Solar Chargers. (3 models) I wonder if the smallest unit would then possibly keep up with any parasitic draw from things like the Alarm, and the Radio/Clock-ECM?

I typically have the Hoe covered with a custom fit Covercraft NOAH Cover when not in use, but I see no issues to possibly extending the cord, might be a simple mod, so that the Charger could be routed outside the vehicle, get sunlight, yet be shaded-protected from elements like rain?

The small Unit is not that expensive.

As for whatever Sensor it is, and if it is for sensing vibration, or objects hitting the vehicle, I have had the Alarm go off a number of times last year when the monstrous Cargo Planes here, going to dump fire retardent on forest fires fly overhead.
Mark

 

[samotahoe]

overcharged?

 

[MarkD51]

overcharged?

When the system was re-done this second time, the mechanic first put in 2 lbs of 134a, then I came back the next day, and he "upped" the charge to 2.2 lbs.

Is this what the 1997 Tahoe with no rear AC supposed to take?

Well, here's a little update.

This morning, I replaced two front wheel studs/nuts that were becoming problematic, got that done in about a 1/2 hour, then was doing some detailing, and paint correction. (it's a work in progress getting through this large SUV, but I'm getting there, with PC7424 and Pads, Polishes, Clay Bars, Iron-X, Wolfgang Deep Gloss Paint Sealant)

After I was done with as far as I wanted to go today with that, I took the Tahoe for a cruise. Temps were 88F degrees.

When I first fired up the truck, the cycling was pretty much like before, about 6-7 seconds engaged, and about 6-7 seconds disengaged.

Once I got out from under the Carport, the interior started warming up of course under direct sun, and the AC seemed to be OK. With a new digital thermometer at the center vent, and on Max AC, set to full cool, at one point, I was reading 39.6F degrees at the vent. It then was staying anywhere from about 44.5F to about 46.3F.

After 5 minutes of driving, I pulled the vehicle over, popped the hood, stood there for 3-4 minutes, and the clutch was staying engaged. Every 5-10 minutes of driving I repeated that process, and watching again for 3-5 minutes, I never seen the clutch disengage!

I took a short drive around town, stopped at the alarm shop, owner wasn't there, but I'll see him next week. After a 1/2 hour of chat at the alarm business, when I got back in the truck, it was of course hot like an oven inside. (doesn't take long down here in southern NM)

So, I took the truck out on the highway, speeds of 50-55mph. AC at center vent was at 44.6 to about 47 degrees.

After about a good 1/2 hour, came back and pulled the truck under the carport.
Popped the hood, Compressor, and clutch was still engaged. Both lines at the evaporator-drier-accumulator cold.

No dripping after shutoff, but might not see this in this weather, since the relative humidity is at about 16-17% today.

So, is it safe to say I may be fine right now, and not have any issues?

Perhaps before, it was just not hot enough outside to call for much AC?
Mark

 

[MarkD51]

Here's a couple of better pics of my Hoe for you Hoe Lovers! :waytogo:
Mark

 

[MarkD51]

I'm tired of the old 16", and Michelin LTX 275/70-16" and tri-spokes.

I'm thinking a nice set of 5-spoke 20"x9" chromes, and 275/55-20 Hankook Sports Tires.
I don't want to get too radical with something 24's, and those skinny sidewalls, or any issues with rubbing.

I need to bring this truck into the 21'st century big time. I think my tire-wheel choices above will be good, but no mods needed. I kinda like the Vision Hollywood 5 as a Wheel. Not to expensive, and I can probably get the combo shipped direct from Discount Tires Direct, Mounted, Balanced, and Shipped. Mark

 

[lesterl]

Nice ride man.....

The shock sensors I remember had a sensitivity adjustment directly on the sensor.....

Those wheels dont look too bad......