2 GM dual A/C system jobs; 2 disappointing performances

vcsmike on Mon June 04, 2012 7:50 AM

Year: 2001
Make: Chevy
Model: Tahoe
Engine Size: 5.3
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: 42
Pressure High: 205
Country of Origin: United States

I just replaced the compressor, accumulator, o-tube, & rear TXV, & these are the gauge readings that I ended up with after I charged the system. It was late at night; so although the ambient temp was only 80, humidity was 83%. It felt rather hot. I used exactly 11 oz of PAG 46 & 48 oz of refrigerant. All parts are Delphi except for the rear TXV, which is aftermarket. I pulled a 30 min vacuum, & I let it sit under vacuum for 30 min. It pulled down to 30 in Hg. I flushed the system very thoroughly. I went through over 2 gallons of flush, & I ran a lot of air through each heat exchanger after flushing in order to remove all solvent.

Despite all this, I ended up with a rather disappointing vent temp of 53F, & the rear A/C had a vent temp of 58F. These readings were with both fans on high & with the system in recirculating mode. Driving the car around, the vent temp came down to about 48. Driving the car the next day with the ambient in the low 90's, vent temps were higher than I thought they should be, & there was a very large difference between vent temps at idle & vent temps while under way. Sitting at idle, vent temps were 68, driving at surface street pace, they came down to 58, & at a freeway pace, they came down to 49. These temps were all with the fan speed on its middle setting, the system in recirculating mode, & full cold temp setting. The rear A/C was also on, & its setting were the same.

I did a complete system replacement on a 95 Suburban that I used to own a few years back. The end results were similarly disappointing, & on that car, I also replaced the condenser. In both cases, although I never measured vent temps pre-repair, I could tell subjectively that both performed better prior to their failures than they did post-repair. In fact, the results on the Suburban were even worse than this Tahoe, but I don't remember the numbers. Clearly, I'm doing something wrong, but I can't figure out what it could be.

On the Tahoe, I don't think I have a blend door problem. I ran the blower with the compressor turned off, & the vent temps were equal to ambient. Also, recirculating mode is working properly.

Any input and/or diagnostic techniques to help me nail this down would be greatly appreciated.

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Michael Keith
Vintage Car Solutions
Houston, TX

vcsmike on Mon June 04, 2012 10:35 AM

BTW, I forgot to mention that the fan clutch is about a year old, & it is in good working order. I can hear it loud & clear when I drive away after idling the car for a while.

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Michael Keith
Vintage Car Solutions
Houston, TX

Dougflas on Mon June 04, 2012 10:48 AM

Did you try to clamp off the heater hoses?

vcsmike on Mon June 04, 2012 6:27 PM

I didn't clamp off the heater hoses, but I could. I thought that running the blower with the compressor switched off proved out that issue since I got an air temp equal to ambient when I did that with the motor at hot idle. I figured that if I had an issue with air getting to the heater core, I'd have gotten slightly heated air from the vents when I did that.

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Michael Keith
Vintage Car Solutions
Houston, TX

buickwagon on Tue June 05, 2012 12:50 AM

Quote
Originally posted by: vcsmike
humidity was 83%.

Humid air contains a lot more heat energy per degree of temperature than dry air, therefore the system will not lower the temperature of the air as many degrees when it has to remove a lot of humidity too. Maybe your system is working properly in arduous conditions? You don't mention the humidity the next day, but the system was lowering the vent temperature >40ÃÂ°F when given a decent chance (higher compressor rpm + airflow).

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I've saved hundreds on service by spending thousands on tools.

GM Tech on Tue June 05, 2012 6:03 AM

It IS a Tahoe..they aren't known for the best cooling systems.....

The important thing is- are you happy inside? While driving do you have the urge to open the windows to be able to breathe? Does your wife complain about it? Put the thermometer away and make your decisions. You will pull the rest of your hair out otherwise.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

vcsmike on Tue June 05, 2012 7:47 AM

Quote
Originally posted by: GM Tech
You will pull the rest of your hair out otherwise.

If you saw me in person, you'd laugh at that notion. I have a buzz cut, & I'm danm near bald.

You do raise a good point. It's my wife's car, & she's happy with it. However, in addition to the fact that it worked better before, I'm bothered for three reasons. First is that I do this professionally, & as such, I can't stand a sub-standard result, although I work on vintage Italian cars. Therefore, I don't do a lot of A/C work, & not much is expected from A/C systems in old Italian cars. Second, I'm concerned that there is such a huge disparity in vent temps between idle & freeway driving. I know there should be some difference, but 20 degrees is a bit much. Third, we are not yet at the peak of summer heat here in Houston. I'm concerned that when it gets really hot, the system's performance will no longer be acceptable to she who must be obeyed.

Even more concerning than all that is the notion that, if there is a problem that is allowed to remain, the new system may have a very short life.

As to humidity, I did not note the humidity the next day, but I'm sure it was lower. Humidity is typically much higher at night. I only mentioned the humidity at the time I was charing the system because the ambient temp by itself would be a deceiving number otherwise.

The one component I'm suspicious of is the rear TXV. I was only able to source an aftermarket unit, & it was from the same supplier I used on the Suburban I used to own. Is it possible that I'm getting marginal rear TXV's, & if so, could I isolate that by simply running the system with the rear A/C off?

My second area of concern is flushing. The last time I shot air through the heat exchangers before I put the system back together, I could still smell solvent, although I could not see any solvent vapors. Is it possible that I did not get all the solvent out of the system?

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Michael Keith
Vintage Car Solutions
Houston, TX

GM Tech on Tue June 05, 2012 10:37 AM

Highly possible- that's why I don't flush with solvents-- I use refrigerant...

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

HECAT on Tue June 05, 2012 10:56 AM

What kind of flush did you use? How long did you "Blow" for drying? How long did you vacuum the system?

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FLUSHING TECHNICAL PAPER vs2.pdfÃÂ

vcsmike on Tue June 05, 2012 11:38 AM

Johnsen's A/C flush with a Mastercool flush gun. I blew air through each heat exchanger multiple times in both directions; probably a total of about 3 to 5 minutes of air per exchanger. No visible flush vapor once I was done, but the return air still smelled slightly of flush solvent. I liked the flush gun on your web site. Do you sell direct, or only through your distributors?

GM Tech- Refrigerant flushing sounds interesting. Any way I could find someone in the Houston area that does that?

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Michael Keith
Vintage Car Solutions
Houston, TX

GM Tech on Tue June 05, 2012 12:08 PM

All GM Dealerships are required to use their recovery machines to flush with-- they have all been supplied with flushing kits-- whether they use them is up to them.

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

buickwagon on Tue June 05, 2012 3:21 PM

Quote
Originally posted by: vcsmike
As to humidity, I did not note the humidity the next day, but I'm sure it was lower. Humidity is typically much higher at night. I only mentioned the humidity at the time I was charing the system because the ambient temp by itself would be a deceiving number otherwise.

Relative Humidity is, well, relative. It's a measure of how much water the air can hold at it's current temperature, not an absolute measurement of how much moisture is in the air. RH rises at night as the air cools not because there is more moisture at night, but because cooler air can't hold as much moisture as warm air can. In other words, four ounces of water is four ounces of water: there's still just as much water no matter if it fills a 5 oz dixie cup 80% or an 8oz coffee mug 50%. From an AC standpoint, the latter might be even worse, since it's warmer water in the coffee mug.

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I've saved hundreds on service by spending thousands on tools.

TRB on Tue June 05, 2012 4:44 PM

Refrigerant Flushing machines work very well.

Hecat H1000

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Edited: Tue June 05, 2012 at 4:44 PM by TRB

HECAT on Wed June 06, 2012 3:29 PM

Johnsens makes more than one flush and I could comment more about the chemistry if I had the specific one you used. Regardless we have found that a minimum of 20-30 minute blow time is needed to remove the solvents that will evaporate, and the ones that don't should never be put in their in the first place. Based upon your blow time I do agree this may be a big contributing factor to your system operating problems. I would also be concerned about the condition of your vacuum pump oil (solvent contaminated) and its ability to pull good vacuum.

Solvent flushing can and is done correctly every day. But unfortunately, when done incorrectly it causes more problems than it resolves.

Any and all HECAT flushing products are available from this site's sponsor.

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