Automotive Air Conditioning Information Forum (Archives)

jtupper on Tue September 01, 2009 1:55 PM

Year: 2000
Make: 2000
Model: Tahoe
Engine Size: 5.3
Refrigerant Type: R-134A
Ambient Temp: 88°
Pressure Low: 54
Pressure High: 275

I finally got my hands on a set of gauges and these are the numbers I came up with. It's about 88° with 65% humidity. Numbers taken with max a/c on recirculate and windows down.

At idle: Low - 50 High - 220 center vent temp - 60°

AT 1500 RPM: Low - 54 High - 275 center vent temp - 56°


When I turn the fan speed to it's lowest setting the comporessor does cycle. Is my sytem overcharged?

TRB on Tue September 01, 2009 2:03 PM

Numbers look fine compared to the chart. How much refrigerant was added to the system?

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jtupper on Tue September 01, 2009 2:34 PM

That's the thing. He said he added a total of 6 cans, which would be 72oz. I asked why he added so much and that it only called for 48oz. and he said he lost some of it out of high pressure service port. It is leaking slowly when you remove the cap. I don't see how he could have lost 24oz. worth of refrigerant with that leak.

Judging by the chart you supplied me with my order, I was expecting the low side somewhere in the low to mid 40's, not low to mid 50's. I have gotten a vent temp of 40° at highway speed on a low fan setting though.

HVargas on Tue September 01, 2009 2:38 PM

Sounds like an overcharge and at highway speed you are just getting enough airflow to compensate. The best recommendation we can have is to take it somewhere that can physically tell how much they evacuate and have the proper amount put in by weight instead of a round about guess.

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jtupper on Tue September 01, 2009 2:48 PM

Is this something I could do myself now that I have access to a set of gauges and a vacuum pump?

TRB on Tue September 01, 2009 2:53 PM

72 ounces is way too much refrigerant! I would take it back and have them reclaim the refrigerant and then properly evacuate and charge you system.

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jtupper on Tue September 01, 2009 3:01 PM

I guess you get what you pay for sometimes. I'm about $700 into this repair and was looking to save a few bucks

I took it to a reputable a/c shop to have it flushed, but I have a buddy who works at a repair shop that vacuumed it down and recharged it for about half of what the a/c shop wanted. I'm not sure he has the ablity to reclaim the refrigerant (I'm assuming you mean to re-use the refrigerant that's in there now).

jtupper on Tue September 01, 2009 3:09 PM

One more question...what kind of pressure readings should I be looking for?

HVargas on Tue September 01, 2009 4:30 PM

Your low side numbers are a little high. I would try to get them around 28-35. High side numbers weren't too bad. Should be 2.2-2.5x ambient temperature. So figure in the range of 195-220.

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Chick on Tue September 01, 2009 4:35 PM

Have it charged into a deep vacuum the correct amount, then check the pressures and cooling, guessing at the amount is a recipe for trouble..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

jtupper on Wed September 02, 2009 1:24 PM

As suspected, the system was overcharged. The shop reclaimed the refrigerant, replaced the high side service port valve that was leaking and recharged the system. They pulled out 3.2 lbs.; the system only calls for 2.75.

As far as I can tell, it is cooling a little better. The real test will be on the next really hot day. Temps at the time of the recharge were only about 80°. I looked at the gauges and the low side read about 40 and the high side was about 185-190.

Are there any effect of the overccharge I should be concerned with? I ran the a/c very little over the last 4 days because I was fairly sure it was overcharged.

Edited: Wed September 02, 2009 at 1:24 PM by jtupper

jtupper on Wed September 02, 2009 6:47 PM

Now I am as confused as ever. When I got home, I hooked up my gauges to get pressure readings at 1500 RPM (the reading at the shop was at idle). At 1500 RPM my low side went down to about 45 but the high side went up to about 290. It's 96° outside so it should be somewhere down arounf 240 for the high reading.

Any ideas???

HVargas on Wed September 02, 2009 6:57 PM

With an ambient of 100* and 40% humidity Mitchell shows that 290psi is an acceptable reading. Ignore my previous post. I was thinking you were converting for some reason.

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jtupper on Thu September 03, 2009 1:31 PM

Tim sent me a copy of that with my order. It's at home but if I remember correctly, 290 is the maximum at 90° and 70% humidity (it was about 96° and 65% humidity at the time).

It looks like I'm at the very upper end of where I should be. Should I be concerned at all? Is there anything I can do to bring that down?

Chick on Thu September 03, 2009 1:59 PM

Just make sure you're fan(s) are operating properly, the pressures will drop when you're moving.. if you have an electric fan, it should be running around that pressure, the fan clutch if equipped may be nearing the end of it's life..But still, those aren't bad pressures for near 100 degrees....

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

jtupper on Thu September 03, 2009 4:51 PM

AFAIK, the fan is working properly. It's definitely cooling better. I'm getting vent temps consistently in the 40's with just normal city driving where before I had to get up on the highway to do that.

I'm a little disappointed that the rear system doesn't blow colder than it does, but it never blew all that cold to begin with. I really figured that it would improve when I did all of this. Maybe that's just normal for this vehicle.

jtupper on Mon June 13, 2011 10:25 PM

I hate to dig up an old thread here, but I'm having some cooling issues still. Obviously it's been as hot as Haites here in Texas lately, but my AC is just not working quite right. I will have to get some gauges to get the latest readings but when I'm not moving at idle, it just blows cool...not cold. I have also noticed that the compressor is not cycling. When I'm moving, it cools great.

The other day idled it up to about 1200 RPM and it started blowing colder, even sitting still. As soon as I let it go back down to idle, it got warm again. Obviously, readings are necessary, but the comp. not cycling worries me,

TRB on Mon June 13, 2011 11:28 PM

Check for leaks.

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jtupper on Tue June 14, 2011 9:59 AM

I noticed this morning that the lines after the OT are frosting up where they normally would just condensate and sweat. Is that indicative of low refrigerant?

What's the best method for checking for leaks? I used ester glow when I replaced everything so I assume I just need to pick up a UV light?