97 Lumina normal A/C duct temps 3.1 Engine

[jimbob0077]

Can someone tell me what I should expect for normal A/C temperature output to the left center duct with the blower at max speed and A/c set for recirculation. Outside air temp 85 degrees about 50% humidity, car sitting at idle for twenty minutes. I had it in drive with the brake on. That is after taking a 35 minute drive. Everything should be heat or cold soaked by then. Don't want to say what reading I got until I get feed back.

[jeffcoslacker]

I don't know what "spec" is for these, but typical is if you're putting out 40-45f you're in good shape.

I've gotten them to run below freezing before, which feels wonderful but the evap core turns into a block of ice real fast in humid conditions

[DeltaP]

Probably around 60'.

[jeffcoslacker]

Originally Posted by DeltaP

Probably around 60'.

If you were only 25 degrees less than ambient you'd never cool a car down...especially in sun.

[DeltaP]

That looks like a GM chart but is it specific for that exact car? The dealer will tell ya 20 degrees less than ambient is acceptable. Mind you he said it was sitting idling in drive for 20 minutes. I'd like to see what he has to say.

[jimbob0077]

60 degree's is what I'm getting. Fun thing is if I run for at least 35 minutes at 55 to 60 mph the duct temp at the lowest fan speed setting #1, will be 35 degrees. Two years ago, on the way back from Florida, my compressor or clutch started to squeal. The repair place, replaced the compressor+clutch, orface tube and accumulator. It was cold and raining. About an hour after leaving on the inter state the evaporator froze. Runs great around town. The mechanic in apple valley said the evaporator was going down to 28 degrees. He said he put a 1/2 can of refrigerant in the system and declared it good. On a four hour trip the evaporator froze. Put my manifold on the system. Low side 32 High side 225. Average due to radiator fan, intermittantly going to high speed. I took the fan and resistor pack out of the phenum and cleaned a small amount material on the face of the evaporator. Now, Lowest temp at 55 mph and recirc with fan speed #1 is 36 degrees. Wife doesn't like the newest higher temp but I'm concerned about trying to run a lower temp as evaporator will freeze. So are you pretty sure that this is the best this car can due? Thanks for your help.

[DeltaP]

It's hard to diagnose your car from here. I'd be happy with what you're getting on a car of that year. Clean your condenser. Hose it out with a garden hose. Be carefull trying to clean the evaporator by hand. You can do more damage than good. An evaporator coil cleaner might do some good sprayed on and rinsed immediately followed by some deodorizer. Coil cleaner has an acrid stink to it. She certainly wont like that. Debris on the coil will promote freezing. Good luck.

[Tech II]

Rule of thumb is, run the vehicle at at full cold position with A/C off(car going down the road)....read temp.....now turn the A/C on......read temp.....temp should drop a minimum of 30 degrees....

I think we have a capacity problem here......really unknown how much refrigerent is in the system, since we have guys adding 1/2 cans...only accurate way to add freon is recover and evac the system, then add freon by weight......

[Schurkey]

Originally Posted by Tech II

Rule of thumb is, run the vehicle at at full cold position with A/C off(car going down the road)....read temp.....now turn the A/C on......read temp.....temp should drop a minimum of 30 degrees...

I've come to trust your opinions on most everything; so hearing that from you makes me question my sanity. I quit working on A/C professionally two decades ago. A/C systems must have really taken a performance dump since then...or I just happen to live in a place where I never had to deal with crazy high ambient temperatures.

Thousands of years ago, dinosaurs ruled the earth. A/C systems were controlled with a POA/STV; and they could be adjusted to provide 33 degree evaporator temperature--just above where the evaporator freezes.

In an effort to cut costs--(deceiving the public by pretending to make the system more "fuel efficient")--GM went to a cycling compressor clutch system. The moderately-expensive, precision-made POA/STV was replaced with a thirty-cent plastic screen that had a metal orifice molded into it, and an O-ring to seal it inside the refrigeration pipe. The duct temperatures were now in the 40--45 degree range, instead of 35 degrees. The only fuel economy gains were from a mechanically more efficient compressor, and the REDUCED COOLING provided by the new system.

If an A/C system can't provide 45 degree duct temperature, there's something wrong. 60 degrees is crazy. I absolutely guarantee you that if I had 90+ degree duct temps because it was hotternhell outside, and the A/C system I just worked on only reduced the temp by 30 degrees...customers would have had my ass on a flagpole.

Ambient temps vary, duct temp was fairly stable. The high-side pressure went up as ambient temp increased; and you can kiss "goodbye" to any clutch cycling--that "fuel efficient cycling clutch" compressor ran constantly just like with the old STV systems.

I'm trying to understand how we can be so far apart on this. There must be something I'm not understanding.

Originally Posted by Tech II

I think we have a capacity problem here......really unknown how much refrigerent is in the system, since we have guys adding 1/2 cans...only accurate way to add freon is recover and evac the system, then add freon by weight......

I understand that young guys would believe this. It's what you've been trained to do; and it gets the charge very close without wasting refrigerant OR a lot of time thinking. Also eliminates arguing with the customer because the shop can point to the "factory specs"; as long as they added the "correct" amount, they figure they're off-the-hook for performance issues. So, sure, it's a successful and politically-correct way to service the unit. (Most of the time.)

'Course, it assumes that you've got access to the multi-thousand dollar recovery unit/recharge station.

It also assumes that there's no aftermarket refrigeration-system changes, such as a replacement hose that has a muffler that the OEM hose didn't; or an extra-large condenser in place of a regular-size condenser because the correct size condenser is discontinued. Recharging based on adding a specified weight of refrigerant is inaccurate as soon as the capacity of the system changes from OEM spec. Truth is, adding by specified weight is a great way to be close, but not exact in the best of circumstances.

In the old days, the mechanic would top off refrigerant slowly until the MAXIMUM COOLING was achieved--add some, watch the thermometer in the duct. Add some more, check the thermometer. When the thermometer JUST starts to go UP--maybe a degree or two--you've there. That procedure works on ANY vehicle, even if the cooling system doesn't meet OEM specs for capacity.

[jeffcoslacker]

I've forgotten most of what I used to know about A/C...so take my thoughts with a grain of salt....

I remember some systems would ice the evap core when they were LOW on refrig, topping them up corrected it. I can't remember WHY, exactly, but I remember it happening. Your pressure readings seem a bit low for an R-134a system, at least to my memory, if this was a hot day when you got those readings. R-134a systems tend to run a bit higher than Freon pressures did. I'm thinking you got room to charge a little more and see what it does. And MIGHT correct the icing, but I can't swear to it. If it makes it worse, you can always blow some off....

I always charged by feel or thermometer, not capacity. I've only blown a couple up ...and they had issues anyway. I usually run a hose to let water flow over the condenser while charging too. Makes it inhale more willingly and gives you a more predictable "baseline" for what you feel from the vents, instead of trying to factor in ambient temps and all...cooling it with water makes the ambient temp kind of a non-factor. Once you get used to what one should feel like when charged like this, you can repeat it regardless of ambient temp, in other words.

Long as the pressures don't skyrocket above spec when you stop the water, you're good.

When i said I was able to force 28 degree air from the vent but at the cost of icing up the evap, that was on a '77 Ford LTD that I retrofitted for 134a. My first one, actually.

[jeffcoslacker]

Originally Posted by Schurkey

In the old days, the mechanic would top off refrigerant slowly until the MAXIMUM COOLING was achieved--add some, watch the thermometer in the duct. Add some more, check the thermometer. When the thermometer JUST starts to go UP--maybe a degree or two--you've there. That procedure works on ANY vehicle, even if the cooling system doesn't meet OEM specs for capacity.

I miss sight glasses...sigh....best way to charge IMO. When it showed clear, you're there. No guesswork....

It's a dirty trick, but on a few cars I've owned, I've installed a dash switch that directly powers the compressor clutch and overrides the pressure limit systems...solved a lot of my lack of cooling on the highway or extended idling problems or whatever....always figured I'd blow something up, but never did....

Going WAY back...I had a '71 Dodge Polara I retrofitted...and put a huge electric fan off a minivan in front of the condenser in a pusher arrangement...of course there was plenty of room to do this on an old boat like that...and I simply ran zip ties through the condenser core fins, put little square pads of radiator hose rubber under the "feet" of the fan's cage...

We were messing with it at my uncle's auto A/C shop after I got done...evac'd it and laid a full charge on it...vent temps would drop 8-10 degrees with the pusher fan on as opposed to off...I'd say it worked well

[Tech II]

Quote:Rule of thumb is, run the vehicle at at full cold position with A/C off(car going down the road)....read temp.....now turn the A/C on......read temp.....temp should drop a minimum of 30 degrees....
Originally Posted by Tech II
Rule of thumb is, run the vehicle at at full cold position with A/C off(car going down the road)....read temp.....now turn the A/C on......read temp.....temp should drop a minimum of 30 degrees...

I've come to trust your opinions on most everything; so hearing that from you makes me question my sanity.




Rule of thumb to me, is a general rule, not something cast in stone.....notice the word minimum?

If you have worked flat rate lately, our times just seem to get squeezed more and more......so you have to work within guidelines......you evacuate and recharge by weight and get the job done.....I could spend more time fine tuning the system, but I am not going to get paid for it....and more often than not, charging by weight is better than someone adding cans and not knowing how much they put in.....putting in too little and putting in too much is just as bad.....I find by weight a happy medium....

As far as I'm concerned, I agree the old R-12 systems cooled better than the R-134a systems.......but you work with what you have to work with....

Hope I didn't force you into a padded cell.....

[jimbob0077]

Thanks for the responses. Went to a chevy dealer and two guys there said I shouldn't be satisfied with 60 degree air (center duct ) at idle. Connected a manifold to system, engine rpm 1500. Air temp 90. Low side 55 High side 225. So I tried draining (venting) some of the refrigerant to get the low side to come down. No help. So I then added a half can. Low side 50 high 225. Gave up and drained system. Connected vacuum venturi powered by my air compressor to system and it went down to 27 inchs hg. got worse (losing vacuum) as my compressor got hotter 25 inchs hg. Decided I'm going to buy a vacuum pump. One question. Bought a black light and noted small amount of leakage around back of clutch. Isn't that normal for a Chevy V5 compressor? Dont' want to change a $460 pump that a shop installed two years ago in Indiana, when A/C started squealing returning from Florida. Total bill approx $900. I'm not happy.

[jeffcoslacker]

V5's do like to leak from there. That's where my problem currently is too. But I'm slinging enough oil there's no doubt...whole compressor face gets wet with a charge and running. But it also blows a whole charge in a few days.

You can get a comp for it at O'Reilly's for around $260 for the good one, cheaper for the others they carry...that sounds like shop parts upcharge, what you quoted...

Me, I'm gonna go try to find a good boneyard unit off a last gen Monte Carlo with the 3.4, $39-$45 around here (same compressor) and see what happens....