AC Air Temperature at Coldest

[stock1992q45]

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Just got a new ac installed R12, 1992 Q and I’m concerned it is not blowing cold enough.

What should the air temperature be coming out when the a/c is on it’s coldest setting and the a/c is working hardest?

Thank you.

[qship96]

All depends on outside/inside temp and humidity levels, fan speed, engine and road speed,etc. Follow checking specs in factory service manual and compare your readings to those listed using EXACT methods described.

What components were replaced? Brand new or rebuilt? details will be useful for further discussion/help/ideas

[maxnix]

Set an AC dial thermometer in the vent. Down the road at more than 30 mph it should be 43° F or colder, but above 34° F.
Modified by maxnix at 10:01 AM 4/1/2008

[qship96]

Set an AC diai thermometer in the vent. Down the road at more than 30 mph it should be 43° F or colder, but above 34° F.

At what fan speed, recirculate on or off, starting interior temp at what temp, humidity,car in direct sun or evening??? so many variables to take into consideration that all affect the final vent temperature- why one must follow the conditions set in FSM EXACTLY to know if system is operating as designed

[captainluigi]

Knowing of course that those conditions will make sure all are on a level playing field.

Hood up? In the garage? Gimme a break! What about some real world conditions?

Mine cheks out well within specs but any Crown Vic will out freeze me in a N.Y. minute.

[captainluigi]

Oh yeah, I have 134 refrigerant. BIG DIFFERENCE!

[qship96]

Oh yeah, I have 134 refrigerant. BIG DIFFERENCE!

Yeah specs list coldest for r134Q at 50 degrees or so= quite different from old Cadillacs,etc which could cause frostbite

[Q45tech]

The FSM has a 126 page section on AC and wonderful graphs and charts showing what the center outlet temp will be at various outside conditions.

The coldest is 46F but I have seen 41-43F after 15-20 minutes at 60 mph.

[maxnix]

Yes, if it is on the colder side, it's not that your AC is super efficient, but that it may be under charged. There has to be a certain mass of refrigerant to transfer the heat from the air via the eveaporator coils to the refrigerant when it changes from a liquid to a gaseous state.

Why evaporator coils freeze and restrict airflow when charge is too low. Seems cold, but not for long.
Modified by maxnix at 10:01 AM 4/1/2008

[Q45tech]

Assuming no leaks and the the evaporator hasn't been replaced in two years the typical problem is dirty filthy slimey evaporator coils.

The proper solution is to remove and clean, but in place foams, solvents, and brushes, and water and compressed air can do a decent job if you have a few hours to spend.

[burijon]

Another thing to consider is to crank the system down to an extra minus 5 degrees. Instead of giving a true temp change it to be + or -.

Check out this old post:

zerothread?id=123035

Obviously you want to make sure of the other things mentioned.

[Q45tech]

We did some studies about 7 years ago and found that the 270 CFM fan was so constipated by evap dirt that 125-145 CFM was all that flowed.

Measuring the installed fan rpm and current draw vs the fan just sitting outside...............shows backpressure. Or just use a manometer to measure the back pressure in front of evap [and thru heater core if you want.

For those scientists here is a 218 page thesis on FOULING of AC evaporators in home and comercial enviroments. The 4.3 year average might be 10 years in a vehicle.http://www.ce.utexas.edu/prof/...n.pdf

When an evap is done it is hard to even bring it back to 66% of new air flow......luckily most don't maintain the system so the acids eat it up and causing replacement.With good mainteance you will get 18+ years of evap life instead of 9-12 so cleaning will rear its ugly head!

[qship96]

Qtech, in a 96Q that has never had any evap. cleaning done since new, and car never smoked in....how much improvement would be gained by injecting a can of the BG foaming cleaner? Can I inject this thru the underhood drain tube, or do I need to remove glovebox and drill a hole in evap. case?

[maxnix]

......luckily most don't maintain the system so the acids eat it up and causing replacement.

Had a friend whe was a refrigeration tech, told me this story when he worked residential HVAC where owners had dogs who liked to mark the AC condenser coils. Took about 2 years for the uric acid to eat throught the aluminum coils.

Qtech, in a 96Q that has never had any evap. cleaning done since new, and car never smoked in....how much improvement would be gained by injecting a can of the BG foaming cleaner? Can I inject this thru the underhood drain tube, or do I need to remove glovebox and drill a hole in evap. case?

My understanding is you spray it in the top air inlet and let is drain out. Wes has a nice post on cleaning his manually.