70Deville A/C Coolness Fades?

[Tim]

I have a 70 Deville CVT with Factory Comfort Control. A/C works fine and blows really cold at lowest setting, however after about 30 mins of use, even with the blower on the higest setting the A/C fades and barely blows cold air. Fan works fine, but the air is not very cold coming out of the vents. Could it be as simple as low freon? Or is this a symptom of more serious problems. Other concern is the new type of freon. I have some of the old stuff left, but if I need to switch to the newer type, what components if any need to be converted? Yes I know, I can drop the top and not have the A/C on, but I want both. Thanks for any responses. Tim

[Bruce Reynolds # 18992]

Gday Tim,

Firstly, it sounds like the Freon is low.

Secondly, I will leave the rest of the answer to experts in this field.

But, there is an equivalent to R12 instead of going all the way to R134A replacement.

Bruce,
The Tassie Devil(le),
60 CDV

[Porter 21919]

Tim,

Auto AC is a specialized field, you cant expect anyone here to diagnose your problem, there is no simple answer to your problem that I know of. I believe if you are low on freon you would never be "cool".

Find a reputable AC specialist and have them diagnose / correct the problem.

Dont get me wrong, there are many experts here in numerous phases of auto repair, AC specialists have the proper equipment and do it day in and day out for a living.

Porter

[Jerry CLC #13469]

Greetings,

I just had the A/C on my 70 CDV serviced with 4 1/2 lbs of freon
an am experiencing the same problem.

Someone at the 2005 GN suggested the problem might be the evaporator or related A/C component.

This question might be better addressed at the technical site.

[Andrew 10642]

First of all, all the above advice is correct!  you should get someone who is an a/c person look at this.  however, time for a wild a$$ guess.

Your evaporator may be iceing up, perhaps due to excessive dirt, which might explain why it works perfectly for a half hour.

Less likely is a mode door that is screwed up.  Dont know why it would work for the first half hour.  Could also be an intermittant electrical problem, so you would be back to the A/C problem.

Go to your local library and get a Mitchell repair manual for that model year, or buy the Service Manual, which is the better resource.

Remember to let us all know what the problem was!

[bill henry]

the shop manual says you will have this exact problem if your suction throttling valve is set slightly below 28 lbs causing evaporator icing and loss of airflow

[Denise 20352]

  I would wait until the air wasnt blowing cold, then open up the hood and feel the hoses around the evaporator.  If theyre nice and cold, then there might be a problem with the system not opening the right ducts.  Then I would put it on "defrost" and see if it blows cold up there.  That would isolate the problem to one end of the firewall or the other.

  If the evaporator is icing up, I would expect that the airflow from the vents would be reduced, all other things being equal.

  Some people recommend "Freeze 12" as a substitute for freon, but I dont know anything about it.

-denise

[Tim]

Thanks for all of the input, I have an appointment on Thurs to better determine what is going on ( or not ). Thanks for the responses.
Tim

[Mike #19861]

 First of all, like Porter said, taking the car to an experienced AC technician is the best move. Someone who knows these systems and wont steer you wrong.

 But, there are a couple of things that could be going on that you can check yourself. I would suspect the throttle suctioning valve first. Sometimes they become restricted preventing proper flow. You will see this by an ice buildup part way back on the valve.

 Check the belt tension. Slipping belts will not allow the compressor to operate correctly. Oil on the belts can allow them to slip without squealing also.

 Normally, when an evaporator ices up, it restricts the airflow through the ducts. If you turn the system off for about 15 minutes, then turn it on again, and airflow and coolness return, then that may be the problem.

 A system overcharge can cause both these problems. Have the tech put on a set of gauges and watch the pressures. Typically, the high side pressure should be double the ambient temperature.

  Mike

[Tim]

Update: Took Deville into repair shop and brought my trusty container of R12 with me. The freon was low and they brought up to the max level. I will try it over the labor day weekend and see how it goes. Thanks for all of the tips.
Tim