Yet another A/C question

[JohnC]

Ever since I got my '95 (in '96) I've felt the A/c was marginal at best. It has 2 issues that I'd think were mutually exclusive. First is it tends to freeze up on hot, humid days on the highway. I know it freezes up because the airflow pretty much stops until you shut the compressor off and let it thaw out. Second, under all other circumstances, the air temp in the ducts is luke warm (what does that mean?) Anyhow, yesterday, OAT 92, duct temp 55. There has been no change in the 9 years I've had it, it's never been serviced, and it is a 134a system.

Any ideas?

[HowieE]

Both of your symptoms are indicative of a low charge but not a low enough charge to open the low pressure switch. The first is have someone put a set of guages on the system, preferably on a hot humid day while the thermostat is set for heat and the doors on the truck open and a fan across the radiator. This setup will simulate about the highest load possible on the A/C system and give a good indication of the charge.

If the truck has a low charge and has had that level of charge for several years at least you don't have a leaker because any leak would have cause the charge to drop below the low pressure cut off point in that time.

[JohnC]

I figured low charge would cause it to freeze up, but I figured the high duct temps would have a different cause. If it's just low, could I just shoot a can of 134 into it and cross my fingers? Not to many competent folks out here in the boonies...

[DChristie]

Good morning!
I also have the '95, it had the anemic A/C. I found it was full of dirt and leaves, choking off the air flow.

Last week my A/C was on the fritz also. So I charged it, only to discover a leak in the aluminum tubing at the rear of the compressor. I welded that up, added another charge and same symptoms as you describe. Low flow and warmish air temp. One of my friends here asked if I had ever cleaned or changed the filter. "What filter I asked."
No luck as I tried to find it, either in the truck or in the books. I have no idea what he's talking about, still haven't cleaned or changed it.
My solution; I removed the squirrel cage blower-motor and cleaned copious handfuls of pine needles and leaves and dirt out of the coil inside the box. I had a devil of a time getting access to the inside.
I used my shop-vac and a coarse spray from the garden hose (I lined the carpet with plastic to guide the runoff out the door.)After the "cleaning" it blows more and colder air than ever before, I suspect it could improve a little more still. But I think I would have to remove the entire dash to get to it.
Anyway it's much better now.

Hope this helps.

DChristie

[HowieE]

If you have good air flow from the ducts with just the fan on you can assume that dirt in the fan housing is not your problem. If your compressor runs when you first turn the A/C on I would go ahead and put a can in. Again try to do the charging at the hottest possible time of day with the doors open. Watch the suction line coming back to the compressor. You can charge until you see condinsation on the suction line all the way back to the compressor. That should do it.
Take a look at my web site for what you might finf forward in the condensor that effects things.
http://mysite.verizon.net/vze54tx9/

[JohnC]

Originally posted by HowieE:
Take a look at my web site for what you might finf forward in the condensor that effects things.Yeah, mine was the same way. Probably time to clean it out again. IIRC, both oil coolers have "diagonal" airflow paths, so the "detritus" has to make at least a 45* heading change when it hits the condensor. Fat chance...

[charliepeterson]

John if you have a problem with the orifice screen you could be starving the evaporator. On the '95's it's in the line coming out of the condensor at the condensor.

With the truck running look at the lines from where the icing is starting. You really should start with a weighed charge though. Unfortunately more is NOT better with 134A.

Another way is to add one can and watch what happens. Try to be patient if you open up the line at the condensor. You will have to dump the charge and use some heat. This can get very expensive sometimes because the fittings tend to weld themselves together.

Just keep in mind that the life expectancy of this system is only five years. After this it doesn't owe you anything.

[DA BIG ONE]

Once you have a handle on the issue use a VOV (variable orfice valve)in place of the fixed orifice expansion valve. It will make the ac colder at idle and in slow traffic. http://www.aircondition.com/vov/

Another mod for ac is using a plate style condensor in place of the common tube and fin type. http://www.vintageair.com/

[JohnC]

Originally posted by charliepeterson:
...Just keep in mind that the life expectancy of this system is only five years. After this it doesn't owe you anything... Yeah, I know. But the clock doesn't start 'till it starts working correctly, right? ;)

[charliepeterson]

Yes, I guess you could say it starts when it runs correctly. :>)