A/C question inside (diesel related)

[mdregister]

What does the rubber insulative housing around the blower motor and evap core do exactly?? Does it insulate against noise or heat (or both)?

Does the A/C function better with it?

When the A/C is on the MAX setting, where is the physical point where the inside cabin air is "recycled" back into the vents? I know on most cars it is on the passenger side floor area under the dash, but I can not find it on my 85 suburban.

The reason I ask, is that I am frickin dying in the heat and I am looking for ways to improve the effectiveness of the A/C. I do not have rear air on my 85 suburban, so I am trying to squeeze as much performance I can out of what I have.

Here is what I have done so far:

A/C was low on freon, so I had it charged/converted to the new stuff :(

cleaned evaporator with brake cleaner

Wrapped "cold" A/C lines and condenser with insulative pipe wrap

re-sealed leaking joints in all the plumbing under dash I can get to

replaced blower motor/fan assembly.

Things I want to do:

I want to block off areas of the ducts where I get cool air that I do not want. There is a "foot cooler" hole right over the brake pedal that I am going to cover, it always blows cold air on my feet no matter the setting.

I also want to remove the floor duct in the center of the cab that directs heat. This duct also always blows cold air when the A/C is on. I have been afraid to do this as I thought maybe this was also a return point for the A/C on the MAX cycle.

Any suggestions?

[ 08-07-2004, 04:54 PM: Message edited by: mdregister ]

[jbell]

sounds like I have a sububan exactly like yours.
Here's what I've done.
1. removed completely the plastic duct that goes over to the vent by the driver door, and plugged that oval shaped hole with foam. Don't need the foot cooler..... or that other vent either.
2. the return air is on the passenger side kick panel, you'll see a vacuum motor to open/close for fresh/recirculate air. If I wanted fresh air, I'd open the wing windows -- it's on permanent recirculate mode.
3. blocked off the floor vent as it only closes it appears in defrost mode. (no idea why) Actually I removed the deflector piece of plastic, added a solid flat piece of 1/4" plastic to bock off the passage / hook up a pair of 1 1/2" flexible pipes, that run under my custom center console to a pair of openable round vents on the back of that console, that the middle row passengers can use, to keep them cool.

That was enough to get good airflow through the remaining three front vents, and having vents that direct to the mid seat passengers is a real plus without a rear ac.

I am also not using r134a... that stuff will never get cold.

[catmandoo]

you can always put a valve in the inlet hose to the heater core to shut off hot water flow thru the heater core.my old chevelle has no air and black interior and the water valve is a godsend

[Mark Krieger]

I read your post and it's interesting to see the things you've you've tried. A/C is kind of mysterious to most folks and there's good reason. I've learned a few things that might be helpful.

(1) The larger cool-to-the-touch vapor lines happen after the freon has passed through the passenger compartment and it's being recycled back to the compressor. Insulating them won't really help the system work better. The smaller hot-to-the-touch liquid lines (I know it sounds strange) are headed toward the passenger compartment. Keeping these from getting hotter might actually help!

(2) The air blowing out of the dash should be no more than 45 Degrees. A good working system will blow between 35 Degrees and 45 Degrees. It's hard to judge by hand, so a good little thermometer will work best.

(3) If the air out of the vents isn't as cold as it should be, compare the temperature after a few minutes idling to the temperature after a few minutes moving down the highway. If it gets cold on the highway and not standing still, it's an airflow problem through the condenser that you need to address. If it's never cold enough, it's typically a system problem.

(4) Assuming that your system doesn't have any air inside and it's all R-134A or R-12, it'll actually get colder as the freon runs lower. Too much freon will actually deliver warmer air. (Another strange fact.)

Measure the temperature of the air coming out of the vents, I'm willing to bet that you're getting air that's closer to 50 Degrees. Tell me the temperature after idling for a while, and then again after moving down the highway for a while and I might be able to tell you where to look next.

Pinching off the heater hose with a clamp and then repeating your measurements will tell you if that's the source of trouble too.

[mdregister]

ty for the replies everyone.

Mark, I will try the things you suggest and get the data back to you.

I can tell you this already- The A/C is MUCH colder when moving down the highway, almost comfortable in fact smile.gif
.

However, AS SOON as I stop, the air gets lukewarm.

[mdregister]

ty for the replies everyone.

Mark, I will try the things you suggest and get the data back to you.

I can tell you this already- The A/C is MUCH colder when moving down the highway, almost comfortable in fact smile.gif
.

However, AS SOON as I stop, the air gets lukewarm. This is indeed the reason behind my question about the function of the insulation around the condenser. I was wondering if I would be better off removing the insulation all together and POSSIBLY even mounting a 12v fan to increase heat exchange at idle.

[diesel65]

If you have air coming out the floor vent when in the a/c mode (or even in vent mode)you need to check the servo to door anchor.
The anchor is made of plastic and they do break.
To check the anchor point, you first take the glove box out then at the left side of the opening there is a duct that has to come out, it is held in place by three screws, there is a fourth screw that anchors the upper duct that has to come out.
Once you get that duct out you will see the door and the white plastic piece that anchors the servo rod.

[Mark Krieger]

Measure the temperature while you're moving. Even though it FEELS cold, it isn't working right if it doesn't get down to 45 Degrees or less at the vents. The fact that it improves a noticable amount while you're driving is GOOD news because it's relatively inexpensive to fix this part of the system.

If, in fact you get cold air while moving down the road, the problem is on the condenser side of the system. There's nothing better that 45+ MPH air across the grille to make the system work good! The problem is this, improve the airflow at idle...

At idle, you need enough air-flow through the condenser to keep the system operating near full capacity. There's two things that'll keep this from happening.

(1) It's almost a sure-thing that you've got debris between the condenser at the front of the vehicle and the radiator behind. You won't see it unless you remove the fan shroud and look down between the two. Trust me, you'll be amazed the amount of junk that hides there. I didn't believe this advice until I dis-assembled my 1995 Suburban to replace the water pump and I couldn't believe my eyes; it's amazing it worked at all! Unless you've had it apart in the last couple of years, take it apart now and clean it up so it's like new again.

(2) A 1985 truck is likely to have a well-worn fan clutch. This clutch is critical to getting good air flow at idle! After you've cleaned between the radiator and the condenser, and with the engine hot and idling, you should feel ALOT of air movement into the grille. Some say it should be strong enough to hold something heavy like a shop towel or a hat against the condenser. (Imagine a house fan of the same size and you'd expect it to suck up anything nearby that's loose. The truck fan should too.) Before you go and fix the complicated A/C system, make sure the simple fan-clutch is working like it did when it was new.

[jbell]

diesel65 --
you are correct on the floor vent. I thought that was originally the problem as well. But mine closes and works correctly on defrost mode only!! for some other reason on my 85 sub, it's open in all other positions. I haven't checked the controls -- but it acts like gm intended for it to work that way. The "foot cooler" is also open and blows air on the drivers feet regardless of heat or cool -- does that make any sense?

[mdregister]

Allright, the results are in:

This morning I wrapped the "hot" lines in pipe insulation as well. I also cleaned both sides of the condenser and radiator with brake cleaner followed with a jet of water. The area between my radiator/condenser was dirty, but not a whole lot of debris.

With an ambient temp of about 85 degrees farenheit, my results where:

At highway speed my vent temp was 52 degrees with a humidity of 70%

At idle my vent temp is a balmy 75 degrees at 70% humidity.

I am hot <sigh>

[Mark Krieger]

You said you had it changed and/or filled.

What do you know about what they did? Did they do it cheap or did they do it well?

This stuff is only plumbing! If there's nothing blocking air-flow and nothing clogging the pipes then we need to figure out whats inside the pipes.

Here's what they should have done to insure good results. Short-cuts will deliver luke-warm results. (No pun intended)

(1) Evacuate the R-12 from the system.
(2) Flush the system with solvent to remove debris and the R-12 compatable lubricant.
(3) Dry the system and evacuate it by deep vacuum for 15 to 30 Minutes.
(4) Install R-134 compatable lubricant in the proper amount.
(5) Charge the system while observing pressures to verify a proper amount of R-134A.

Some shortcuts that'll deliver bad results...

(1) Mixing R-134A with R-12 and failing to change the lubricant.

(2) Adding lubricant to whatever is there already. Too much oil will mix with the freon and dilute its cooling ability. If the amount of lubricant in the system was unknown, flushing and re-filling will make it clearly known.

(3) Failing to pull a deep vacuum to purge the system of air and moisture or anything that's not freon and oil. Adding R-134 to any air inside the system will deliver luke-warm results.

(3) Over charging the system or failing to achieve the proper operating pressures. Less R-134A (by weight) is required in the system than R12.

How much of this do you know for a fact was done or not done?

The bottom line is this, if there's no blockage and everything is assembled clean with the proper amount of lubricant, the system WILL work. It's so easy to cut corners and there's so little common knowledge of what's right and wrong that it's easy take shortcuts that'll deliver poor results! A system mixed full of oil and air and a soupy mixture of junk can't help but work poorly.

If I had to guess, they didn't pull a vacuum and didn't flush the system. They probably added MORE oil without knowing what's inside and topped it off with R-134 before sending it out the door. With any luck, they at-least checked the pressures to make sure they didn't over charge.

The quality that seperates an A/C EXPERT from an ordinary mechanic is CRAFTSMANSHIP! It's really NOT rocket science.

[mdregister]

I really am not sure of all the particulars of the work done. I had the system converted right after I took ownership of the truck. I guess I will have to do some asking around to find a good local A/C shop.

[diesel65]

jbell,
It has been awhile since I last saw a old OBS suburban with the a/c problem I described, I think the symptom that you described is an indication that the plastic anchor piece is broken.
Why not pull the glove box like I said and check, it should take about 10-15 minutes to pull it apart.

[mdregister]

I purchased a little cheap guage for checking the 134a pressue.

What should my system read on the low pressure side at 90 degrees ambient temperature?

I am reading 62psi which sounds high to me. I think it is supposed to be 45-55 psi.

Can I relieve some of the pressure through the low pressure port?

[ 08-10-2004, 12:58 PM: Message edited by: mdregister ]

[Mark Krieger]

You're on to a secret...

The pressure on the low-pressure side determines the temperature delivered out of the vents! A lower pressure will deliver a lower temperature and SOMETIMES bleeding off can improve things. For this reason, a GM compressor will cycle off when the pressure gets too low to avoid freezing the evaporator. You'd like to see it operating just above the point where the compressor trips off.

But there's more...

The pressure on the high side determines how hot the condenser gets too. It needs enough pressure to raise the heat of the evaporator above the outside air temperature so it can release energy into the atmosphere. Higher presser is better as long as it isn't so high it threatens to rupture the system.

If you bleed off too much R-134 and it lowers the high pressure too, you've actually made the system work worse.

The difference between high pressure side and low pressure side is the key.


Another interesting fact...

It's illegal to release refrigerant to the atomosphere, right?

Consider this: R-134A (1,1,1,2-TETRAFLUOROETHANE) is the same chemical that's used in "Duster Spray" (1,1,1,2-TETRAFLUOROETHANE) that's sold by the truckload. The law says you can't release REFRIGERANT to the atomosphere but you can chase dust-bunnies all day long.

[catmandoo]

i believe it's just illegal for the r-12,if its illegal for all refrigerant why can you go to wal-mart and you can buy the 134a for 1.99 a lb and the hose to fill it. i thought you had to be certified and trained for removal and filling the systems,there is a gm dealer here in iowa that sells r-12 for 600.00 for a 30 lbs can,wholesale,and at that price i don't know why anybody would want to use it..anyway back to the subject at hand,you say 90 degrees ,what was the humidity,it will affect output temp.still sounds like you might have some blockage in the oriface,did it get changed?any time we drained one it got a new one period,those r-4 compressors were junk to begin with and fly apart at will,they should have stuck with the a-6,big but rarely gave up the ship.i don't even know what they were thinking,like 10 lbs of weight savings was gonna help a 5000 lb suburban get better milage jeezus, come on.
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