[Jase007]

Is your auto AC system a mystery?

Doesn’t have to be.

Here is a basic write-up on how it works:

Refrigerant flow as described by Prof.

(1)Compressor draws LOW PRESSURE HOT VAPOR refrigerant from the evaporator (suction port - large line), and compresses the vapor.

(2) HIGH PRESSURE HOT VAPOR from the compressor goes into the condenser. The vapor gives up its latent heat to the cooler outside air through the condenser and changes back to LIQUID (like steam back to water). Now its a HIGH PRESSURE LIQUID.

(3)The HIGH PRESSURE LIQUID now encounters an orifice (small opening) either an orifice tube or expansion valve. When the liquid squirts through this opening, its pressure is reduced and it gets very cold.

(4) The now LOW PRESSURE COLD LIQUID absorbs heat from the cab through the evaporator and the liquid inside turns into vapor (boils) (like water absorbing heat and turning to steam) except refrigerants boil at very low temperatures.

(4a) Note: If the orifice is an O-tube, under some conditions too much refrigerant might get into the evaporator and not all boil. An accumulator is hooked on the evaporator output to "accumulate" this excess liquid and prevent the liquid from reaching the compressor.

(5) This LOW PRESSURE HOT VAPOR from the evaporator is now drawn into the compressor. Back to step 1.

Another version:

Hot compressed gas leaves the compressor via the small hose (aka high side hose) and enters the top of the condenser where it will cool off a little and "condense" from a hot gas to a high pressure liquid refrigerant.

Refrigerant exits the bottom of the condenser, and heads towards the evaporator as a high pressure liquid. To get the refrigerant to boil, and absorb the heat from the inside of the car, we need to turn that high pressure liquid into a low pressure boiling liquid. That refrigerant pressure drop happens right before the refrigerant enters the evaporator via an expansion valve or an orifice tube. This is the pressure split. The refrigerant enters the evaporator as low pressure mix of boiling liquid and vapor. Heat load on the evaporator changes the liquid to a gas vapor. This low pressure vapor then returns to the compressor (via the suction hose) to start the cycle over again.

My recent work:

1999 GMC Suburban AC repair.

Problem: leaked out R134a from compressor and high and low side service ports (Schrader valves). This repair is identical for ’96-99 Tahoe / Suburban and very similar for 2000 – 2006 GM Yukon / Yukon XL / Suburban / Astro VAN, etc…. Rear air option on mine and all Suburbans: C69 (inside on label in glove-box).

Front system is CCOT (Cycling Clutch Orifice Tube) – using an orifice tube (OT) and accumulator. Rear system uses a thermal expansion valve (TXV). There are two evaporators (front and rear), one compressor, one condenser, one OT, one TXV.

I (and a couple of hundred thousand other GM vehicle owners) have the notorious HT6 “belly leaker” compressor. Mine went T-up after 12 years of mild to heavy use in Mid-Atlantic area. I decided I would do the R&R myself after pricing the job out around $2,000+ from shops.



Things you need and can use again on any other R134a AC equipped car/vehicle:

AC Manifold Gauges: FJC 6761 R134a


Vacuum Pump: FJC 3.0 CFM Twin Port Vacuum Pump


Flush Bottle: Interdynamics FK-1 Air Conditioning Flush Kit for R-134a R-12 and R-22


O-Ring assortment: Advanced Tool Design Model ATD-356 270 Piece HNBR R12 and R134a O-Ring Assortment


PAG oil (viscosity depending on spec) FLAP

R134 refrigerant FLAP

Can Tap: Mastercool 85510 R134a Can Tap Valve-Screw-On Model


Parts specific to ’96-99 Suburban:

Accumulator (C69 Option with Rear air) ACDelco 15-1784


New HT6 Compressor (ACDelco / Delphi):15-22124A Air Conditioning Compressor


Condenser:ACDelco 15-6958 A/C Condenser


Hose ACDelco 15-30883 A/C Accumulator to Compressor And Condenser Hose


Orifice Tube (specific to C69 option with rear air): ACDelco 15-5612 Condenser Orifice



Procedure:

If system isn’t empty, have a shop recover the R134a. If it is gone already (as verified by gauges) open it up.

After removing the front of my truck to access the condenser and connections to AC hoses to compressor, rear air and front evaporator:



I accessed the front condenser (replaced) by removing some braces and lowering the cooler. (condenser removed here, seeing new radiator)



Modern parallel flow condensers are VERY difficult to flush out, better to replace for a couple of $$. (info HERE)

Disconnected the condenser:



Next remove the AC hose / pipe that contain the OT for the Suburbans, and also splits the R134a to the front and rear air systems (known as a “Y” pipe in GM truck owner speak).



Connection at evaporator (above and to left of heater hoses into heater core):





Disconnect low and high side lines that run to the rear evaporator and TXV.



DECISION TIME: 99% of the connections at the rear evaporator on Suburban / Tahoe are frozen by galvanic action of disparate metals. Nearly 100% of people destroy the rear evaporator aluminum hardlines when trying to break the connections to the under truck lines that terminate in the engine bay (above picture). Most shops won’t touch these.

My suggestion: IF you have NOT had a catastrophic compressor failure and your dye testing has proven the lines to the rear and the rear evaporator are intact … THEN leave it alone. Break open the connections in engine bay (see above pic) put a plastic sandwich bag over the open lines to the rear and keep working on the front.

You’ll have to approximate how much oil remains in the rear evaporator and lines but .. you won’t have to 1.) attempt to disconnect the AC lines to the rear AC evaporator and 2.) remove rear AC unit or cut an access panel (through plastic) into rear AC unit to remove / replace TXV for flushing.

I did not flush lines to the rear AC. I did not break open connections from rear lines to TXV and evaporator.

I lost R134 and system would work with a charge ..but wouldn’t hold R134 for more than a couple of days. My dye testing showed belly leaker HT6 compressor and leaking high and low side service ports.

Disconnected/removed the low side cut-off switch connection and accumulator:



What remains (can see dye in R134 at evaporator inlet and outlet):



Remove AC hose from accumulator to compressor to condenser. Aluminum block on top of compressor has a center bolt on my year:



Transfer switch from back of old compressor to new (need snap ring pliers, pulls out):



Installed:



My new compressor shipped dry. Check and remove any left over oil so that you get proper amount in system. This generation of Suburban / Tahoe with rear air takes 11 oz of PAG 150.

Installed compressor (be careful torqing aluminum ears down on bracket):



I flushed my front evaporator with the compressed air bottle and AC flush fluid from Interdynamics (China via Advancedauto.com). I flushed any hard lines {“Y” pipe) I reused. I flushed the front evaporator ~10 times and then once more. I ran compressed air through the evaporator on and off for the better part of an hour to get remaining solvent out of evaporator. In a perfect world with a high capacity air compressor … you should run clean dry shop air at min 50 psi through the evaporator for 30+ minutes post flush.

With evaporator cleaned, new condenser in, new OT in AC “Y” pipe, new manifold hose (accum to compressor to condenser) installed, new compressor installed it was time to add oil and button it up.

My system holds 11 oz PAG 150. Manuals suggested replacing ~8 oz (cumulative) when replacing compressor, accumulator, condenser, and all hoses (with mufflers on them) and pipes front of the firewall. The assumption is that ~ 3 oz remains in the lines to the rear, rear TXV and rear evaporator. Sounds reasonable.

New accumulator install and attached to new AC manifold hose (accu to compressor to condenser):



New LPCO (low pressure cut out) switch installed:



AC manifold hoses and switch installed on compressor:



** Be SURE to rotate compressor by hand several times to circulate new oil in the compressor before charging. You should add the bulk of your replacement or new PAG oil to the compressor if it was empty. I added at least 5 of the 8 oz to the compressor and then rotated several times.**

I used Nylog on all new O-rings at the connections and then I buttoned everything up, connected my AC hoses and the vacuum pump (new clean oil please in pump) and pulled a vacuum:



Left it this way for a few days to boil off moisture and ensure no leaks at this low pressure (14.7 psi - atmospheric). If I had a bottle of nitrogen and the correct regulators / connections, I’d have pressure tested the system to ~ 150 psi and see of it held as well. If I had a way to mix some nitrogen and R134 and then pressurize system while I checked with my non-existent electronic refrigerant “sniffer”, that would have been ideal.

Charged system up by weight with cans and was fortunate that my system takes 56-64oz of R134 depending on what manual you look at (love the exactness). Sticker on old accumulator called for 56oz of R134a. All manuals (Alldata, per Gm techs, etc…) called for 64 oz. I determined that 5 *12 net oz cans got me 60 oz (right in the middle). That is what I used. I can add to "fine tune" later but don't think it is necessary.

On a 87 degree day, vent temps are at 38F:



My gen suburban only has a mechanical fan clutch (replace these as they fail and don't draw enough air over condenser at idle). Year 2000+ GM SUVs all have an electrical puller fan over the condenser. I can add if needed but hasn't been necessary for 9 years of ownership ... even in hottest weather.

I did not go into charging your specific system (how to hook up gauges, purge lines, open or close high and low side knobs on the gauges) b/c you should read your manual or know / learn the proper way for your gauges. I think there are tips and tricks I forgot to include in this DIY but they may not be appropriate for all auto AC systems.

Haynes has a good technical manual for all vehicles up to 1999. Basics on auto HVAC are in there.

Good auto AC forum: http://acsource.net/acforum/index.php
Another with decent prices on parts: http://www.autoacforum.com/

The number 1 thing on repair of "opened" systems that have suffered a component failure is proper flushing of evaporator(s) and any retained hoses / pipe / connections. Contamination will quickly ruin new compressors, clog condensers, plug TXVs or OTs, etc...

Both front and rear AC systems now chill the cavernous interior right down to ice cold.

My total cost for all ACDelco parts and tools was less than $1,000.

Cheers.

[87turbolook911]

Nice write up!

[BlackTalon]

Jase is gunning for some more HOF posts

[Jase007]

Another improvement to "airflow" is to remove the front blower motor and clean out the front evaporator.

Typically on large 'mercan SUVs the blower motor is located on the lower right of the HVAC box under the dash. In GM vehicles you can see the round insulated cover (noise) just above the passengers feet.

Here is a step by step:

1. remove glove box for access and better visual.



2. remove rubber insulation over blower motor.

3. remove electrical connections (spade connectors) to fan

4. remove 6 or so bolts holding blower motor in to housing. Rotate blower motor so that flat part of casing is facing up and carefully remove so as NOT to damage the "squirrel cage" fan vanes.



You should be looking at this:



5. Look inside hole and up and to the left and you'll see the front of the evaporator:



6. get your shop vac and vacuum out all the debris (twigs, sticks, hair, dirt, etc...) before you start spraying water / cleaner in there.

7. get some old tooth brushes and some simple green and start spraying and scrubbing the fins on the evaporator (GENTLY!!). Rinse and repeat several times. Use a garden hose and carefully spray down evaporator between cleanings.

You'll learn VERY quickly if your evaporator tray vent hole/hose is clogged (access on firewall in engine bay). Mine drained right out on the ground ... don't overdo the rinsing (flood) the evaporator case.

8. Button back up and test blower motor is working and you should have a "clean. fresh, feeling" for another few years.

Notes:

Even though many newer full-sizers have cabin air filters, this is also a good idea to do if you have neglected to change the filters or you get a "musty" smell whenever you use AC or recirculate on your fresh/AC air from the cabin air.

There are "evaporator cleaner" sprays that will foam on and can be sprayed from a long tube ... unfortunately, they don't eliminate the crud that may have built up on the front of the evaporator (debris). If you can access and hand clean, will get better results.

This is what mine (above pic) looked like (not to bad) after 10 years of use, kids, etc...

Good luck.

[BlackTalon]

Tow Vehicle HoF

[94 Suburban]

Originally Posted by BlackTalon

Tow Vehicle HoF

Do you know anything about how to remove the interior trim and rear A/C evaporator on a '99 Chevy Tahoe?
Thanks.

[Jase007]

Don't know about Tahoe but ... if like the Suburban ... lots of pieces have to come out.

Also, MOST of the connections to the rear evaporator are frozen (disparate metals).... and new lines + new rear evaporator cost some $$$ for parts and labor.

See if the lines to the rear evaporator are even able to separate (brake loose) before continuing with repair.

[94 Suburban]

Originally Posted by Jase007

Don't know about Tahoe but ... if like the Suburban ... lots of pieces have to come out.

Also, MOST of the connections to the rear evaporator are frozen (disparate metals).... and new lines + new rear evaporator cost some $$$ for parts and labor.

See if the lines to the rear evaporator are even able to separate (brake loose) before continuing with repair.

Thanks, Jason. I figured as much, about the lines and disconnecting. Do you happen to have any exploded views of the interior or views of the rear evaportor compartment. I like to see what I am getting into and where I am going before I start repairs that I haven't done before.

[ChayydTayloor]

Thanks Mod Jase007 for Explaining in detail, Indeed very helpful for everyone here

Regards
Air Conditioning Service Phoenix Company