WEIRD HVAC BEHAVIOR ????

bugdewde · Aug 23, 2019

Yes, I have those pages from the service manual …. I was having issues id-ing the lines.
Removed the air cleaner intake box for a better look...…

DUH!!!!
I FORGOT I've got a rear air Suburban. The condenser line splits off into a "Y" and both go back to the evaporators (one in dash, one in rear) ….. so there appears to be two inline orifice tubes/nuts (one at extreme left of pic & one at extreme right of pic) …. and two larger return lines.

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I'm assuming the rear evaporator has it's own accumulator/dryer in back … as the 2nd larger line goes straight to the compressor from where I can see under the hood.

east302 · Aug 23, 2019

I was about to edit my post, I forgot you had the rear air as well.

If the rear has the thermal expansion valve instead of an orifice tube, it won’t need an accumulator for that segment. The accumulator is needed when an orifice tube is used. I think that’s right - maybe doublecheck.

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bugdewde · Aug 23, 2019

Looks like my '95 evaporator tube locations are reversed from yours.
Auxiliary tube is the upper one.
Main is the lower.

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Chart "A" states
"Feel liquid line before Orifice Tube" .
- Cold is a restriction.
- Warm, compare evap inlet & outlet temp.

__ My upper tube (auxiliary) is cold after the tube (assuming the tube is at the battery).
__ My lower tube (main) is hot all along the inner fender. Assuming it's tube is at the rear under the accumulator.

I thought the high pressure liquid line was supposed to be cold after the tube. The main line is hot after the tube (under accumulator). I'll post a video showing this.

But front and rear A/C both blow cold.

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bugdewde · Aug 24, 2019

I'm getting quite frustrated...... I really want to learn this system.

bugdewde · Aug 24, 2019

east302 said:
...... If the rear has the thermal expansion valve instead of an orifice tube, it won’t need an accumulator for that segment. The accumulator is needed when an orifice tube is used. I think that’s right - maybe doublecheck.

There's no mention of a Thermal expansion valve in the '95 manual pics... Not even in the glossary.

east302 · Aug 24, 2019

See if the manual has a diagram for the rear air components in the back. The TXV should be on the evaporator inlet back there. I see this parts diagram for 95, the expansion valve is #23:

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To me, when the manual says “before the orifice tube” it refers to flow direction - the upstream side or the side coming from the condenser. From what I read, the junction block or tee on the evaporator line after the condenser will have two lines going out. One will have the nut where the orifice tube is for the front evaporator and the other line (for the rear) will not.

Mine (both 98s) do not have rear a/c so the orifice tube is down at the condenser. But the connections to the front evaporator would, I would think, be at the same location on the firewall to allow parts sharing across different C/K platforms. They are right above the heater core lines on mine. The diagram in my earlier post showing the front evaporator line seems to bear that out. Your 95 diagram does as well, though the text doesn’t seem to agree. I’d look for the evaporator line with the nut or union after the tee. That should allow access to the orifice tube, meaning that it has to be the line to the front evaporator.

It’s for a 2001, but this system diagram is how I’d interpret the flow path on a rear air Suburban...

https://www.performancetrucks.net/f...ce-21/ac-system-rebuild-2001-suburban-530240/

Edit: Cliffs Notes version, I think the orifice tube is at the union (circled in red), the front and rear lines marked as F and R in your video.

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bugdewde · Aug 24, 2019

east302 said:
Edit: Cliffs Notes version, I think the orifice tube is at the union (circled in red), the front and rear lines marked as F and R in your video.

Yep, east302.... you're right.
Thanks for jogging my mind loose from going on what my manual stated.... it was in plain view.

I can trace the line from condensor to firewall evap (front ac).
But it's labeled as "Auxiliary Evaporator Tube Location" in Figure 47 .... See large black arrow.

Misleading, as I assumed "auxiliary" meant rear.... Hmmmmmm.... But it clearly goes to firewall, not down the frame rail like the other one.

So I would assume the orifice would be at that union nut.... As it's Hot upstream and Cold downstream.
_____________________________________________

The rear assembly shows no breakdown of internals like yours. Figures 54 & 55.
So I assume the rear orifice is near the union nuts on evap linexrunning down the frame rail (one piece).... Either at firewall below accumulator or at the base of the rear evap.

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_____________________________________________

No mention of Thermal Expansion Valve (TXV) anywhere like yours.... (Not even in the glossary).

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Haven't seen any leaks .... Appears to have yellow dye in system.

bugdewde · Aug 24, 2019

I traced the rear line down the frame rail (it appears to be one piece). Appears the union nuts are just below the accumulator (my finger) and at the evap in the rear.
MAYBE, the orifice tube is at either one????

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_____________________________________________

The rear

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Now that I may have the major components/ lines figured out ..... Gotta recheck all the names/locations of the switches again.

East302, My pressures were pretty close to his in the link you provided. Im using same gauges. Maybe I shouldn't be using the red scale (134a) for pressure readings.... Maybe just for static numbers?

bugdewde · Aug 24, 2019

I found this yesterday googling another member's issue with his "knocking" AC compressor issue.

A poster says the '94-95 Suburbans with rear air used a TXV in rear. ... or 2 orifice tubes.
No need for a rear accumulator, as the long large diameter return line acted as an accumulator & collected oil/liquid.

Some of these guys seem to know AC pretty well. But appears to be 6.2 & 6.5 diesel forum.

https://www.thetruckstop.us/forum/t...s-it-has-a-thermal-expansion-valve-txv.23287/

bugdewde · Aug 24, 2019

andy396 said:
First easy and cheap thing to try would be the low pressure cycling switch on the accumulator/dryer. It’s like $15 and can be swapped in the parking lot.

So …. may have to try this ....... since my compressor stays engaged all the time now, at idle …… the switch might be stuck in the closed position.... causing the compressor to engage continuously . This might cause the higher than usual low-side pressure I'm seeing.

WEIRD HVAC BEHAVIOR ????

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