A/C questions

[CamoChevyK10]

Gotta 1979 k10, it HAD factory A/C. One of the previous owners removed compressor an stripped out all the emissions crap an vacuum canister thats on driver side. Question is do i need that vacuum canister for the compressor to take the coolant? Cuz i borrowed the compressor of my dads 79 k10. Identical trucks.... hooked lines up, put on a belt, an plugged up wiring harness, wouldnt take the freon. Now in the cab the vacuum lines under dash are in pretty rough shape. Dry rotted an a few are broke. But that dont matter right? Those inside only control the doors in duct work right? An they dont work without the canister either? Right? Lol any advise would be great. Cuz my cuzin gotta 84 K10 that he making into mud truck an is getting rid of A/C, the canister an other crap he dont need. He offered it all to me for free. Anyways thanks for any help yall!

 

[chengny]

That spherically shaped chamber is the vacuum reservoir (see the attached) - and you're right; it is only part of the air flow control system.

It's there to provide a back-up vacuum supply when none is available at the intake manifold (i.e. when the throttle is wide open).

It is not associated with refrigeration part of the A/C system.

The reason you cannot add any refrigerant to the system is because (and this is going to sound counter-intuitive) there is no refrigerant in the system.

This is a simple explanation of how your A/C system controls the compressor. Without the compressor to running (which creates a low pressure area in the suction piping) you can't get enough 134a out of the can and into the piping:


Control of the refrigeration cycle (on and off operation of the compressor) is done with a switch that senses low side pressure as an indicator of evaporator pressure. During air temperatures of 60-80°F, the equalized pressures within the charged air conditioning system will close contacts of the pressure switch.

When an air conditioning mode is selected, voltage is supplied to the compressor clutch coil. As the compressor reduces the evaporator pressure to approximately 25 psi , the pressure switch will open, de-energizing the compressor clutch. As system equalizes and the pressure reaches approximately 46 psi , the pressure switch contacts close, re-energizing the clutch coil.


Anyway, here is how to fool the system into starting the compressor for long enough that the LP switch will take over and you can add normally.

On the filter drier there is a switch (the low pressure switch). Thee is a pair of wires attached to the terminals of the switch. Pull the connector off and jump across the female terminals of the connector - do this with the engine running. The comprssor clutch should pull in and the compressor will start pumping. After a minute or so the suction line will be under a vacuum and at that point you can start adding gas to the system.

I think your truck takes about 4-5 cans of refrigerant total.

After you get 2 or 3 in the system you can remove the jumper and reconnect the wring connector to the switch. It should accept the remainder of the charge without overriding the switch.

 

[CamoChevyK10]

Ohhhhh ok. Lol i really appreciate it man. Lol gonna need some a/c, done drove it almost 3 years without an i aint going without it this summer. Haha but thanks man

 

[oneluckypops]

That spherically shaped chamber is the vacuum reservoir (see the attached) - and you're right; it is only part of the air flow control system.

It's there to provide a back-up vacuum supply when none is available at the intake manifold (i.e. when the throttle is wide open).

It is not associated with refrigeration part of the A/C system.

The reason you cannot add any refrigerant to the system is because (and this is going to sound counter-intuitive) there is no refrigerant in the system.

This is a simple explanation of how your A/C system controls the compressor. Without the compressor to running (which creates a low pressure area in the suction piping) you can't get enough 134a out of the can and into the piping:


Control of the refrigeration cycle (on and off operation of the compressor) is done with a switch that senses low side pressure as an indicator of evaporator pressure. During air temperatures of 60-80°F, the equalized pressures within the charged air conditioning system will close contacts of the pressure switch.

When an air conditioning mode is selected, voltage is supplied to the compressor clutch coil. As the compressor reduces the evaporator pressure to approximately 25 psi , the pressure switch will open, de-energizing the compressor clutch. As system equalizes and the pressure reaches approximately 46 psi , the pressure switch contacts close, re-energizing the clutch coil.


Anyway, here is how to fool the system into starting the compressor for long enough that the LP switch will take over and you can add normally.

On the filter drier there is a switch (the low pressure switch). Thee is a pair of wires attached to the terminals of the switch. Pull the connector off and jump across the female terminals of the connector - do this with the engine running. The comprssor clutch should pull in and the compressor will start pumping. After a minute or so the suction line will be under a vacuum and at that point you can start adding gas to the system.

I think your truck takes about 4-5 cans of refrigerant total.

After you get 2 or 3 in the system you can remove the jumper and reconnect the wring connector to the switch. It should accept the remainder of the charge without overriding the switch.

That was all very well said.
Only thing I would have mentioned is: You NEED to have the System Vacuumed down BEFORE you start jumping the switch. With out having it sucked down your doomed to have higher pressures, plus its going to be harder then hell to get the system fully charged with air in the system...

 

[chengny]

That was all very well said.
Only thing I would have mentioned is: You NEED to have the System Vacuumed down BEFORE you start jumping the switch. With out having it sucked down your doomed to have higher pressures, plus its going to be harder then hell to get the system fully charged with air in the system...


You are right - and I realized, while writing the reply, that I should also include all the basic steps that are required before charging a newly installed system.

But to go into detail about everything would have taken forever. At a minimum we would need to discuss:

1. Component flushing

2. Assembly of components (with new o-rings of the correct type)

4. Necessity of a new filter/drier

5. Initial evacuation procedure

6. System integrity/leak down testing

7. Pre-charging with proper type/quantity of oil


But I can't touch type - I have to look down at the board for each key stroke - and it was late.

Not only that, but not many people have a vacuum pump (with the proper fittings) just hanging around the garage.


If anyone reads this and needs to purge a system of non-condensables (fancy term for air), but have no access to a deep vacuum pump, try the following. It is a real "old school" method. It displaces most of the air, but won't get all the moisture out and so it definitely requires the installation of a new filter drier:

After assembly, and initial refrigerant charge, get the system running on it's own. Due to the fact that the components and inter-connected piping were never evacuated there will be significant quantities of air in the system.

The air will become entrained with the refrigerant and flow along with it - until it gets to the condenser. In the condenser, cool air (flowing over the outside of the coils/fins) causes the hot refrigerant gas that comes in from the compressor to return to a liquid and precipitate out. It then falls to the bottom of the condenser.

Now the important part.

In the condenser, while the refrigerant can be cooled and changed back into a liquid, air retains it's gaseous state. Any air that enters along with the refrigerant cannot be condensed - hence the term "non-condensable".

As the refrigerant is cooled (condensed), it forms into droplets and falls to the bottom of the condenser. From there it flows through the high side piping and (via the metering device/orifice) enters the evap.

Anyway, back to the air that did not condense. Because it is lighter than the refrigerant vapor, it separates and rises to the top of the condenser.

After enough air is collected in the condenser, it begins to impact the cooling/condensing capacity of the heat exchanger.

Here's how to bleed the air out.

Run the A/C for an extented time and shut down.

Crack open the fitting on the tubing that connects to the top of the condenser. Without a CFC leak detector you will be doing this blind - nothing bad will happen but you may waste some refrigerant. Let the gas slowly escape for a minute or so and the retighten the tubing fittng.

Do this several times after assembly. You can stop when there doesn't appear to be any further improvement in system operation.

Keep in mind that you may be dumping some of the refrigerant along with the air, so be sure to keep the system fully charged.