AC Connector

With pleasure Sir =) The flow of refrigerent is dependant on head pressure and wether it is vapor or liquid. This flow is measured in lbs/min. Let's say you are driving down the road at 55-60 MPH and your AC is cranking out the cold air and everyone is nice & comfy. Now we come to an exit, slow down or even stop at an intersection. For a short time there is much more refrigerant flowing from the condenser than is flowing to the condenser. This causes the liquid to be flushed from the condenser, after which some vapor flows from the condenser as well. With lower engine RPM (less pressure) and less air flow through the condenser less cooling is taking place in the condenser and it cannot create enough liquid to keep the evaporator flooded and the temperature of the air passing through the evaporator rises. Now here comes the tricky part. Flow is measured in lbs of refrigerant/minute, yes? Liquid has more mass (weight) than vapor, yes? OK, so a condenser full of vapor contains less refrigerant than a condenser full of liquid. By reducing the flow of the refrigerant vapor (smaller orfice) the condenser has a chance to catch up and deliver liquid to the evaporator, not to mention that the accumulator can again provide a more or less steady flow of expanded (we are on the low side now remember) liquid to the evaporator. An important side result is that it is the liquid, not the vapor, that carries oil to the compressor.

So low speed or idle, smaller orfice helps maintain liquid in the evaporator and the system produces colder air.

The down side is at highway speeds the orfice might be too small and the compressor could be damaged by too high a head pressure. This is why I advised the OP to use a variable orfice valve in his converted AC system in his 95 Tahoe. I would have one in my Yukon except I have rear air.

Regards, JR

"Stormin Mormon" wrote in message news:w8%fr.155545$ snipped-for-privacy@news.usenetserver.com...

Some people just have minds that handle other types of information. it's very possible that some people "just don't get it" but excell in other areas.

Christopher A. Young Learn more about Jesus

Trying to explain how things work to people who don't work with it can get interesting. Try explaining electron flow in a circuit some time.

I remember being the glass eyed one on a few occasions.....

With pleasure Sir =) The flow of refrigerent is dependant on head pressure and wether it is vapor or liquid. CY: Also depends on orifice, and the evaporator low side pressure.

This flow is measured in lbs/min. Let's say you are driving down the road at 55-60 MPH and your AC is cranking out the cold air and everyone is nice & comfy. Now we come to an exit, slow down or even stop at an intersection. For a short time there is much more refrigerant flowing from the condenser than is flowing to the condenser. CY: I don't know if this happens, or not. Lets presume that it does.

This causes the liquid to be flushed from the condenser, after which some vapor flows from the condenser as well.

CY: That is possible. So, tell me, does the vehicle in question have an accumulator? Also called a receiver, in refrigeration speak?

With lower engine RPM (less pressure) and less air flow through the condenser less cooling is taking place in the condenser and it cannot create enough liquid to keep the evaporator flooded

CY: Flooding the evaporator is not desirable. Cooling works best when there is a liquid to vapor flash, not a flooded evaporator.

and the temperature of the air passing through the evaporator rises.

CY: Actually, the temp also rises, if you flood instead of flash. I think you're writing that a lower feed of refrigerant will result in higher evaporator output temps.

Now here comes the tricky part. Flow is measured in lbs of refrigerant/minute, yes?

CY: Been a while since I've needed that info. But pounds per minute sounds reasonable.

Liquid has more mass (weight) than vapor, yes? OK, so a condenser full of vapor contains less refrigerant than a condenser full of liquid.

CY: That isn't necessarily so. You can have the same mass of refrigerant in the condensor, in liquid or vapor. Depends on the temperature.

By reducing the flow of the refrigerant vapor (smaller orfice) the condenser has a chance to catch up and deliver liquid to the evaporator,

CY: With small orifice, yes, the condensor has a chance to catch up. On the other hand. Wiht the larger orifice, the discharge from compressor will be a higher temperature, and you'd get more cooling from the condensor, compared to the smaller orifice. Higher temp means more delta T, and more BTU are moved.

not to mention that the accumulator can again provide a more or less steady flow of expanded (we are on the low side now remember) liquid to the evaporator.

CY: What is "expanded liquid"? Can't say as I've heard of that.

An important side result is that it is the liquid, not the vapor, that carries oil to the compressor.

CY: I thought it was both.

So low speed or idle, smaller orfice helps maintain liquid in the evaporator and the system produces colder air.

CY: As above. Larger orifice, more refrigerant flow, and more hot refrigerant going into the condensor.

The down side is at highway speeds the orfice might be too small and the compressor could be damaged by too high a head pressure.

CY: In a saturated, air free system, head pressure should be dependant on discharge temperature.

This is why I advised the OP to use a variable orfice valve in his converted AC system in his 95 Tahoe. I would have one in my Yukon except I have rear air.

CY: So, tell me what a variable orifice valve is, and how it works?

Regards, JR

CY: I still think that smaller orifice means less refrigerant flow, and less cooling.

Your arguements for your position are getting a bit esoteric to the discussion. We are talking about an AC system in a more or less modern car/truck. but to answer your question vis a vi a VOV. A variable orfice valve replaces the stock fixed orfice valve in a GMC for instance. as the truck travels down the highway with AC running, condenser condensing, accumulator accumulating, evaporator evaporating and all is right with the world. The pressure of the liquid refrigerant leaving the condenser pushes on a spring loaded piston opening a nice fat orfice. (about .070-.075") When you slow down or stop as discussed before, the pressure on the piston is reduced and the spring pushes the piston back against the flow to either partly block the big orfice, or totally block the big orfice and uncovers a smaller (usually

This is what you are explaining: ============================== I do however stand by my statement that at lower city driving speeds or at idle a smaller orfice will help keep the cabin air cooler precisely because it DOES allow more refrigerant to circulate thru the system. ==============================

OK, how does a smaller orifice lead to more refrigerant flow?

Is that valve similar to the TXV that stationary refrigeration systems use?

Been a while since I worked on a car AC, but they typically have a couple pounds of refrigerant. Enough to keep accumulator with some liquid in it.

Christopher A. Young Learn more about Jesus

"JR" wrote in message news:BbidnabpY60sUx3SnZ2dnUVZ snipped-for-privacy@ptd.net... Your arguements for your position are getting a bit esoteric to the discussion. We are talking about an AC system in a more or less modern car/truck. but to answer your question vis a vi a VOV. A variable orfice valve replaces the stock fixed orfice valve in a GMC for instance. as the truck travels down the highway with AC running, condenser condensing, accumulator accumulating, evaporator evaporating and all is right with the world. The pressure of the liquid refrigerant leaving the condenser pushes on a spring loaded piston opening a nice fat orfice. (about .070-.075") When you slow down or stop as discussed before, the pressure on the piston is reduced and the spring pushes the piston back against the flow to either partly block the big orfice, or totally block the big orfice and uncovers a smaller (usually

Yep, This is also why higher education is a waste of time for some people.

The system is barely adequate for the size of the explorer interior (Here in sunny Arizona) so I didn't convert. Instead I used A product called ES-12a, I think it's mostly propane. Seems to work as good as the R12 did. I've also used Freeze-12 in one vehicle and it worked ok. My car's that came from the factory with 134a I stick with that.

I just got a 2000 Malibu and the AC in it didn't seem quite up to snuff so I evacted it and recharged it with some stuff that supposed to be some superduper synthetic 134a+ that will cool better then regular 134a. We'll see how that does.