Orifice tubes

[Scooterwrench]

I recently replaced the compressor in ol Smoky with one of those scroll types and while I was at it I changed the orifice tube from the original black/white GM .072" to the red Ford .062" These scroll compressors don't flow as much as as the R4 piston type and now I'm wondering if I should put the .072 back in there.
Before I changed out the leaking compressor my air temp at the center vent was 38deg at idle and now the best I can get is 42deg and it seems like it takes a few minutes to get there. Only changes to the system are the compressor,new accumulator/drier,new manifold hoses,the red orifice tube and charged it with r134a. The day I charged it the temp. was about 92deg so I ran the high side up to 275psi,low side was around 50psi at idle.
And yes I evacuated it for better than an hour.

 

[L31MaxExpress]

I recently replaced the compressor in ol Smoky with one of those scroll types and while I was at it I changed the orifice tube from the original black/white GM .072" to the red Ford .062" These scroll compressors don't flow as much as as the R4 piston type and now I'm wondering if I should put the .072 back in there.
Before I changed out the leaking compressor my air temp at the center vent was 38deg at idle and now the best I can get is 42deg and it seems like it takes a few minutes to get there. Only changes to the system are the compressor,new accumulator/drier,new manifold hoses,the red orifice tube and charged it with r134a. The day I charged it the temp. was about 92deg so I ran the high side up to 275psi,low side was around 50psi at idle.
And yes I evacuated it for better than an hour.

It is the scroll compressor they are known to have poor output at low rpm. A 0.071 would just blow warmer air. Might help to use an even smaller tube with that scroll. A 0.057" or 0.047". Your low side needs to get under 40 psi, preferably into the 30s for it to cool the best. What are your pressures at 2,000 rpm?

 

[L31MaxExpress]

Just looked. Orange is 0.057, Brown is a 0.052 and Green is a 0.047". If the 0.062 is not dropping below 50 psi I would try a 0.052" first. Less flow but more pressure differential creating a larger Delta T and lower temperature of the boiling gas in the evaporator core will result in more cooling especially at low rpm. I tested an 0.057 in my 97 van and it had great idle cooling but caused the compressor to cycle much more frequently at highway speeds even with the rear unit running and thus less cooling.

 

[Scooterwrench]

Just looked. Orange is 0.057, Brown is a 0.052 and Green is a 0.047". If the 0.062 is not dropping below 50 psi I would try a 0.052" first. Less flow but more pressure differential creating a larger Delta T and lower temperature of the boiling gas in the evaporator core will result in more cooling especially at low rpm. I tested an 0.057 in my 97 van and it had great idle cooling but caused the compressor to cycle much more frequently at highway speeds even with the rear unit running and thus less cooling.

Thanks man!
Your explanation makes more sense to me. I was surfing the interweb last night and they were saying more flow makes the evaporator colder hence the reason for the orifice tube,to reduce flow through the evap.
Another question for ya. Would placing the orifice in the inlet to the evap work better than having it way out front at a condenser outlet? Seems to me some cooling is lost going through that long metal tube before it gets to the evap. Or maybe putting foam tube(Armaflex)insulation over it? It only has a thin plastic covering now.

 

[L31MaxExpress]

Thanks man!
Your explanation makes more sense to me. I was surfing the interweb last night and they were saying more flow makes the evaporator colder hence the reason for the orifice tube,to reduce flow through the evap.
Another question for ya. Would placing the orifice in the inlet to the evap work better than having it way out front at a condenser outlet? Seems to me some cooling is lost going through that long metal tube before it gets to the evap. Or maybe putting foam tube(Armaflex)insulation over it? It only has a thin plastic covering now.

I think the difference there is minimal as long as the line is well insulated. My 99 Tahoe has a thick layer of factory foam insulation from where the orifice tube sits in the line on the inner fender to the evaporator core.

I do insulate the accumulator and suction hose. Some claim it makes no difference but the cooler the gas getting back to the compressor, the cooler it runs and the less heat the condenser has to deal with.

 

[Scooterwrench]

I do insulate the accumulator and suction hose. Some claim it makes no difference but the cooler the gas getting back to the compressor, the cooler it runs and the less heat the condenser has to deal with.

I always wondered about that. I was taught that you wanted to allow the freon to completely revert back to gaseous state before it enters the com. so it's not trying to compress a liquid. Then later I started seeing factory accumulators with insulation on them. I don't think I need to do it to mine the low side of the comp. sweats. This comp. runs really cool.

 

[PlayingWithTBI]

WARNING WARNING WARNING - THREAD HIJACK (momentarily). I just blew up my A/C today. IT was blowing nice and cold then, I stopped for gas, after I restarted the engine it started getting warmer until it blew hot air. When I got home, my R4 compressor wasn't turning so, I threw the gauges on it and the high side showed ~275 PSI while the low side actually showed a vacuum. Tomorrow I'll check it to see what happened, if I can. Anyway I ordered a new compressor, receiver/dryer, O-rings, system flUsh, and the white AC Delco orifice tube. That's why I jumped in - to see what rube I should get for my 88 C1500.

YOU MAY NOW RETURN TO YOUR REGULARLY SCHEDULED PROGRAM...

 

[L31MaxExpress]

WARNING WARNING WARNING - THREAD HIJACK (momentarily). I just blew up my A/C today. IT was blowing nice and cold then, I stopped for gas, after I restarted the engine it started getting warmer until it blew hot air. When I got home, my R4 compressor wasn't turning so, I threw the gauges on it and the high side showed ~275 PSI while the low side actually showed a vacuum. Tomorrow I'll check it to see what happened, if I can. Anyway I ordered a new compressor, receiver/dryer, O-rings, system flUsh, and the white AC Delco orifice tube. That's why I jumped in - to see what rube I should get for my 88 C1500.

YOU MAY NOW RETURN TO YOUR REGULARLY SCHEDULED PROGRAM...

Red 0.062, (Yellow 0.062 if evaporator mounted) is what I typically see the best results with on GMs.

The only way that is possible is a restriction in the system and likely it is the orifice tube from a compressor coming apart internally.

 

[Scooterwrench]

WARNING WARNING WARNING - THREAD HIJACK (momentarily). I just blew up my A/C today. IT was blowing nice and cold then, I stopped for gas, after I restarted the engine it started getting warmer until it blew hot air. When I got home, my R4 compressor wasn't turning so, I threw the gauges on it and the high side showed ~275 PSI while the low side actually showed a vacuum. Tomorrow I'll check it to see what happened, if I can. Anyway I ordered a new compressor, receiver/dryer, O-rings, system flUsh, and the white AC Delco orifice tube. That's why I jumped in - to see what rube I should get for my 88 C1500.

YOU MAY NOW RETURN TO YOUR REGULARLY SCHEDULED PROGRAM...

Sounds like your comp. blew up and now its innards are in the orifice tube screen. Is yours accessible through the right hand parking light opening too?

 

[PlayingWithTBI]

The only way that is possible is a restriction in the system and likely it is the orifice tube from a compressor coming apart internally.

Yeah, that's what I'm thinking too.

Sounds like your comp. blew up and now its innards are in the orifice tube screen. Is yours accessible through the right hand parking light opening too?

Mine is inline to the evaporator near the wheel well. I don't have a recovery system so, I thought maybe I'd wait for my son to come over AGAIN this weekend I must say, he's been treating his Old Man well lately - i used to have to chase him around the house to get anything done