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AC questions and opinions

I did a little reading up on these r4 scroll compressors and found where their output at idle isn't that great. I think if I have to replace. I am going to attempt the sanden swap. found a few threads here on that. I do remember reading on the sanden here in the past and if memory serves me right, someone posted printable templates for the bracket to use when doing this swap but I haven't found them yet. there simply two flat plates of steel in a half moon shape with three holes drilled. I gotta keep digging around.
 
It seems that theferm may have done an article on A/C compressors.
I dont remember anything about the brackets though.
Possible to maybe drill new holes into the existing brackets if the housings diameter is the same between the two styles.
 
dbrannon79 said:
I am going to attempt the sanden swap.
Click to expand...

Brackets are for gasoline engines. The valve covers due to the "IDI" are taller vs. Compressor mounting bolt holes. The back of the Sanden compressor with the existing gasoline brackets will hit the valve cover.

More or less get a compete 1996+ Driver side compressor belt drive setup to eliminate the R4. May need to include the thermostat housing if I recall correctly.
 
WarWagon said:
Brackets are for gasoline engines. The valve covers due to the "IDI" are taller vs. Compressor mounting bolt holes. The back of the Sanden compressor with the existing gasoline brackets will hit the valve cover.

More or less get a compete 1996+ Driver side compressor belt drive setup to eliminate the R4. May need to include the thermostat housing if I recall correctly.
Click to expand...
This thought also crossed my mind, but I think I read somewhere that I would have to convert the single t-stat to a dual for it all to fit.

I was looking around on different sites and found that vintage air does make a kit for the r4 to sanden that's made for tall valve covers. it's the same half moon brackets but also has another bracket that mounts on the opposite side that raises the compressor. at work all of our road trucks use sanden compressors, since I'm the "parts" man in the shop I have access to one I can get some measurements from and possibly could get one of the welders in the shop to fab up some of these brackets. I downloaded a pic from a set online and printed it out. it seems to have printed close to the exact size, but I also am fairly good at photo editing where I can expand the image and plot measurements in the photo application to allow printing the image to the size I want. might be able to do a custom bracket blueprint that would work on these engines.

I'd also love to eliminate the block style connection for the suction / discharge manifold and have two seperate hoses that would have normal fittings where a person can easily make them from standard off the shelf fittings. if I dream too much I'd also try to use a dryer / accumulator from a 92 model where it has sae threads on the sensor ports. some of those accumulators had two ports where I would be able to move the charge port up where you can get to it without burning your hand on the turbo trying to charge it lol...
 
What are the symptoms of a bad variable orifice tube? I have been hearing a noise lately that seems to have gotten a little louder since this summer heat has come upon us. I haven't really done anything to the ac yet other than checking pressures, I do know that the high side will spike when you first turn it on and then slowly settle around 30 and 220 just low enough to turn off the fan clutch. Getting out on the road the compressor will cycle even in this 100+ degree heat. Vent temps will get down to around 50 but takes a while to get there, stays at 60 for a good 3-4 miles even with the compressor cycling a bit. (I had marked the pressure the cycle switch opens at once before at 26 psi).

today as I got home from work after shutting off the truck I heard the noise and stepped around to the front of the truck to listen. the noise is coming from where the orifice is in the condenser. it's making a sound like someone had pinched a balloon letting the air out just not as loud as the annoying balloon sound. I am assuming the pressures are equalizing between the high and low sides, but weird pitched buzz/squeal/humming normal? my wife even came out asking "what's that noise, what did you break now"
 
I found Sanden bracket on Ebay. Never used it, though.

www.ebay.com

General Motors R-4 to Sanden 508 A/C compressor adapter Bracket MADE IN USA | eBay

Replace your General Motors R4 pancake style air conditioner compressor to a Sanden 508 style compressor using this adapter.
www.ebay.com

www.ebay.com

Dirty Dingo R4 to Sanden 508 AC Compessor Conversion Mounting Bracket Kit | eBay

Dirty Dingo Sanden 508 7 Piston Compressor Billet Head With R4 Fitting Ports. Dirty Dingo Sanden SD7B10 Billet A/C Compressor Fitting - Flange Mount to O-Ring. This kit will allow you to install a more efficient Sanden 508 compressor into the factory R4 compressor bracket.
www.ebay.com
 
That first link is one I found also. I may go this route when this pancake compressor 💩's the bed!

I was searching the web today looking at 134a pressures to vent temps and came across this troubleshooting site (linked below). according to the pressures it shows compared to ambient temps outside, my system is low on 134a although I'm sure it's overcharged with about 40 oz or 3-1/2 cans! with 95-100 degrees outside and rpms up around a grand (high idle switch on) pressures are right at or a hair under 30 low and about 225 high, blower on max. holding at 2k to 2500k rpm will make the compressor begin to cycle dropping the low side down to 26 when the switch turns it off for a second or two.

I'm really skiddish of adding any more 134a. I really think there is something up with this vov orifice tube. I am leaning more and more towards evacuating and installing the oem fixed orifice tube then trying it again. only draw back is loosing all that 134a again!

maybe if I can fignagle my vacuum pump with exit port fittings so I can pump it all into a holding tank, plus weighing the tank before and after to see what I really had in there.

here's the link...
ricksfreeautorepairadvice.com

AC pressure gauge readings

How to diagnose car AC pressure gauge readings
ricksfreeautorepairadvice.com

and another link showing a pressure chart confirming my system is low!

AC System Pressure Chart - A/C recharge kits

rechargeac.com rechargeac.com
 
On this compressor, a lot of times the low pressure switch attached to the dryer is weak or bad.
The good news is, you can replace it without evacuating refrigerant.
Try replacing this part first since it is only less than $20 a few years ago.

Yes, the R-134 needs to be in the correct range of pressure to cool properly.
Too much is not good.
Did you put in more R-134 thinking that it is low?
That may be the cause of the problem.
Now you need to let some of them go out again.

Another tip, if you have some sort of threaded valve cover on the low pressure schrader valve, took it off.
That cause a leak somehow.
 
Last edited:
dbrannon79 said:
What are the symptoms of a bad variable orifice tube? I have been hearing a noise lately that seems to have gotten a little louder since this summer heat has come upon us. I haven't really done anything to the ac yet other than checking pressures, I do know that the high side will spike when you first turn it on and then slowly settle around 30 and 220 just low enough to turn off the fan clutch. Getting out on the road the compressor will cycle even in this 100+ degree heat. Vent temps will get down to around 50 but takes a while to get there, stays at 60 for a good 3-4 miles even with the compressor cycling a bit. (I had marked the pressure the cycle switch opens at once before at 26 psi).

today as I got home from work after shutting off the truck I heard the noise and stepped around to the front of the truck to listen. the noise is coming from where the orifice is in the condenser. it's making a sound like someone had pinched a balloon letting the air out just not as loud as the annoying balloon sound. I am assuming the pressures are equalizing between the high and low sides, but weird pitched buzz/squeal/humming normal? my wife even came out asking "what's that noise, what did you break now"
Click to expand...

The charge is either too low tripping the low side cut out switch ... Are BOTH evaporator pipes in/out nearly the same temperature of cold with the system running? Yes = likely an OK charge. (Not a low charge.) No with the going to the accumulator pipe warm = low charge no/low oil flow to compressor.

Too much charge or not enough condenser cooling airflow can trip the high side safety cut-out switch.
 
WarWagon said:
The charge is either too low tripping the low side cut out switch ... Are BOTH evaporator pipes in/out nearly the same temperature of cold with the system running? Yes = likely an OK charge. (Not a low charge.) No with the going to the accumulator pipe warm = low charge no/low oil flow to compressor.

Too much charge or not enough condenser cooling airflow can trip the high side safety cut-out switch.
Click to expand...
both the lines seem the same temp. even the liquid line on the inside of the radiator support feels the same coolness. the system doesn't have a high side cut out switch or at least the previous owner had eliminated it since there was no switch in the back of the compressor before. I used that port on the compressor to install the purple condenser fan switch. the only high side pressure switch that is on there is the one mounted on the condenser that I believe is for the recerc air motor.

here is what I have witnessed with my gauges connected. on first start up after the truck has been sitting in the hot sun and not running the high side pressure immediately spikes up to around 250, fan begins to roar, then rather quickly climbs up past 350 for about a minute or two. low pressure slowly drops from around 110 (off) to 70 - 60 - 55 beginning to cool from the vents.. then it seem that something opens up and the high side pressure begins to drop down back to around 275- 250 - 225 while the low pressure gets to around 30. at that point the vent temp gets colder, around 60 deg drawing in the hot cabin air still. usually takes about 10 minutes of idling like this and the vent temps will get to 50-55 ish temp and pressures seem to stay around 30 low and 210 - 225 and stay there.

if I hit the high idle switch during this above mentioned episode it all just happens faster and doesn't take as long to get to cooling as I would expect.

once pressures settle and it's cooling, taking the rpm to say 2500 the compressor will cycle with the low pressure dipping to the point it makes the cycle switch cut off the compressor. does the same on the road moving. by the way the fan clutch draws a hellofa lot of air !!!

what's got me puzzled is how it spikes in the beginning and then drops pressure and stays there to a point it acts like the VOV is just about closed and then opens fully allowing full flow of 134a making the system act like it's low charge. of coarse with the wired buzz/hum sound after you shut off the truck that can be heard in the cab and very pronounced if standing in front of the condenser as the pressures equalize!

I hope I explained what I am witnessing well enough lol
 
How often does the clutch cycle? Is the blower fan on high? At 2500 RPM, aka freeway speed, you are pumping a lot of refrigerant gas.

As you noted from a hot startup everything is HOT inside the cab including the evaporator. It takes a little time to move that heat from the evaporator to the condenser. The engine fan delay coming on doesn't help. I know you have a better setup than OEM and this should help.

It takes ~2 min for hot gas to quit condensing under the high pressure. You will, of course, hear the VOV hissing just like a fixed orface tube when there is a pressure differential to flow refrigerant. It flows with the engine off because there is still a pressure difference.

The VOV does change position due to pressure differential. IMO yours is working. The idle condition is where it makes the changes in position to improve cold air delivery.
 
I usually only run the blower on med-high (mark just before high on the switch) when I had changed it and checked pressures it was on high. I need to time the clutch cycling, I've had thoughts of rigging a small LED light in the cab just to see when it's on and off while driving. most of the time you can feel it cycle off and on while on the road. if I had to guess, maybe 2-3 minutes bewteen cycles with sitting still at 2500 rpm. on the road with more air to the condenser I would think it cycles faster. the cooler the temp outside like in the mornings it cycles frequently and doesn't seem to cool very well then.

I am wondering if the 105+ vov is a bit extreme for it here where it also doesn't perform very well cooling in the mornings when it's only in the 80's outside. I guess describing it, it's like once it opens up it allows too much flow like too large of an orifice and seems to stay that way.
 
I may have exaggerated on the time it cycles. it was about 75 degrees out this morning when I left for work, turned on the ac and it wouldn't cool at all till I turned into the plant, about a 6 mile drive at 60 mph speeds. I could feel the compressor cycle on for about a split second then off again for under a minuet or so constantly. when I turned into my work where it's about a 1/2 mile drive at 10 mph to the back parking lot from the entrance, that's when it started cooling it's arse off and my little dash thermometer went from 75 down to 40 degrees! started fogging up the windows as I got to the parking lot!
 
If it hasn't spring a massive leak... Or the lack of a high pressure cut-out hasn't vented some of the system charge...

Replace the low side switch. They are very unreliable aside of leaking that they also do often.
 
WarWagon said:
If it hasn't spring a massive leak... Or the lack of a high pressure cut-out hasn't vented some of the system charge...

Replace the low side switch. They are very unreliable aside of leaking that they also do often.
Click to expand...
I think I have another cycle switch. not sure if it's leaking. I wish I could adapt this thing to be able to use a better switch but the port threads are metric. if a dryer from an older truck (R12) would fit the line fittings maybe that would be a possibility.


jrsavoie said:
How is your fan clutch?
Click to expand...
fan clutch is awesome! it's the GM electro-viscous one with a duramax fan blade. when it turns on, it's like a wind tunnel under the hood. although it never turned on this morning I'm assuming the high pressure never got up enough to do that.
 
As I said above, the low pressure switch on the dryer is easy to replace and it is relatively cheap.
No need to evacuate the system to replace.

I had to replace a couple of those over the years and it always fixed that erratic cycling issue in mine.
Yours may be different, I am just relaying my experience.
I am in TX too, it may be a couple of degrees cooler in North TX but we have same AC challenge.

If it does not fix it, then it is cheap parts.
That means some other parts are bad like the compressor.
 
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