Automotive Air Conditioning Information Forum (Archives)

TheApocalyptican on Sat June 15, 2013 4:03 PM

Year: 90
Make: Chevy
Model: Suburban
Engine Size: 5.7
Refrigerant Type: 134a
Ambient Temp: 95
Country of Origin: United States

I don't have actual pressures right now, but I know that this problem existed when it was r12 as well. Basically, I get great cooling when driving, but when stopped temps will go up to 60°F+. This gets the air feeling a bit muggy, and obviously not as cool as driving, which can be as low as 40°F. You'd be hard pressed to find someone who has better cooling of the condenser. I've got a fan shroud on the radiator, I've got the radiator sealed to the condenser, and the condenser sealed to the core support. So basically, air HAS to go thru the condenser. I've also got pusher fans on the condenser. The condenser is a true PF. I don't know what else could be done for idle temps. Now, my main comparison is to my Dad's 2006 Express. It drives, and idles around 40°F at the vents. I know that it was made to run r134a, and mine wasn't but mine did this on r12 too. I've compared the condensers, and the Express' is a bit bigger, but the Suburbans is thicker. So with all of this added up, they are about the same size. His rad, and condenser, and core are NOT sealed together like mine are. So, to me, this leaves the evap, and the compressor. I would think that the evap, could effect the temps, but not as much as the compressor could. So to me, this says that it's the compressor that's the issue. The Express has a 10S17F that is the original from the factory that has about 200,000 miles on it now. The Suburban has an R4 that is a new NOT rebuilt compressor. Would switching to a newer more efficient compressor be the key, or am I overlooking something else?

iceman2555 on Sat June 15, 2013 10:47 PM

First, is the system properly charged? How as the system charged and how much refrigerant was introduced into the system?
Secondly, check the engine cooling system, esp the fan clutch. It does not appear that the replacement of the compressor is the answer to your concern.
Let us know more....prior to spending the cash and time for a replacement unit.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

TheApocalyptican on Sun June 16, 2013 2:24 AM

Cooling system is great. Almost new fan clutch moves a ton of air. Moves a decent amount even when not fully engaged. System has the aftermarket PF condenser, so the stock 3.25lbs of r12 has to be reduced beyond the typical r134a conversion amount. After just recently being able to use a friends charge and recovery system, I've basically tried all up and down around where the charge should be, to no real avail. Can get the pressures in range but never can get enough cooling. I've also had in the past a reputable shop charge it with no real success. They also charged it with r12 prior to the pf install, and it also had the same problem of cooling at idle. System has always been charged after a good long vacuum, and has been done by machine, and by individual cans, and even the cans I did by weight as best could be done. Also, the heater core has valves setup so that it can be bypassed for anytime but winter.

Edited: Sun June 16, 2013 at 2:28 AM by TheApocalyptican

NickD on Sun June 16, 2013 5:40 AM

If this is a big black SUV like other big black SUV's even the shop manual with this crumby CCOT system and the R-V compressor states that at 95*F, low side pressures can be as high as 65 psi!

You don't get any cooling at 65 psi, be darn lucky to get vents temperatures down to around 75*F! What helps a tad, and just a tad is if you also have a rear evaporator/blower addition, but that R-4 can barely keep up with it. What I am trying to say, these systems weren't even worth a darn when brand new out of the factory. Unlike the good old POA systems that held that low side pressure to a constant 28.5 psi in conjunction with a TXV valve.

Bet it cools better at 3:00 AM in the morning. Least you don't have the hot sun beating down. Is bearable with just a front passenger riding or alone having the blower at max blowing 75*F air at your face, can be terrible if the vehicle is loaded with hot sweaty people.. Reducing the charge doesn't help too much either to reduce that low side pressure, then you are pumping foam. Besides that, at lower temperatures the R-4 will cycle like crazy.

Whether converting to a V-7 is a good question, Bohica would know since he lives in Vegas.

MrBillPro on Sun June 16, 2013 10:46 AM

I have a 99 Suburban, looks like I just drove it off the new car lot, I have had to change out the Compressor on it once. I also changed out the rear txv because a lot of metal/trash got into the system and clogged the screen, was really not to hard of a job. My Suburban will run you out after about 20 miles down the road, these things are like cooling a small home, you can't expect to drive them up to the corner store and it be 70° in the car, on a 95° day. What I do is if no one is riding in the rear seats, is turn the rear air off and the front on high, it really helps the front cool a lot faster. GM should have installed a rooftop unit like on a travel trailer on these big dogs. If I am just running the front air, the suction will be around 35/36 and the vent temps will be around 42° at idle, I find it always "in my suburban" even with passengers to initially run the front air first, and then switch on the rear. I don't know what kind of blower motor they have in the front, but that thing on high will almost blow the windows out, I need to put one of those blowers in my GMC service truck, it don't blow near as good as the suburban.

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Don't take life seriously... Its not permanent.

TheApocalyptican on Sun June 16, 2013 2:12 PM

Truck is tan. Only way I'd own a black car here in Vegas is if I knew that the A/C had meatlocker ability. I've also built a partition the goes up a little behind the 2nd row seats. So almost the entire cargo area(3rd row has long been removed) is cutoff, and doesn't need to be cooled off. Also, I don't have rear system anymore. So basically, I've got more of a crew cab, than a Suburban. Oh, and one last thing, in case anyone here didn't know, even though it's 90, the SUVs didn't change body style until 92. So my truck and it's system is like the pre 88 pickups.

NickD on Sun June 16, 2013 4:38 PM

GM made great improvements in both ride and AC in the 96 models, something to look into.

iceman2555 on Sun June 16, 2013 5:47 PM

Quote
TextSystem has the aftermarket PF condenser, so the stock 3.25lbs of r12 has to be reduced beyond the typical r134a conversion amount. [/Q

Not sure what the typical recharge amount for a 134a conversion is, but if the statement is correct, your system is undercharged drastically. If the condenser was replaced with an updated unit, there is no need to reduce the recharge amount. The extra cooling efficiency of the condenser will handle the pressure demands of 134a. Recharge the system to the OE spec's.
The procedure of 'undercharging' a retro fit was to assist with the high side pressures associated with 134a. This amount of undercharged was not a set amount, just a assumed volume and the standard procedure was to charge to a specific pressure. The only problem, there are no specific pressures for a retro fitted system.
Good luck!

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

NickD on Mon June 17, 2013 6:15 AM

Basics are still the same, regardless of refrigerant, orifice must be supplied with solid liquid, foam never cools very well. Good old fashion sight glass helps to achieve this goal.

With R-134a, high side pressures will always be higher, and low side pressures lower than R-12, so the cycling switch must be readjusted to compensate for this very basic fact.

Key pressure to watch is the high side with R-134a in an attempt to gain solid liquid, don't want to have a system that is ready to blow its cork. This is where a larger condenser comes into play with sufficient cooling, in particular at higher ambient temperatures.

Also with R-134a, have to use a lot more care to keep any moisture out of the system or acids will form, plus compatibility issues. R-4 may not be the best choice for R-134a, a large tin can with two large O-rings for seals, plus puts an extra load on the belt drivetrain with that large diameter configuration augmented by higher pressures.

Even after all this, may learn the system is just under designed for a vehicle of this type. Certainly took GM long enough to realize this, finally completely a major redesign years after.

apexair on Mon June 17, 2013 6:40 AM

You have to keep in mind that an A/C compressor can easily rob about 5 hp from your engine. When you're gunning the thing balls to the wall in neutral, that's not an issue; when you're trying to accelerate up a hill, it is. The compressor clutch will disengage for several seconds or more while the drive train needs that power. I suspect this is what's happening in your case.

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Apexair provides you with a variety of home air conditioners with stylish, sophisticated design

GM Tech on Mon June 17, 2013 7:23 AM

Trucks did not use WOT (wide open throttle) cut-outs- especially older ones...at least until the early 2000 models or so...cars did/do.......

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

MrBillPro on Mon June 17, 2013 9:05 AM

I know my suburban has a txv in the rear, in my a/c business "Commercial and Residential" when you change refrigerants you have to change the metering device, don't know if you changed yours or not, but 134a will never work with a R-12 metering device. Again, it's 94° in Houston with probably 75% humidity, cooling off one of the big boxes is hard. My suburbans system is tweaked to the max, cools great, but remember all that heat in the big box of a vehicle, is relying on a small evaporator coil, what maybe 1' x 1' to pickup up all that heat, and send it up front to be dissipated? If the evaporator was as big as the condenser, it would cool down lots faster.

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Don't take life seriously... Its not permanent.

iceman2555 on Mon June 17, 2013 11:13 AM

In order to properly diagnosis a system performance issue, it is essential that the system be charged properly. The poster clearly states in his post that the system was undercharged lower that the typical 134a conversion. What is a typical 134a undercharge? Since no one published specific retro fit recharge amounts, then how much refrigerant is in the system?
The major deficiency between 134a and 12 was the high side operational pressures. Low side can be a bit lower and the adjustment of the LPCO to accommodate this was never proven with a valid controlled test. If my memory serves me correctly, the gentleman that proposed this procedure actually 'backed off' this assertion after experimenting with various vehicles over a period of testing at SIU. The change of the condenser should be sufficient to accommodate the increase pressures associated with 134a and such should allow for a complete system recharge. Over the retro fit period, each time we made changes to the condensing units we were able to increase the charge rate back to OE spec's.
The gas utilized in most known TXV's today is 134a. It is not known any TXV mfg'ers that produce a specific R12 valve today. There are some off shore units that utilize various other gases and these have presented some serious cooling performance concerns for the after market.
The first concern for this performance issue and the statement that the system cools under these conditions and does not under these conditions and the statement that the engine cooling system is up to par, combined with the statement stating the amount of system charge as being below a set standard, tends to reinforce the concept that the system does indeed have an insufficient amount of refrigerant. One could suppose that the system was charged to a specific perceived acceptable pressure and allowed to operate under this assumption. A major concern would be that there is not an 'acceptable' pressure for a retro fitted system. Most tend to accommodate an 'adjusted' R12 type pressure but this does reflect the temp/pressure change of between 12 and 134a. Often the removal of refrigerant or a 'balance' of charge rate to accommodate or rectify an excessive pressure was the norm for many. However, this is not a valid method to insure proper cooling efficiency or system charge rates.
This system should be charged with a specific amount of refrigerant, allow for basic thermal diagnostics and determine the performance issue. It is doubtful that the compressor is the issue.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

TheApocalyptican on Mon June 17, 2013 6:14 PM

As I said above, I was able to use an actual charge and recovery machine recently. And after doing so, I have tried basically everything from a 52%(27oz) of r12 charge, up to 100%(52oz). What gave the best cooling was 75%(39oz). At 100%, the clutch would freak out and do a rapid on/off cycle when first kicked on, then wait a bit, and do that same rapid cycle, and sometimes it would do it one more time, and then the system would actually stay on, but the temps were high, and so was the high side pressures.
The orifice tube is right before entry to the evap box, and it leaves almost no tube after the orifice that can be accessed, but along with the best temps, at 75% the in/out of the evap is within 5° of each other. From everything I, and the local shop have done, the system should work perfectly. But it doesn't when idling. Works fine at speed. I expect some drop off at idle but a 20°F+ difference when only at a light for a short time can't be right.
Also, as said before, this problem existed with r12(at 52oz) as well, albeit, with the stock condenser, but did have pusher fans in place.

iceman2555 on Mon June 17, 2013 10:50 PM

Is this a dual zone AC system? It is difficult to understand that the evap would flood with a 21% undercharge. What were the test conditions of the vehicle/AC controls when this 5 degree variance was tested and how as it tested.
You may try testing with a high heat load...max air...high blower...both front doors open...engine at idle. Post evap temps and also condenser inlet and outlet temps.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

TheApocalyptican on Tue June 18, 2013 4:06 AM

Front A/C only. I always test on high blower. 5 degree was most temp ranges, and in park, generally at 1000 to 1500 rpm. The ~75% charge was what I used for a while, as it seemed to be the best temps. Then when I was able to use the recovery machine, it confirmed the 75% charge was best. At that time, I used 1500, and 2000 rpm. 2000 was slightly closer in temp than 1500, but as soon as vehicle was let to return to 750, the temps start to go up, and the evap inlet outlet difference increases. I generally have the drivers door open, and the passenger window open when testing when parked.
I'll try the test you suggest and post back. I appreciate all the help iceman. This problem has been driving me nuts for a while, and any confirmation of the cause would be a great help.

iceman2555 on Tue June 18, 2013 6:05 PM

Perform one other test. Follow the discharge hose from the compressor to the condenser. Is the attachment at the top or bottom. Also, most of the condensers for this model vehicle have the orifice tube located in the condenser outlet. Is there any chance this condenser has a orifice tube there also. Just checking for possible issues. Trying to remember when GM started the same size condenser inlet and outlets. This allowed for a condenser to be mounted upside down or plumber backward.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

TheApocalyptican on Wed June 19, 2013 3:38 AM

I'll have to look at the lines. Definitely no orifice in the condenser. Only one is right before evap. Almost positive the condenser fittings are different sizes, but doesn't mean that the lines on the condenser itself aren't backwards though. The aftermarket condenser I have that is a direct fit, is basically a regular aftermarket universal condenser like is sold on this site with lines welded on that snake to the correct spot and some brackets welded on as well.

NickD on Wed June 19, 2013 6:46 AM

Posting pressures would sure help rather than by guessing at what percentages should be used, besides that, the system was already changed making the provided capacities worthless.

Engine at 1,500 rpm, doors open, blower at max, AC on, and specify both ambient temperature and RH.

TheApocalyptican on Thu June 20, 2013 4:21 PM

Ok. IR thermometer died, so no evap temps. Compressor is attached to the top of the condenser, the orifice tube line to the bottom.

Pressures:
95°F ambient from thermometer , 5% RH according to weather service.
at 1500 28 low, and 220 high.
at 750(idle) 60 low and 160 high.
This is what it always does. Higher rpm equals good numbers, idle gives me high low side, and low high side.

Also , I now(again) have an electric cooling fan for the rad as well as the condenser ones. And, I verified that it isn't airflow thats the problem, as putting it into neutral on a big hill, where it can get plenty of air movement, the temps still rise due to the compressor being at lower rpm.

Edited: Thu June 20, 2013 at 4:24 PM by TheApocalyptican

NickD on Fri June 21, 2013 6:02 AM

With that R-4 in a CCOT system at the higher speed, would expect to more in the 45-50 psi range at the low side, you are low on charge. With a sight gauge, would be seeing a lot of foam. At idle, will see that low side pressure go down.

Would slowly add refrigerant, only have one vent open with a thermometer struck in there at 1,500 rpm, see if that temperature goes down while slowly adding charge. If adding a tad more refrigerant does not lower the vent temperature, you are just about there, best you can do with these systems.

Other signs, but not sure at that low RH, may see a frost line on the accumulator, should be half way high. Yet another sign, would be comparing the evaporator outlet temperature with the inlet, outlet should approach the inlet. High side will jump to around 275, have to live with that. Adding an external fan may help or hinder.

It's not the best system in the world, having a POA valve with a TXV was great back then, but made these systems a lot cheaper.

TheApocalyptican on Fri June 21, 2013 4:58 PM

Put more in little by little. All it did was slowly raise both pressures. At 750, the low side and high side went up. At 1500, the low side and high side went up. The 1500 range is around 45, but now the 750 low is at 70.

NickD on Sat June 22, 2013 8:11 AM

Working backwards, assume you have an R-134a compatible accumulator, what about the evaporator, ever clean that up? Usually find a ton of debris on the face of it.

TheApocalyptican on Sun June 23, 2013 3:40 AM

The Evap was replaced by the previous owner, so it's not that old, but it's the other part of the system that I was questioning, but wasn't sure how big a difference it could make. As far as it being clean, I checked it. I didn't clean it because it looks almost brand new. I can see one side by removing a duct connector, and I can see the other side thru the blower motor hole. Had to use a small mirror to see 100% of it, but it's nice and clean. Accumulator is r134a compatible. Actually been thru a couple of the them since I first got the truck, and have been trying to get the a/c to work correctly.

NickD on Sun June 23, 2013 5:57 AM

Maybe someone else can step in with suggestions. I am lost, typically in an R-134a retro, at idle, the low side pressure is so low, have to decrease the size of the orifice from a 72 mil down to a 68 mil to reduce cycling.