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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / July 2006R134A help needed; 1998 Suburban.
I have a 1998 Suburban with the 5.7L V8 engine. My wife has observed that the AC in this SUV is not quite as good as my 1995 Blazer AC with a 4.3L V6 engine (it does very well). I bought the Suburban used, and had a mechanic check/charge the system right after I acquired it (EBAY purchase). From what I can tell, the system is working just as good as the day the mechanic serviced the system 4 years ago. But I have to agree with my wife that it could be better. I have guages, and have measured the high and low sides (while the AC was running on high/max) as follows: High Side: About 135 PSI (might be flucuating slightly, but not sure). Low Side: Flucuating between 52 and 54 PSI; mostly stays at 54 PSI. Outside Temperature at time of measurements was 100 degrees F. Air was blowing cool/cold, but not freezing cold. I don't know what the pressures should be for this system; I'm hoping somebody could help me evaluate the system before I take it to somebody for servicing/repair; that way I might be able to tell if they know what they are doing, or if they are tyring to rip me off. Thanks for any help, and Best Regards, John Hermann > ... > High Side: About 135 PSI (might be flucuating slightly, but not sure). > Low Side: Flucuating between 52 and 54 PSI; mostly stays at 54 PSI. > ... I'm not an A/C expert but the high side seems a bit low. Go to http://acsource.net/acforum/ and ask. The guys there are very knowledgable & helpful. Thanks for the responses. I too was thinking that the high side pressure was kind of low. A couple of more things to note... 1) The gauges I'm using are a cheapo Harbor Freight set; just picked up a set for taking these measurements; so either value could be off if these gauges are known to be problematic. 2) The pressures were measured at idle (I assume around 800 RPM). 3) If the pressures are valid, then from what I read, the low side may be too high; too much charge? I was not able to measure the temp coming out of the vents; but if I were to guess, I'd say around 50 degrees. Best Regards, John Hermann John Hermann wrote: > ... > High Side: About 135 PSI (might be flucuating slightly, but not sure). > Low Side: Flucuating between 52 and 54 PSI; mostly stays at 54 PSI. > ... I'm not an A/C expert but the high side seems a bit low. Go to http://acsource.net/acforum/ and ask. The guys there are very knowledgable & helpful. John Hermann Wrote: > Thanks for the responses. I too was thinking that the high side > pressure was kind of low. A couple of more things to note... [quoted text clipped - 27 lines] > Go to http://acsource.net/acforum/ and ask. The guys there are very > knowledgable & helpful. Your pressure reading shows a weak compressor or open expansion valve/orfice tube. If to much freon the high side would go high very quick. Does it have rear air? If just front air check or replace your orfice tube. If rear air it could be rear expansion valve or front orfice tube. If rubber hose to rear pinch it off and see if pressure starts working better. Low side should be around 30lbs and high will range around 150-250 lbs. MT  SignatureMT-2500 http://www.automotiveforums.com Yes, the Suburban does have rear air. Another thing I forgot to mention is the AC compressor was engaged the entire time I was testing; it never cycled off. Best Regards, John Hermann John Hermann Wrote: > Thanks for the responses. I too was thinking that the high side > pressure was kind of low. A couple of more things to note... [quoted text clipped - 27 lines] > Go to http://acsource.net/acforum/ and ask. The guys there are very > knowledgable & helpful. Your pressure reading shows a weak compressor or open expansion valve/orfice tube. If to much freon the high side would go high very quick. Does it have rear air? If just front air check or replace your orfice tube. If rear air it could be rear expansion valve or front orfice tube. If rubber hose to rear pinch it off and see if pressure starts working better. Low side should be around 30lbs and high will range around 150-250 lbs. MT SignatureMT-2500 http://www.automotiveforums.com -- John Hermann Buy, Sell, Trade, and Repair Video and Pinball Machines. Located near Dallas, TX. http://www.geocities.com/SiliconValley/Circuit/8393 I agree that it sounds like the compressor is weak. Is it making any noise which could indicate a failed TXV for the rear A/C and liquid slugging? Also check to make sure the A/C belt is not slipping or loose. Head pressure should be at least 50-60PSI higher. Most likely you need a new compressor. Replace the drier and/or accumulator as well and observe the pressures as you charge (after evac of course) with both the front and rear A/C on. If the rear TXV is gone and flooding the rear evap, your suction pressure won't come down properly and you may start hearing the compressor chugging liquid. If you do, stop and turn it off before damaging the new compressor and replace the rear TXV. These are known to be bad on Suburbans. The sensing bulb clip that attaches it to the evap return line does not work great and causes the TXV to open fully. dave mc With the engine running at 600-700 rpm the compressor is going to be weak.Take the readings with the engine running at 1500-2000 rpm. Air should be on recycle. Pumping 100 degree outside air at idle won't get you much temperature drop. >I agree that it sounds like the compressor is weak. Is it making any > noise which could indicate a failed TXV for the rear A/C and liquid [quoted text clipped - 12 lines] > > dave mc > With the engine running at 600-700 rpm the compressor is going to be > weak.Take the readings with the engine running at 1500-2000 rpm. Air should > be on recycle. Pumping 100 degree outside air at idle won't get you much > temperature drop. The readings should ideally be at 1500 RPM, so yes I agree that they should be re-taken. but sorry, even at 800 RPM they should be better than this. You will wait a long time to cool a Suburban at 100 deg F ambient with these pressures. Head pressure at 100 F ambient should be on the order of 220-250 PSI. davemc >I have a 1998 Suburban with the 5.7L V8 engine. My wife > has observed that the AC in this SUV is not quite as good [quoted text clipped - 22 lines] > > John Hermann To start off with, the pressures will vary considerably depending on a number of conditions. For instance: High side pressure varies with ambient temperature, humidity, air flow through the condenser, compressor speed, and restrictions in the system. Low side pressure varies with in cab temperature, air flow across the evaporator, humidity, heat load on the vehicle, compressor speed, restrictions in the system, Here is one scenario that you might use as a guide: Start the engine and turn on the A/C system. Place the controls on Max A/C and high fan. Run the engine at 1500 rpms for about 20 minutes with the vehicle out of direct sunlight and all the windows closed. Lets assume the ambient temperature is at 95F and the humidity is between 60% and 80%. Lets also assume the radiator cooling fan is functioning properly and the fan clutch is not slipping. The condenser and radiator fins are clean. No air dams or fan shrouds are missing. The engine is not overheating. We will also assume the A/C blower motor is functioning properly and none of the plenum blend doors are leaking or stuck. At this point the temperature inside the cab should have stabilized and the air temperature at the vents is as cold as it will get during the performance test. That should be somewhere in the neighbor hood of 45F with the fan on high and checking the temperature at the vent closest to the evaporator core. Even slight variations in ambient temperature humidity or air flow could affect the air temp as much as 10 degrees either way. While the engine is still running at 1500 rpms and the compressor clutch is engaged. The low side gage should read between 26 and 42 psi. and may cycle the compressor off occasionally. The high side should be between 225 and 275 psi. There again slight variations in conditions can affect the pressures quite a bit. If all these conditions are met then the system is probably performing up to specs. Keep in mind that any variation in the conditions will affect the pressure readings. Also consider that the Suburban has a much larger area to cool than the Blazer, and they both have basically the same capacity refrigeration system. Hope this helps. SignatureKevin Mouton Automotive Technology Instructor "If women don't find you handsome, they should at least find you handy" Red Green Kevin, with a head pressure of 135PSI, he definitely does not have a condensor or fan clutch issue, at least not as a primary problem. Condensor issues will show with too high a head pressure normally. dave mc > Kevin, with a head pressure of 135PSI, he definitely does not have a > condensor or fan clutch issue, at least not as a primary problem. > Condensor issues will show with too high a head pressure normally. > > dave mc I agree. I just mentioned some of the things that could cause readings to vary, one way or the other. >> Kevin, with a head pressure of 135PSI, he definitely does not have a >> condensor or fan clutch issue, at least not as a primary problem. He sure might have a weak compressor problem, however. On the other hand, that doesn't jive with it getting down to 50* vent temperature. Bottom line is the readings don't mean much without knowing ALL the parameters. Don www.donsautomotive.com >> Condensor issues will show with too high a head pressure normally. >> >> dave mc > >I agree. I just mentioned some of the things that could cause readings to >vary, one way or the other. Okay, here's the latest; again, I appreciate all of the help/info everybody is giving. First off, I don't know what I'm doing, so I took the car to a mechanic and he hooked up the gauges and got completely different values on the high side. At idle (800 RPM), the readings were: Low Side: 54 PSI High Side 290 PSI He revved up the engine a bit and the pressures changed; I didn't take notes, but he said things were looking reasonable. He basically confirmed everything that has been discussed in this thread about Suburbans being very large, and the AC's struggling to cool them in such hot weather. We measured the temps coming out of the vents to be 70 to 75 degress standing still, and dropping down to as low as 65 degrees when driving around. He noticed a bunch of dead bugs and debris in the condensor coils, so he just blew it out with compressed air; that got the temps to drop to as low as 55 degrees while were were drive around; outside temp was 100 to 101. The mechanic noticed some noise coming from the compressor, and suggested that some oil could be added to reduce it; also there was evidence that some of the oil is leaving the system because the compressor is a bit dirty/oily. I priced a new compressor, and Oreily's wants $448 dollars; so that's a major expense; I would not install a remanufactured compressor if a compressor is ever needed. The only thing I'm not sure about is the low side; from what I've read on the internet, 40 to 50 PSI is typical. The mechanic seemed to think that the low side was okay and suggested instead of removing some R134A, that the system should be evacuated, add the oil and a new orafice tube and recharge to the exact system spec (4 lbs 2 oz of R134a). Of course this would cost hundreds of dollars to do. Would lowering the low side by 5 or 10 PSI help with the inside air temp in this 100+ degree weather we're having? If so, what value should the low side be set at? Or is the low side already correct? How much life should I expect to get out of my old compressor (if I have the system serviced as suggested)? The noise he heard didn't seem bad to me; I thought it was normal. I'm reluctant to do the service as suggested because the mechanic could not guaranty that the performance of the system would improve; it would be a do it and see what you get thing; and the compressor could still die in a year and I'd have the major and very expensive repair also. Again, thanks to everybody helping out with this thread. Hopefully the info will help others too. Best Regards, John Hermann >> Kevin, with a head pressure of 135PSI, he definitely does not have a >> condensor or fan clutch issue, at least not as a primary problem. He sure might have a weak compressor problem, however. On the other hand, that doesn't jive with it getting down to 50* vent temperature. Bottom line is the readings don't mean much without knowing ALL the parameters. Don www.donsautomotive.com >> Condensor issues will show with too high a head pressure normally. >> >> dave mc > >I agree. I just mentioned some of the things that could cause readings to >vary, one way or the other. Ok so that high side reading is VERY different from what you stated initially. You can try spraying the condensor with water to see if you get better cooiling. If you do, then you would have to start looking at the condensor and fan/clutch. Evacuating and recharging it at least may be a good idea since you may be slightly overcharged with these new readings. So I think people have brought up some good points here with regards to the cabin size of the Suburban and the fact that you have rear air as well. The suction pressure of 40 PSI sounds high to me and will affect the vent temps, although I don't have a lot of experience with systems using rear air. I still think you should be getting better vent temps and it will probably take $$$ to fix it. The fact that your compressor is noisy is most likely an indication that it is weak or damaged. It may have been damaged by your rear air TXV flooding and returning liquid to it. This is why I'm saying to look at that rear TXV as a potential trouble maker. good luck dave mc >Okay, here's the latest; again, I appreciate all of the help/info >everybody is giving. First off, I don't know what I'm doing, so [quoted text clipped - 17 lines] >to as low as 55 degrees while were were drive around; outside temp >was 100 to 101. Sad to say, you probably won't get it a whole lot better -- maybe a little.. > The mechanic noticed some noise coming from >the compressor, and suggested that some oil could be added to >reduce it; Unfortunately, this is frequently done with no knowledge as to what the oil level really is. Excess oil does not help a compressor and, in fact, makes it work a lotharde as it is not compressible. Excess oil will reduce cooling. > also there was evidence that some of the oil is >leaving the system because the compressor is a bit dirty/oily. [quoted text clipped - 8 lines] >orafice tube and recharge to the exact system spec (4 lbs 2 oz of R134a). >Of course this would cost hundreds of dollars to do. It should be only a couple hundred or so. >Would lowering the low side by 5 or 10 PSI help with the inside air >temp in this 100+ degree weather we're having? If so, what value >should the low side be set at? Or is the low side already correct? That depends on how long the system was running and if the rear AC was turned on. The longer it runs and cools down inside the vehicle the lower the low side pressure will be. Its best to evaluate with the rear AC turned off so that it bewhaves like a front only system. The rear has an expansion valve which close with no airflow through the evaporator. >How much life should I expect to get out of my old compressor They don't hold up well at all in these vehicles. Don www.donsautomotive.com >(if I have the system serviced as suggested)? The noise he heard >didn't seem bad to me; I thought it was normal. I'm reluctant [quoted text clipped - 27 lines] >>I agree. I just mentioned some of the things that could cause readings to >>vary, one way or the other. >>I have a 1998 Suburban with the 5.7L V8 engine. My wife >> has observed that the AC in this SUV is not quite as good >> as my 1995 Blazer AC with a 4.3L V6 engine (it does very >> well). To be expected -- see below. >> I bought the Suburban used, and had a mechanic >> check/charge the system right after I acquired it (EBAY [quoted text clipped - 34 lines] >Start the engine and turn on the A/C system. Place the controls on Max A/C >and high fan. Run the engine at 1500 rpms Good point, of course. To my knowledge there are NO shop manuals for any make of vehicle that specify AC pressures at idle > for about 20 minutes with the >vehicle out of direct sunlight and all the windows closed. [quoted text clipped - 11 lines] >air temperature at the vents is as cold as it will get during the >performance test. That should be somewhere in the neighbor hood of 45F Going down the road the vent temperatures are typically 5-8*F cooler under severe heat loads than at a stop. > with the fan on high and checking the temperature at the vent closest to the >evaporator core. Even slight variations in ambient temperature humidity or [quoted text clipped - 12 lines] >Also consider that the Suburban has a much larger area to cool than the >Blazer, Suburbans have always been known for taking quite a while to cool down inside. Here in Texas you see a very high percentage of them with aftermarket window tint -- the blackest the law allows -- that was applied in a desperate attempt to help out a struggling AC system. > and they both have basically the same capacity refrigeration system. And if you have a dual system and turn on the rear air the pressures will be higher -- both suction and discharge-- and the front vent temperatures will be higher. Don www.donsautomotive.com >Hope this helps. |
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