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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / August 2007Need Help - AC problem with a 2000 Honda CRV AC
We are having AC problems with a 2000 Honda CRV. We just did a successful vacuum and leak test, then recharged the system with 134a. At a constant 3000 RPMs, and with a set of AC gages attached to the low & high ports, the AC system does this: 1. The low pressure gauge rises in pressure until the high limit (low side) switch disengages the AC clutch. The high pressure gauge is within limits at this time. 2. When the low pressure gage returns to safe pressure, the AC clutch engages. This time the high side pressure gage begins to climb until it reaches the high side limit in PSI, and the AC clutch disengages. The high side pressure declines to a safe PSI and the AC clutch again engages. Now go back to #1 above and start the low pressure side rising to the upper limit. It is a continuous loop. The above is an endless loop of reaching max low PSI, shut off, reaching max high PSI, shut off, reaching max low PSI, shut off ... Even at a steady 3000 RPM, the above constant cycling does not do a satisfactory job of cooling the car. What's the problem? THANKS, Gene > We are having AC problems with a 2000 Honda CRV. > [quoted text clipped - 25 lines] > THANKS, > Gene Please give the following in actual numbers: 1) your interpretation of low side unsafe pressure 2) high side cut-off limit 3) high side safe turn-on point Also, what exactly is a "high limit (low side)" switch? I'm thinking you don't know how this system operates. I'll be glad to help if you fill in the above data. Toyota MDT in MO >> We are having AC problems with a 2000 Honda CRV. >> [quoted text clipped - 30 lines] > > 1) your interpretation of low side unsafe pressure I think it shut off at ~ 110PSI or a little less > 2) high side cut-off limit It was near 400PSI when it shuts off > 3) high side safe turn-on point Can't remember,but it was > 150PSI > Also, what exactly is a "high limit (low side)" switch? When the low side gets near the 110PSI area, it shuts off. > I'm thinking you don't know how this system operates. I'll be glad to > help if you fill in the above data. LOL - I definitelly do not understand this one. I would expect it to run at ~ 30-50 PSI on the low side and about 150 to 200 PSI on the high side, but not sure ? Thanks, Gene > Toyota MDT in MO > >> We are having AC problems with a 2000 Honda CRV. > [quoted text clipped - 54 lines] > Thanks, > Gene I said that not to be rude, but because you suspected high low side pressures as a cause for the system to shut down. This system (from the factory, atleast) has only one pressure switch that can control the compressor's engagement. It is a dual pressure type switch located on the high pressure line (the smaller diameter line) near the front of the vehicle, located in or near the receiver drier but I don't remember for sure. This switch will shut down the compressor at about 450 psi and also if the pressure drops below about 30 psi. There will be a "hysteresis range" of pressure around those points with this type of switch; this will cause it to stay off for a while after it passes back into the acceptable range of operation. Perhaps this hysteretic action is what you were describing. The bad news is that your symptoms do not lead to one conclusion. It doesn't sound like the dual pressure switch is causing the cutoff every time, and the gauges' behaviors don't lead me to a solid conclusion. I think I would have to see it for myself, or assume there is a moving piece of blockage in the high side, either in the condenser or the drier. Perhaps you have too much oil in the system too. If both gauges went high at the same time, climbing gradually, I would say it is probably overcharged. How much R134a by weight did you install? Did you reference the refrigerant charge sticker underhood? To what indicated vacuum and for how long did you evacuate? If the high side all-of-a-sudden pegged hard and the low side rose quickly afterwards I would suspect high side blockage. Condensers are the most common area for this manner of restriction. Another though is an inaccurate gauge set or the valves were open or leaking internally (along with an A/C problem). Toyota MDT in MO Thanks. I agree with your best guess, that it could be some blockage on the high side. The car was recently purchased used by my kids, so we have no historical AC data. I did three similar AC compressor replacements with these same gauges in the last month and all went 100% successfully - so I am pretty sure the gauges are OK. I pulled ~ 25-26 vacuum for ~ an hour with both low & high sides open. That should have been enough to get the moisture. Because I am doing it myself, here is the approach that I like, and will probably do in this case, assuming the problem persists. 1. Go to a local salvage yard & find the best AC compressor from a "wrecked" car. It must come from a reputable yard & have an unconditional 100% return for 90 days. To test it, I pour in an ounce of the appropriate oil into the compressor, turn it over by hand to check compression a few times, then pour out the oil onto a clean napkin. It must have good compression & no foreign matter in the oil. Next I test the clutch with a 12VDC+ to the clutch pin. Finally, I spin the pulley and use a stethoscope to listen to the bearing free wheel. If all of the above are OK, I install said AC compressor. Here is my logic for the above: a. Factory AC compressor are WAY too expensive. b. The lower priced new compressors are made in China. c. The rebuilt compressors are the patched trash that were returned. d. The used ones per above are the only ones that are in good condition & low priced. So far, I have never had a bad one. Just check them out first. 2. Buy all new O rings, seals, dryer, filter, etc. - I even replace the low/high port valves. 3. Remove the old compressor, etc. & flush the system 4. Install the used compressor with oil, etc. , do a complete vacuum & leak test - then fill with 134a. The TOTAL out-of-pocket cost runs from $100 to $250, depending on the car. In that it is so inexpensive to just do it right, this is probably what is best for this Honda. It's really not worth the time and effort to trace down a potential clogged point in the system for $200 or so. However, I really would like to know what the problem is with this Honda, I'm just currious:-) THANKS, Gene >> >> We are having AC problems with a 2000 Honda CRV. >> [quoted text clipped - 91 lines] > > Toyota MDT in MO > Thanks. > [quoted text clipped - 7 lines] > last month and all went 100% successfully - so I am pretty sure the gauges > are OK. Sounds logical, if other properly operating systems gave you acceptable low and high side pressures on your gauge set. > I pulled ~ 25-26 vacuum for ~ an hour with both low & high sides open. > That should have been enough to get the moisture. You should be seeing about 28"-30" on a low side gauge when under full vacuum. In actuality, about 29" is all you can pull depending on elevation, but an indicated 25"-26" worries me that maybe the vac pump isn't working properly. > Because I am doing it myself, here is the approach that I like, and will > probably [quoted text clipped - 29 lines] > test - then > fill with 134a. Sounds like a good method to obtain a good, working compressor, but.... what makes you think that a compressor and drier replacement is going to fix this CR-V? What's wrong with the current compressor that you can prove with testing? > The TOTAL out-of-pocket cost runs from $100 to $250, depending on the car. > [quoted text clipped - 3 lines] > point in the system > for $200 or so. If you can get the system to run long enough, you can test temperatures along the high pressure lines, drier, and condenser tubing to locate an unusually cold spot. That would be where the restriction is (unless you are dealing with a massive overcharge... I still haven't seen an answer to my charge quantity/method question). Toyota MDT in MO Thanks. Good idea ~ testing for a cold spot. The AC is working, just cycling on and off - cooling is marginal at best. Can't hurt anything to just run it for a while. I placed 2 full cans in it - which was enough to make it cool. I was afraid to stuff any more into it, given the 400PSI readings. The easiest way to resolve the problem is to just replace everything per my earlier post. I think I can do it for ~ $200 total. Other than my just being curious, it's not worth spending the time to find a clogged area. A blocked area is caused by something broken in the system - usually the compressor. So just replacing everything for $200 is the only real solution as I see it. I was hoping that there was a common problem with this specific condenser in this model Honda. Thanks, Gene >> Thanks. >> [quoted text clipped - 85 lines] > > Toyota MDT in MO > The AC is working, just cycling on and off - cooling is > marginal at best. Can't hurt anything to just run it for a while. 450 psi spikes can't hurt? Mmmmkay... > I placed 2 full cans in it - which was enough to make it cool. > I was afraid to stuff any more into it, given the 400PSI readings. 24 oz is approximately the correct charge but I don't have the spec handy. If the cans of R134a had other crap in them you may have just boned the system. Either way, 24 oz of pure refrigerant wouldn't cause this odd pressure behavior. > The easiest way to resolve the problem is to just replace > everything per my earlier post. I think I can do it for > ~ $200 total. Other than my just being curious, it's not > worth spending the time to find a clogged area. A blocked > area is caused by something broken in the system - usually > the compressor. Usually not. > I was hoping that there was a common > problem with this specific condenser in this model Honda. It's a reality with most modern high efficiency condensers. I don't know if that particular part is more failure prone than others. Toyota MDT in MO |
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