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Faulty Expansion Valve?

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  • #16
    I'll be waiting to hear the results. Tx's never fully close or open, they should always pass some and there should be some restriction as well, not a plug or a straight thru either.

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    • #17
      I couldn't tell that this one was allowing any air through.

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      • #18
        The new Tx valve arrived yesterday and I noticed immediately that it's possible to blow through the new one while the old one is more-or-less blocked as I mentioned in an earlier post, so hopefully that's the problem. I installed the valve and vacuumed down the system. I'll check tomorrow for holding of vacuum and then charge again. I'll report back.
        One other question. When reading the gauges, what RPM and other conditions should I ensure? Fan on high, pusher fan on (aftermarket), etc.?
        Thanks very much and wish me luck.

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        • #19
          Seem you got it and yes I WISH YOU LUCK!
          Tom
          MetroWest, Boston

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          • #20
            I charged the system with 2.25 lbs. of r134a and got the following gauge readings at 85° ambient taken right in front of the condenser. This reading was taken at idle without the pusher fan that was added. 240's have a mechanical fan that runs constantly.

            Click image for larger version

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            Turning on the pusher fan netted this result:

            Click image for larger version

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            From looking at a temp/pressure chart, it appears that the gauge numbers don't jive with the pressure readings I'm getting. I drove the car on the freeway and was getting about 42° at the center vents when it was around 80° outside. It seems to be working well, but I'm just not certain on charge amount.

            With that being said, I don't think I've ever seen any old Volvo, even my '93's that came with r134a, deliver over about 35 lbs. even with a fresh weighed charge on the low side. Those cars don't have a high-side fitting, so it's impossible to tell what pressure they are running. With this '90 model and the Franken AC setup, who knows?

            Should I go by pressures with the auxiliary fan on or off?

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            • #21
              Ok, what does the system call for when charged with R12? Are you putting the same amount in by weight of 134a? you should put between 75%-80% by weight when 134a is used to replace R12.
              Both the reduced pressure when the acc fans are activated and the pressures vs. temp make me think it might be slightly over charged.

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              • #22
                I was going by the Volvo service bulletin (Greenbook) for converting over to r134a, which states to use 2.2 lbs (35.2 ounces). The system uses 41.5 ounces of R12 originally, so the recommended charge of r134a is 85% or the R12 charge.

                If it were slightly overcharged and some refrigerant were removed, wouldn't that decrease the low side further? From the chart, it appears that the low side is already slightly low.

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                • #23
                  I HATE charts, I think they mislead more people. Look at the numbers in the blue and red bands, they show the temp of the refrigerant at the point measured. They show 36 deg F for the low (evaporator) temp and 128 F for condensing temp. No reason the low side can't be lowered to around 32 deg and the high side will come down a bit too if better cooling, your over 40 deg above ambient for condensing temp, that isn't good.
                  I'd pull a little refrigerant back out and see where the pressure/temps are at.
                  As long as the compressor is staying on (the frost switch is not what is holding the low side at 36 deg) then I would say both low and high side are a little high for the ambient temps you are reporting.

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                  • #24
                    What RPM should I be checking the pressures at?

                    Also, should I check with the added pusher fan running or with it off?

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                    • #25
                      I'd check at 1000-1500 with the acc fan on, Best way to simulate road conditions.

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                      • #26
                        Another thing you can try is to "mist" the condenser with water while watching the high and low side, if the pressures both drop and the low side levels out around 32 deg, I'd say you either have a degraded condenser or your not getting enough air across it.
                        I"ve not seen a car since the 70's with a rigidly driven fan, most have a viscus coupling that drives the fan all the time but not at the pulley speed until it senses enough heat, and supposed to "lock on" and drive faster. If you have a viscus coupling and not a solid drive, I would suspect the coupling.

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                        • #27
                          I'll recheck and report back. BTW, this is a new parallel-flow condenser that I installed recently.
                          These cars do use a viscous coupling. I should say that there's plenty of room for air to go around the condenser in these cars. The fitup is hardly a tight one and that may be affecting its efficiency.

                          So just to confirm, I should be shooting for 32° low side and less than 40° above ambient for the condensating temperature, correct?

                          Thanks for all the help!

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                          • #28
                            A quick check on Rockauto shows the '90 240 uses a viscus fan clutch. I would change that if it is more than 5 years old.

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                            • #29
                              Originally posted by Wren View Post
                              I
                              So just to confirm, I should be shooting for 32° low side and less than 40° above ambient for the condensating temperature, correct?

                              Thanks for all the help!
                              yes, that is what I'd shoot for, Also if you are not getting air thru the condenser that can also effect the performance a lot. You can try adding some rubber "dams" around the condenser to seal it to the radiator to increase the air flow thru the condenser.

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                              • #30
                                I reckon that's why I'm getting better numbers with the pusher fan running. The numbers shown with the fan running aren't far off what you're suggesting.

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