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I guess summer is here... A/C questions are popping up...
I was waiting for hot days to try adding freon to my wife's car. (A/C system has developed a slow leak over the last few years and I had to add a can or two for hot summer months only to watch it gone the next spring. I've done this the past three years and was hoping I can get away with this once gain this year.) Well, last weekend I decided it was time. I had an extra can of freon and I have a manifold gauge which I use for refilling/adding freon though the low pressure side.
I started the car, turned A/C to max, closed windows, and connected manifold gauge to the low pressure side. The A/C compressor was cycling on/off every 4-5 seconds. The gauge showed the pressure between 20 and 45 psi during the cycling. But since the air lowing though the evnts was warm, I thought the I still needed to add freon. So I connected the can, pierced the opening in it, and opened the valve. I was waiting and waiting and waiting (maybe 15 minutes or so) but the readings on the gauge did not change: still between 20 and 45 psi and still cycling on/off every 4-5 seconds. Also, the can did not seem lighter -- I can feel gas inside the can. I figured the freon was not going in the system. As the last resort, I connect the can with freon directly to the low pressure side bypassing the manifold gauge. Still, after waiting for 10-15 minutes I did not notice that the can got any lighter. Why didn't A/C system accept any freon? I used exactly the same procedure the last three years and it was working just fine. What could be wrong this time? Any ideas?
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IT helps to monitor high side pressure when trying to characterize a malfunctioning system.
My guess is that maybe your orifice valve is blocked or just frozen (did you ever charge from empty without doing a vacuum first?).
Could also just be the heater control valve stuck and having coolant go through the heater core, heating up the air.
The low side pressure does not seem that bad but you can;t tell much without having a high side pressure reading. Careful - overcharging a system with r134 is easy and will cause poor performance. Compressor should likely cycle on 50% of the time (estimate) to indicate a proper charge.
Might be time for a new accumulator and new OV or VOV. Then a good deep vacuum and recharge.
Good luck,
Greg Mustang
Montreal - Ottawa
Canada
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I don't think I can connect to the high pressure side in S90. I believe I asked this question before and the answer I got was that S90 does not have the high pressure side port to connect to.
Am I correct assuming that since my compressor is cycling on/off the pressostat is working? (Otherwise the compressor would stay off all the time, correct?)
Can I troubleshoot the heater control valve? Where is it located? Also, how can I check if the orifice valve is blocked?
As I said in the pst two years I used the same procedure to add freon and it was working. According to some rapid cycling of compressor on/off with ambient temps at 80+ indicates a low charge of freon in the system. Is that correct?
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Correct, your S90 does not have a high pressure port for the AC.
The low side pressure with the A/C compressor cycling should be 23-45 psi which is what you have. Cycling time depends on outside temperature. Cooler temps have the compressor cycling more frequently. Hotter temps keep the compressor engauged longer.
The heater control valve is located on the firewall and has a samll vacuum line going to it. Check for vacuum and check for movement when your dashboard temp is moved from hot to cold.
If your system is working fine, your accumulator should still get cold and you can feel that whether or not your heater control valve is working properly.
It's hard to tell if the orifice valve is partially blocked without taking it out. If you haven't had any problems with the system such as a seized compressor that would distribute particles throughout the system, your orifice valce is probably o.k. .... Unless all the r134a you've been adding has a leak sealer in it. That stuff us bad news. The orifice in the valve is very small and can be plugged up with sealer gunk. I find it difficult ot find just plain R134a without any other bonus stuff added to it.
It is possible to overfill these systems. The only proper way to do it is to evacuate the entire system, repair leaks, then add only the required number of ounces to the system w/oil. But this is not alwyas possible in the home garage.
What's your system's static pressure with a cold engine at 75 degrees ambient?
DEWFPO
--
1998 S90 068,300 and 1995 964 152,300
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>> If your system is working fine, your accumulator should still get cold and you can feel that whether or not your heater control valve is working properly.
Hmm... The lines to/from accumulator do not get cold/sweety as they used to even when A/C is on on Max. So, this means that heater control valve is not my problem, correct?
>> What's your system's static pressure with a cold engine at 75 degrees ambient?
You mean with the engine and A/C off? I am gonna check it tonight. It should be about 70-75 degrees outside today.
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Just checked the pressure in the A/C system with the engine off: 85 psi. It was about 75 +/- 2 degrees tonight. With the engine running and A/C on Max the system (compressor) cycles on/off every 4 seconds and the pressure jumps between 21 and 45 psi. However, if I manually turn of the fan (set it to 0) the pressure rises to 85 psi and stays at 85 psi. So, what does it mean?
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RK,
I checked the static A/C pressure on both our 95 960 and our 98 S90 when the engines were cold (hadn't been driven all day) and it was ~75 degrees out. The pressures were 73 and 75 psi. Both systems cool just fine.
Your 85 psi does not sound far off if the temp was a little higher or if the engine compartment was still warm. If the car hadn't been driven all day, I might consider this a slight overcharge condition but it is hard to say.
If you set the fan to '0', then the compressor does not come on so you are checking static pressure again except with the engine running.
What temp do you have the ACC set at?
Have you checked the heater valve?
DEWFPO
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1998 S90 068,300 and 1995 964 152,300
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Isn't the relationsip between the amount of freon in the system and the low side pressure reversed? In other words, the less freon is in the system the higher the low side pressure is generated by compressor? Or am I wrong on this one? Anyway, static 85 psi was after the car was driven for about 30-40 minutes in traffic and then cooling in the garage for another 15-30 minutes. So, I would not call this as compltely cold engine.
Your comment about setting fan to '0' makes sense. Thanks.
When charging ACC dial was set all the way down, maximum cooling.
How do I check the heater valve?
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RK,
Based on your description of driving 30-40 mins and only a short cool down period (15-30 mins), I would have expected the static pressure to be higher than 85 psi. Biu I don't have a temp/psi chart.
If you consider that the compressor is sucking on one side and compressing on the other......... a low freon charge should create lower high side pressures and lower low side 'pressures'.
But I am not an expert.
To check your heater control valve, start your engine, put temp control to max heat, and check the position of the arm on the valve, now move your temp control to max cool and see if the arm has moved 90 degrees. If it hasn't, check for vacuum at the valve in both max cool and max hot positions. If no vacuum, trace your line and look for a leak. If you have vacuum and no rod movement, change out the valve.
DEWFPO
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1998 S90 067,100 and 1995 964 150,850
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>> To check your heater control valve, start your engine, put temp control to max heat, and check the position of the arm on the valve
Sounds pretty simple. But where is the heater control valve located and how it looks like? (As a reference, let's assume I am standing in front of the car with the hood open and staring at the shiny aluminum can/AC accumulator.)
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RK,
Against the firewall between the power brake booster and the engine on the driver's side is a silver metal plate with the two heater hose connections entering the firewall. At the bottom of that plate the heater control valve is attached. The heater hose comes into and out of the valve which is controlled by a small vacuum belows that actuates the valve itself.
DEWFPO
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1998 S90 067,100 and 1995 964 150,850
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Your description was excellent! I found it almost immediately.
The heater control valve's arm does move in my car when I change the temp control from max hot to max cold. However, I don't think it moves as much as 90 degrees. More like 45 degrees, maybe a little more. I don't think it can move 90 degrees: in both end position it seemed to that the arm movement was limited. (Are you sure it was supposed to move 90 degrees and not 45-60 degrees as I observed? In my case, at Max Heat the arm was in the vertical position, and at Max Cold it was at about 45 degree angle.)
Anyway, I am glad I did this test because it tells me that the heater control valve is probably not the problem. But what is?
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RK,
Your right, I never measured the degrees of movement of the arm on the heater control valve but it does appear to move only about 40 degrees or so. Since yours apprears to be operating just fine, that is probably not the problem.
At this point I'd probably take it to a professional. R134a systems are very sensitive about the correct amount of freon being in the system. My gut tells me it's slightly underfilled.
DEWFPO
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1998 S90 068,300 and 1995 964 152,300
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>> My gut tells me it's slightly underfilled.
That's what I think too. I just need to figure out why it is not taking any new freon. I think I will take my chnaces and play with it a little more. I am already thinking about getting a vacuum pump so that I can evacuate the what is left in the system and try recharging it from 0.
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posted by
someone claiming to be Chrissij
on
Fri Apr 23 05:51 CST 2004 [ RELATED]
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Sometimes the charge fitting is bad...it can't take it in with a bad fitting, and they are WAY cheap, and so easy to screw off and on.
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Are you talking about that thingy with a screw on it for piercing a hole in the R134a can? Mine came with the kit. I guess it is worth a shot... Where can I get them for cheap?
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posted by
someone claiming to be Chrissij
on
Sun Apr 25 07:06 CST 2004 [ RELATED]
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You should be able to get a low side charge fitting from any parts supply place, just take yours off, and have them get you one like it.
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If I take it off, will I "wet" the A/C system (open it to the air)?
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posted by
someone claiming to be Chrissij
on
Sun May 2 06:34 CST 2004 [ RELATED]
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Sorry for the delay, didn't see your question until now. Hopefully you've already done this, but no, you can just take off the old charge fitting and put on a new one without worry.
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posted by
someone claiming to be Chrissij
on
Sat Apr 24 08:31 CST 2004 [ RELATED]
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I mean the thingee on your accumulator that you attach the other thingee to.
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