Hi All,
Got a question. I have been doing some work on my ac. I vacumed it to 29 hg and it held (almost) at that point for 15 minutes. It dropped about 1.5 hg then held for another 10 min.
Does this mean I have a leak some where that NEEDS REPAIR? I had read some where that a 10% drop was ok and this delta falls within that category. I am looking for confirmation on this.
Thanks in advance
al
There should be no drop in pressure at all if the system is sealed.
Tester
ok thanks I will re check the dryer and liquid line attachments again which I recently replaced.
Regards
If you left the vacuum pump hooked up and just turned off because you are using the gauge on it, it could be leaking through the vacuum pump itself and not the system.
+1 for what Keith said
Did you turn off the valves on the gauge set when you turned off the pump? You probably know that the gauges will read pressure with the valves closed.
I ended up fixing my A/C twice, when (I thought) that my only leak was a discharge hose. The vacuum held for a half hour, but I suspected the vacuum had dropped a little. As it turned out, my pressure switch was leaking at the electrical terminals.
The second time I pulled a vacuum, I left the gauge set attached for a week before filling system.
You may have a leak somewhere. (or if you left the valves open, try closing them and check vacuum again.)
Oh, BTW: If your dryer has flare fittings, they could be troublesome. The shop owner who made up my new discharge hose gave me a flare-shape washer to put on between A/C line from the condenser and the receiver/drier. I had a leak there too.
I just purchased the pump I don’t think it could be that.because last week after the install the vacuum held just fine doing the same. I have a habit that I always end up doing things twice in my life. I am going to check again tonight leaving it run for at least 45 min to dry it out then let it hold for an hour to see what happens.
I will keep you informed.
Regards
I can’t quite remember but thinking about that aspect I will make sure to do so when I test again tonight.
thanks for the advice
al
Hi Tom,
Well I worked the truck this evening. This is what I found and I think I need a new compressor.
At 1000 rpms the compressor reading read 160 lbs
At 2000 rpms the compressor reading read 175 lbs
At 2000 rpms you would be traveling about 80+ miles per hour which I don’t do.
I know it is not the system working with the vacuum pump. I ran it for 45 min and got it to 30hg. In this order
I closed the manifold which cut off the vacuum from the pump and shut the pump off.
I left the couplers open position
The vacuum held at 30hg for 45 minutes
So I don’t think it was my worksmenship in installing the dry and return line.
What do you think?
Thanks in advance for any advice you can give or suggest.
Regards
al
Hi Keith,
Well I worked the truck this evening. This is what I found and I think I need a new compressor.
At 1000 rpms the compressor reading read 160 lbs
At 2000 rpms the compressor reading read 175 lbs
At 2000 rpms you would be traveling about 80+ miles per hour which I don’t do.
I know it is not the system leak working with the vacuum pump. I ran it for 45 min and got it to 30hg. In this order after getting ready to shut pump off:
I closed the manifold which cut off the vacuum from the pump and shut the pump off.
I left the couplers open position
The vacuum held at 30hg for 45 minutes
So I don’t think it was my worksmenship in installing the dryer and return line.
What do you think?
Thanks in advance for any advice you can give or suggest.
Regards
al
If the vacuum held for 45 minutes then I don’t think you have a leak.
When you say “compressor reading” I assume you mean the high side. You wouldn’t want that on the low side, for sure.
Pressures vary according to the ambient temperature. If it’s hot (above 85 or so) , then yes, those pressures are low.
What were he low side readings?
Did you weigh the refrigerant when you charged it?
Knowing both high and low pressures can aid in diagnosis. If both low and high sides are low, that could be low refrigerant charge. If, for example, the low pressure side reads high, and the high pressure side is low (as in your case), then yes, it could be a compressor. It could be a bad expansion valve, the valve would be stuck open with that low high side reading.
Good Morning Tom
To answer you questions. Yes those were the high side readings.
As for the low side. When I tried to fill the system it would only take about 12 oz (on can) and only would barely read 20 lb or less. At that time the ambient air temp was about 90 degrees outside and not so humid.
As for the term “wet” I don’t know what you mean by that term. A brief explanation would do.
No I didn’t weigh the refrigerant
After I had finished with the first can for some reason when I moved to the next can it would not take anymore refrigerant. I paid attention to the manifold gauges making sure the high side was shut off. Before removing the can now that I think of it should I have closed the manifold on the low side before switching cans?
Also here is another issue the manual said to look for the decal that reveals the AMOUNT OF REFRIGERANT that would fill the system. I looked high and low on the truck Dodge dakota 2005 and could not find it so I am guessing here as to the proper amount. I figured a 20 oz can would suffice.
Thanks for your guidance on this.
Regards
al
Morning Tom
Some additional information.
I reviewed an auto diagnostic chart and based on my situation low side is low and high side is low at 90 degrees 45-55 Low / 250-270 High
Actual was 20 psi / 170 psi
The chart recommends adding refrigerant.
I will try re filling with more refrigerant today and see if it will take more.
I will send you the results tonight.
Thanks for your help
al
YES!!! You may have introduced air into the system.
But if you are going to replace the compressor, no harm done.
You should flush out the condenser. Shards of metal from the compressor may have entered.
If it were me, I would use a shop for this. I had repaired the A/C on my 1979 Toyota Celica two years ago successfully, as nobody wanted to take the job, as 1) it uses R12, 2) Too many things wrong -needed discharge hose rebuilt and once done, there was still a leak (turned out to be the pressure switch casing as described above).
Many people here say that DIY A/C repair is not a DIY thing. I agree 100%. I tackled it on my own, but it was A JOB!. My gauge set has fittings for 134a systems as well as R12. I believe that that one is defective, as the quick disconnect mechanism does not work. I won’t even get a new one, as if my other R134a car ('95 Toyota Avalon) ever needs A/C service, I will take it to a shop.
Good luck.
Morning
I started off with the system evacuated at 30hg. I will take your suggestion about the shards in the condenser into consideration.
So that is why the second can refused to dispense refrigerant into the system. It was already filled up with air. Now that makes sense to me.
It is amazing what a little collaberation will do and I thank you for this.
I will start over on this process.
Like you I ask the question can I complete this job before I do it. If my answer is no it goes to the shop if yes I will do it since I was a diesel mechanic 20 years ago. I like my tools still. Currently I am slowly rebuilding my truck since I have the capability to do so. I refuse to pay that $45k for a new truck. I had done the brakes and had the emission control system replaced. I did the computer myself since it didn’t need a shop.
Again thanks for all your help
al
I’ve been an AC tech for almost 40 years, and from the sound of things, neither one of you know what you’re doing.
I recommend you take the vehicle to a shop to have the AC system tested/repaired before you start replacing parts that may not be needed.
Tester
If the system is under pressure there is no way for air to enter the A/C system. If there was only 20 PSI on the low side and you were unable to add more refrigerant, you didn’t open the valve on the gauge set or you didn’t puncture the can.
Hi Nevada
After further thought I believe you are correct. I think I did make that mistake with the dials. I am starting from square one with a vacuum before adding refrig. I am taking it to the shop to evacuate what freon that is in there today before I start.
Regards
al
Yes, but when switching from can to can, are you not supposed to close the low pressure valve, and after connecting the second can, purge the service (yellow) line of air before opening up the valve again??? I think so. That’s what I was getting at.
Yes that is in my list of steps to do this time. I thought I had followed that the first time but unfortunately I guess I didn’t pay attention to what I was doing.
Regards
I was replying to Nevada_545.
Most of the possible causes of your displayed pressure readings I took verbatim from the 1995 Toyota Avalon Repair manual, namely pages AC14- AC19 in the back. But before I get described as not knowing what I am doing by others, I suggest you take your car to a shop…