recharging a/c...reading the gauge correctly (2011, replace, head)
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I'm topping off my a/c with a DIY kit, but the gauge reads different pressures depending on whether the compressor is running.
Am I supposed to use the lower reading when the clutch is engaged, or the higher reading when it's not?
(Other info: It seems to cycle on again too fast, so I wonder if is still undercharged. Also, I don't think there are leaks in the system - it's just a bit low because I let some R134a out, for reasons I won't go into. )
Read system operating pressures when the A/C compressor clutch is engaged.
Use your other senses to check out the system ... you should be able to feel sharp cold temps at the low side line into the compressor, as well as heat at the outlet (high pressure) side (use common sense here ... you don't need to grab the line in a death grip, but brush past it to feel the heat). You should feel heat at the condensor, too. And finally, you should feel sharply cold air at the outlets in the car with the compressor cycling "normally" as you have heard and felt it in the past when the system was operating correctly.
Roll down the car windows. Turn the A/C fan on high and A/C on. This will keep the compressor running or running longer.
Then the low side pressure (compressor running) should be as indicated on the following chart, which depends on what the outside temperature is (pressures are higher with higher outside temperatures)... http://idqusa.com/wp-content/uploads...art-33776F.jpg
Am I supposed to use the lower reading when the clutch is engaged, or the higher reading when it's not?
You are supposed to use the lower reading when the clutch is engaged and the refrigerant is circulating thru the system.
However you don't have all the tools you really need with the DIY kits. You also need a high pressure side gauge, something the DIY kits do not have.
It is normal for the low side to spike high in psi when the compressor is off and drop when it is on.
If your compressor is coming on, then kicking off, then coming on again, it means you do not have enough pressure in the low pressure side to sustain the switch being closed, which in turn disengages the compressor clutch until the psi builds up, then it comes on again.
Also....did all of your refrigerant leak out? Or just enough to cause it to short cycle?
When those kits themselves don't leak, we call them grenades.
I've read enough about where those cans got hooked up and overpressured and really hot, which is not something you want to do with a nerve agent sitting in them.
Either way, let us know how your shop visit goes...
REITERATE; Those DIY kits are pretty worthless. You need to have a high and a low gauge to properly charge an A/C system.
From a professional technical standpoint, knowing all the issues that can befall an A/C system ... absolutely correct.
But this OP states that for reasons not posted, he bled off some of the refriegerant from an otherwise properly functioning system. So a modest top-off could restore the system to proper operation as evidenced by a low-pressure gauge reading in a normal range and cold air coming out of the ducts.
Would the "repair" be as competently and professionally correct as if this was done in a shop with correct use of gauges and a thorough inspection of the system? No.
But could it suffice for the OP's needs to just top off the system? Yes.
What's the worst case scenario as a result? The OP doesn't get the system operating properly and has to bring it into a shop? That's a pretty modest gamble to take ... $20-30 worth of D-I-Y kit vs an hour or more of a pro shop testing the operation of the HVAC system ....
Today, it hit 85 in Denver so I fired up the AC. After 15 minutes of driving with AC on max, the gauge was steady, reading 15-25 psi low according to the ambient temperature pressure chart on the can. The clutch was engaged continuously while reading the pressure. I dumped in the rest of the can and the air is now much colder.I'll finish off the can tomorrow if the pressure still reads low and update.
One person asked if I had drained the whole system. The answer is no; there was still pressure in the system when I started. Thanks everybody for the great responses.
From a professional technical standpoint, knowing all the issues that can befall an A/C system ... absolutely correct.
But this OP states that for reasons not posted, he bled off some of the refriegerant from an otherwise properly functioning system. So a modest top-off could restore the system to proper operation as evidenced by a low-pressure gauge reading in a normal range and cold air coming out of the ducts.
Would the "repair" be as competently and professionally correct as if this was done in a shop with correct use of gauges and a thorough inspection of the system? No.
But could it suffice for the OP's needs to just top off the system? Yes.
What's the worst case scenario as a result? The OP doesn't get the system operating properly and has to bring it into a shop? That's a pretty modest gamble to take ... $20-30 worth of D-I-Y kit vs an hour or more of a pro shop testing the operation of the HVAC system ....
I'm really not trying to match wits with you here. This is nothing more than pertinent info.
You have roughly the same years as I. There will be others seeking info that will read this post.
With the inefficiency of 134a and the balancing act it takes with some cars to obtain proper cooling and performance, you know as well as I do that head pressure is very important. Personally, if I had the choice of the two gauges I'd take the high side. We are no longer in the days of sight glasses and $1 freon. All it takes is a half can to send the high side pressures through the roof. I would have a hard time trusting these gauges as I have had to replace a couple of professional units in the past.
Let's say, some DIYer takes the compressor loose without discharging and loses the bulk of the oil. Then recharges assuming oil is in the can too. This can be quite costly these days. Not to mention the guy that assumes he needs to add oil with the charge every time and oil saturates the system unknowingly.There are too many variables at hand.
Again, you are experienced and so are some others, and we have a general idea of what to expect and look for. We just need to keep in mind that a lot of people may be looking here for answers. We need to make sure they are aware of the different circumstances that they may encounter.
JMHO
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