2nd Gen Non-Engine/Transmission AC Problems??

[Texis]

The 97 has had a slow Freon leak for years, every 6 months... add a can. But the trick didn't work today. After adding a can,
the system is cycling from 25-55psi on the LP side (normal), clutch is engaging and everything sounds and appears normal.. BUT no cold air!

The air is blowing, just hot. Not acceptable in Southeast Texas, but this late in the heat season I hate to spend money on the AC.. Any ideas??
I will add that the Freon can never really got cold while I added it? Didn't seem normal at all, typically they get fairly cold when discharging the Freon. Is it possible the can was defective? I have pondered bleeding some off and putting another can in it?

Thanks

 

[Bill Stockard]

The 97 has had a slow Freon leak for years, every 6 months... add a can. But the trick didn't work today. After adding a can,
the system is cycling from 25-55psi on the LP side (normal), clutch is engaging and everything sounds and appears normal.. BUT no cold air!

The air is blowing, just hot. Not acceptable in Southeast Texas, but this late in the heat season I hate to spend money on the AC.. Any ideas??
I will add that the Freon can never really got cold while I added it? Didn't seem normal at all, typically they get fairly cold when discharging the Freon. Is it possible the can was defective? I have pondered bleeding some off and putting another can in it?

Thanks

What pressure are you seeing on the high side?

Bill

 

[Texis]

I have not checked the high side, what pressure should it run?

 

[JR]

Be very careful about adding Freon without knowing 100% sure you are low. You can cause a lot of damage in a hurry by over pressuring the system. What are you checking your pressure with? Most gauge sets will have a temperature/pressure chart. A/C pressures are largely related to ambient temperature. I have a chart but my cousin has my gauges at the moment so I can't copy it for you. The general rule of thumb for high side pressure is 2.2 - 2.5 times the ambient temperature. So if it is 90* ambient temp, your high side pressure should be roughly 195-225. This is just a guideline, and not necessarily conclusive that you are low on refridgerant if your pressures are lower than stated. Lots of other factors to take into consideration but pressures are a good place to start. When you took the low side reading do you remember what the temperature was? 55psi is approaching the high side of what you should see unless it was over 100* out when you tested it.

 

[Jeff L]

"..the Freon can never really got cold while I added it? Didn't seem normal at all, typically they get fairly cold when discharging the Freon..."
-Texis


You sure you added freon, and not oil?

Just a thought.

 

[Texis]

Update..

OK, so the truck has been parked (once a week driven) for the past 6 months. Didn't need it last winter and it is not the daily driver. I finally got around to checking the high pressure side of the system. BTW I'm thinking about returning "ole reliable" to DD status, so this needs fixin.

Here's what the AC is doing:

1) Compressor engages and stays engaged about 3 seconds, then disengages.
2) Low pressure side runs 25-50 during this 3 second cycle not sure if it peaks at 50, still climbing when the compressor clutch disengages.
3) High pressure side runs 100 - 140 during the 3 second cycle, appears to peak at 140 as it stabilizes at 140 ish.. then compressor clutch disengages.
4) Low pressure line is cool, compressor is not on long enough to get it cold, but the temp drops while compressor is engaged.
5) AC relay is good, I have tried several and get the same results every time.
6) Outside temps when tested 90-93F (as always in Texas)

So, if you guys are saying high pressure side should be 195-225 then I am definitely well below that. Don't believe I am low on Freon based on LP reading, so the low Freon switch "should not" on the accumulator should not be disengaging the compressor clutch. It DOES cool through the vents for the brief 3 seconds that the compressor is engaged. Gauges are basic O'Reilly AC shelf stock gauges i.e. not high end stuff, but they appear to work OK.

What's next?

Thanks in advance.

 

[B.G. Smith]

The pressure switch on the accumulator opens(stops compressor) at 26#, it closes at about 44#. sounds like still low on 134? It is very difficult, at least for me to get the correct amount of charge in the system by reading the gauges. bg >

 

[Texis]

The clutch compressor clutch kicks in at around 25lbs on the low pressure side and the compressor clutch disengages around 50lbs. So once engaged, the compressor builds pressure up to 50, then kicks out.. cycles down to 25 and re-engages. So compressor stops (clutch trips out) at 50.

BTW 55 is the max safe psi on the gauge (green zone). Above 55 is in the red. I hate to just keep adding based on my current numbers, I am already near the red?

 

[B.G. Smith]

It's about 93 outside, with nothing running you should see around 110# on your gauge. Start truck and turn on AC, gauge pressure should start to fall but should stay above 26# if fully charged until things get pretty cool inside the cab. When the pressure drops to 26# or lower the compressor will stop and the pressure will rise until it gets above 44# and then the compressor will restart. bg

 

[DavidC]

As stated above, filling with gauges is a guessing game. I have made systems operational by jumping the low pressure switch while filling to where I have 30-35 constant on the low side on max AC with the windows open. It is not a precise fill as you would have to have an empty system to do that.

Dave

 

[Texis]

So the pressure drops when the compressor is running? The 110 psi you are describing is constant with the engine turn off? This is the low pressure side?

BTW Port Neches is pretty darn close to Little Cypress.. so the 93 degrees you mentioned is dead on lol and you are well aware of how badly I need AC if I want to use my truck in our area!

 

[fest3er]

The clutch compressor clutch kicks in at around 25lbs on the low pressure side and the compressor clutch disengages around 50lbs. So once engaged, the compressor builds pressure up to 50, then kicks out.. cycles down to 25 and re-engages. So compressor stops (clutch trips out) at 50.

BTW 55 is the max safe psi on the gauge (green zone). Above 55 is in the red. I hate to just keep adding based on my current numbers, I am already near the red?

If it only takes three seconds to drop from 50PSI to 25PSI, you are still low on R134. Run the engine, start the A/C, then add R134 to the low pressure side (only place the connector will fit). It should take 10-20 seconds (maybe more, it might depend on the outside temp) for the compressor to suck the low pressure side down to about 23 PSI.

If you put a little too much R134 in, the inside air will be colder but might be too cold when it's 25°F-45°F outside; in this case, the A/C won't run long enough to dry the air enough to effectively defrog the windscreen.

If you put more more than a little too much in, the outlet air will be delightfully frigid and you may find that the low pressure side finds a steady state between 30 PSI and 45 PSI where the compressor never stops.

My '98's evap leaked from the factory. I just kept adding R134 it for 15 years. Finally that trick stopped working and I had to replace the evap. Had the mechanic pull a vacuum for the requisite hour or so, then he filled it. I think I had him add two ounces extra. It's been running fine since. No leaks, but it doesn't defrog very well when it's quite chilly and humid outside; I might have him pull an ounce out.

 

[Texis]

Thanks for all the responses. Sounds like I need more R134.
I purchased the truck in 2002, it needed an evaporator core at the time (pouring R134 out of the vents). I had it replaced at that time and besides the occasional clutch, have had very few problems with the AC. It still has "some" R134 in it from last fall, so I assume the evaporator is not bad or it would have lost all it's R134. I'm betting some of the tubing O-ring fittings are leaking a bit, they are 18 years old!

I'll try adding a can "or so" of R134 tomorrow.

BTW>>> why do they caution so much about putting too much R134 in the system. A little reading and you would think the thing will explode if it has too much!

 

[fest3er]

Just jumper the high pressure connector, run the A/C and wait a few seconds. You may need to change your shorts after a *very* loud unknown sound issues from the engine compartment. Don't ask why I know this.

There *is* a relatively fine balance point. Too little R134 and the clutch will cycle a lot and the air won't be cold. Way too much and the clutch may cycle a lot and the air may be entirely too cold (that is, the evap could freeze up too often).

I'll bet you won't fit in a ½ can more before it starts working better. It's close because the clutch does cycle.

 

[JR]

If it only takes three seconds to drop from 50PSI to 25PSI, you are still low on R134.

His compressor is climbing to 50 psi and then kicking out.

 

[DavidC]

So the pressure drops when the compressor is running? The 110 psi you are describing is constant with the engine turn off? This is the low pressure side?

BTW Port Neches is pretty darn close to Little Cypress.. so the 93 degrees you mentioned is dead on lol and you are well aware of how badly I need AC if I want to use my truck in our area!

Yes the low side drops with compressor running then shuts off in the 20's with low pressure switch. When the engine is off pressures will be the same on low and high as they equalize.

Dave

 

[fest3er]

His compressor is climbing to 50 psi and then kicking out.

(I had his wrong for a long time, too, until someone explained it clearly. Then A/C operation became obvious.)

As David noted, the compressor sucks a vacuum on the low pressure side as it pumps everything to the high pressure side. So the low side pressure drops until the low pressure switch opens which releases the clutch and disengages the compressor. Then the low side pressure floats back up to around 50 PSI as R134 on the high pressure side flows into the evaporator and 'refills' the low side. At around 50 PSI, the low pressure switch closes and the compressor clutch engages again. And the compressor cycle begins anew.

After the compressor does its thing, the R134 is still gaseous. When it passes through the condensor, the heat extracted from the cab and the heat of compression are removed and the R134 re-liquifies and passes in liquid form to the evaporator where it begins the heat extraction cycle all over.

Were the system designed a little differently, it could just as easily reverse the flow and pump heat from outside into the cab. This wold be nice to have on those wintry days before the engine has worked hard enough to heat up.

 

[Texis]

1 can did the trick. Hate to think I the truck sat around not being used much this summer over 1 can of Freon!! Live and learn. Seems to be easier and more accurate to pay attention to what the compressor is doing vs trying to get the pressures right. After 1 can, the compressor stays on for 30-45 seconds, then kicks off for 5-6 seconds. Sounds, looks and acts right enough for me.

Go me so excited I started working on the next project, which will be finally getting some more horse power out of this engine. Had the cat removed today as step one.

Thanks