2nd Gen Non-Engine/Transmission Air Conditioner Recharge??

[SLightfoot]

Hi folks.



For the past year, my AC has gone from very weak to almost non-existant. It started early last year, when it seemed to take a much longer time to start blowing cold air.



Now it hardly blows cold whatsoever after any length of time running.



We're about to head for a trip into a very warm area, and we're not gonna survive without this, so... .



What do you guys think - possible AC recharge required?



What is the normal intervals between recharges for these trucks?



Mine is a '99.



Thanks,



Shawn

 

[B.G. Smith]

There is really not a normal interval for recharge. Some run several years, others only a few. Sounds like you just have a slow leak. All compressors are prone to leak at the shaft seal a little and more so when not used much. I added some refrigerant to mine last season and it is still doing fine. Hope you are as lucky. Have someone who is competent in A/C service check the refrigerant charge, these units with the 134-a are more sensative to correct charge than the old F-12s were, a litle too much really reduces the cooling abality. bg

 

[Jdonoghue]

Might just need a recharge, these systems are very finicky about how much charge they have - just a little low will make a BIG difference in the output of cold air. My '01 has a leak in the schrader valve on the low side. Every three months or so I have had to put one can of R134A in it. I bought the tools (charging manifold) and cans of R134A at Autozone. Was cheaper than constantly taking it in to have it recharged until I could afford to replace the hose (the valve is not replaceable). Also, quite a few people have had their evaporator core corrode and leak the refrigerant out. Do a search for evaporator and I'll bet you'll find quite a few posts.

 

[ceastmen]

Jdonoghue,

Where do you add the R134A, I would like to add a small amount to help out my truck it doesn't work as well as it did last year.

Thanks Chuck E.

 

[Jdonoghue]

R134A is added to the low side port, which is on the line near the turbo. Never connect the charging can to the high side (the one near the battery) - the can will probably explode. I used an A/C manifold gauge set when I did mine, it connects to both ports and allows you to see the pressure on both sides while charging.

 

[SLightfoot]

OK- I'm taking it to a shop in a couple of hours to get them to have a look at it.



I suspect that it's just low on charge, since the AC clutch keeps cycling on and off every 7 seconds, which I've heard is the classic sign of low refrigerant.



I'll let you know what happens.



Thanks guys,



Shawn

 

[Kawi600]

Anyone know what pressure you should see on the low side (the coupling nearest to the radiator I think) with the motor running and AC on?

I got the figure 25-45 from somewhere but wasnt 100% on that.

This is on a 95, dunno how similar the setup is to '99. Ive also got the same symptoms, rapid clutch cycling and cool air only.

 

[B.G. Smith]

25# to 43# is the operating range of the clutch cycling switch with 134-A. If the unit had the right amount of refrigerant then you should see 35-40# suction pressure or even more if the outside temp. is high until the truck is cool inside. If it is cycling on and off then it could indicate that the unit is low on refrigerant. Just be sure you hook up to the right (suction) line and don't overcharge, mine (99) only holds 28 oz. bg.

 

[SLightfoot]

OK folks-



It was indeed very low in refrigerant. They recharged it at the shop a couple hours ago. Blows so cold - I forgot how cold it could be.



They also added a dye to it - just in case there is a leak - they will be able to spot it later. They said it was about right for recharge - some folks are only getting 1-2 years out of 'em they said.



We'll see how she goes.....



Shawn

 

[Nate]

Mine didn't seem all that cold, but I just checked it and it's holding steady just under 40psi.

 

[WadePatton]

The a/c never needs a recharge until the 134 leaks out. My 24v hasn't been charged since I've owned it--little over 140k on the clock. The Green Thing hasn't been charged since the evaporater was replaced years ago. BUT the Big Red had been taking a charge at ever shorter intervals--until the last time, which only went a few miles...



AND (don't do this) I had dumped a can of "stop leak" into the system. That is a no-no, because most everybody (modern shops) uses a closed loop system to work on A/C and they don't want that stuff in it--it has a red dye. It's a leftover product from the R12 days and I had to run down a old-style vacuum pump to get the system pulled down.



The evaporator tends to start leaking on these trucks because of lack of support. It's a big job R&Ring one.



Good luck.

 

[georgej]

I usually add a can per year. It seems to last all summer when the AC is used but slowly leaks out through the evaporator during the winter. I generally stick a temperature probe in the middle vent and slowly add r-134 until it reads about 45* and the proper psi in the system(temperature dependent). This is the only ongoing issue with my truck and if I wasn't so cheap I'd fix it right

 

[fest3er]

25# to 43# is the operating range of the clutch cycling switch with 134-A. If the unit had the right amount of refrigerant then you should see 35-40# suction pressure or even more if the outside temp. is high until the truck is cool inside. If it is cycling on and off then it could indicate that the unit is low on refrigerant. Just be sure you hook up to the right (suction) line and don't overcharge, mine (99) only holds 28 oz. bg.

To be a tad clearer, with the right amount of R134A, 85F+ outside, 80%+ humidity, system on fresh air, fan on high and engine at around 1200 RPM, the low pressure side should pull down to maybe 30 PSI and stay there, and the compressor should not cycle off (because maximum demand is placed on the system). Then if you turn the fan to low speed, the compressor should start cycling (because little demand is placed on the system). I've simply added freon until the compressor stops cycling. 9. 5 years, 235K miles and I've never had the A/C apart; I think a re-seal is due.



BTW, the high pressure and low pressure couplings are different sizes, so if you buy a recharge kit at your local store, it should be nigh on impossible to connect it to the high pressure port.



N

 

[Cliffman]

Okay, I've added 30oz in a 32oz system. My low pressure drops to 25psi and then the compressor cycles off. I have very good cooling now but why is the pressure still dropping past 25psi?

 

[B.G. Smith]

What is the temperature outside? It probably is fine, just not much heat load. If you still have your gages hooked up, try opening both doors and put the ac blower on high. bg