What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

A/C's 202....

rjfguitar

rjfguitar

3/4 ton status
GMOTM Winner
Joined
Aug 28, 2002
Posts
9,120
Reaction score
175
Location
california
I converted my '81 Crew cab over to R134A and am experiencing poor A/C performance.

New pump (not a reman), dryer, orifice, and TAG oil. I put 2.82lbs of R134A in the system and am having issues with the pump cycling quickly with the RPM's of the engine raised. At idle, the pump stays engaged continuously, but once I rev it up it cycles every 15 seconds or so. it acts like it's low on freeon but 2.82lbs is probably a little too much, IIRC the older systems can't hold as much R134A as it does R12 right?


My questions would be that those of you guys that have converted your early A/C systems (systems that use the long "hot dog" pump), how did it behave with R134A and what kind of vent temps do you have. Mine are between 50-70* depending on ambient temp, and it wants to stay cooler when the RPM's are low. When it cycles too fast it isn't getting pumped enough at higher RPM, which is what I'm thinking anyway.

My pressures are between 30-35psi on the low side and 200-250 on the high side.
 
how much r12 did it hold originally? times that by .9 and thats how much 134 it holds too much is just as bad as too little
 
There is an adjustment on the low pressure switch just under the connector. Try adjustiing the low pressure switch so to where it disengages at about 25 lbs and see how that acts. Your pressures and charge level seem about right you just need to get the low side pressure to go down a little lower for it to stay cold. If the compressor still cycles more than every 25 seconds or so then try adding another 0.2 lbs. and see how it acts. Just be careful the high side doesn't get over 270 psi or so, those old compressors don't live very long when the high side pressure gets over that. Make sure your clutch fan is working good as well, you may want to add an aux. pusher fan just for added insurance.
 
bigblock72 said:
There is an adjustment on the low pressure switch just under the connector. Try adjustiing the low pressure switch so to where it disengages at about 25 lbs and see how that acts.
Click to expand...

Where is this adjustment at? I looked but can't really see anything obvious to adjust.
 
Most R134 systems use a fan that comes on at 225psi and off at 175psi. Connect the pressure switch to the high side line, have the switch control a 30A relay that turns on / off a pusher fan. The NAPA Eclin parts line would have the pressure switch you need.
And yes, R134 is not as efficient as R12. If you looked at the vent ducts on R134 vehicles you will notice that they are bigger ( some also had AC ducts at the rear of the center console ). The fan speed was increased to move more air.
The pusher fan in front of the condenser increased the condenser eficiency and reduced the load ( pressure ) on the compresser. This reduced (hi) pressure helps make COLDER air for the cabin.
 
rjfguitar said:
Where is this adjustment at? I looked but can't really see anything obvious to adjust.
Click to expand...
You have to unscrew the pressure switch from the receiver/dryer can and hope the schrader valve in there is good. I don't remember if they take a little flat-head or an allen wrench, but you adjust it and then use the gauge to tell you where it is set to.

Don't you have electric fans? How deep of a vacuum was used to evacuate the system and how long was it left under vacuum?
 
Oh yeah, what kind of orifice tube did you put in? I can't remember which one flows faster, R-12 or R-134.
 
The adjustment is under the electrical connector, unplug it and you'll see a flathead screw between the two terminals, back that screw out about a half a turn. The low pressure switch is the one on the accumulator.

R134 retrofit systems usually work best with a big orifice tube or even a variable orifice tube. The bigger orifice will help move more volume through the evaporator which will help keep the high side pressure down as well as keep the a/c cold on super hot/humid days.
 
alternative to 134a

This is what I would use instead of 134a when I can find it around here you still have to retro fit the ports(all I do) and works for me,Works great!! Nice and cold.http://www.freeze-12.com/
Read down you will find the automotive cans and a q&a area


Mike
 
Refrigerant blends are bad news, law requires special freeze 12 only fittings be installed. Then there are issues of different leak rates of the different refrigerants in the blend, i.e. one refrigerant can leak out faster than the others and alter the characteristics of the blend and therefore the cooling abilities. Bottom line is only use R12 and R134 in your automotice a/c system and save us all some serious headaches.
 
Freeze 12 is propane. It does work good but is highly flammable. If you don't smoke there is no problem. If you have a leak in the evaporator ( many GM vehicles from 78 and newer did ) and someone lit up a ciggarette in the cab with the AC running it would flash and burn like gassoline. FYI
 
Freeze 12 is not propane! It's a mixture of 80% tetraflouroethane and 20%chlorodiflouroethane refrigerants and is non flammable.
 
No, but you can use propane. I guess you can mix propane and isobutane in the right ratio and replace R-12 with it. Flammable? Yes, but it's been done many times. It's really only an issue in an accident or some other catastrophric failure. But then again, so is pressurized gasoline.

But back to the topic - If you are going to open up your system again, you might try the VOV, they are affordable and do help a little.
 
Sorry about that . I must have confused Freeze 12 with OZ 12. On a side note how can chlorodifluoroethane be acceptable when it has chlorine in it ( Freeze 12 )?
 
Blue85 said:
You have to unscrew the pressure switch from the receiver/dryer can and hope the schrader valve in there is good. I don't remember if they take a little flat-head or an allen wrench, but you adjust it and then use the gauge to tell you where it is set to.

Don't you have electric fans? How deep of a vacuum was used to evacuate the system and how long was it left under vacuum?
Click to expand...

I'll check the plug and switch out. I have electric fans on my K5.

This is on my K30 CC service truck that has the stock fan.
 
mdm365 said:
This is what I would use instead of 134a when I can find it around here you still have to retro fit the ports(all I do) and works for me,Works great!! Nice and cold.http://www.freeze-12.com/
Read down you will find the automotive cans and a q&a area


Mike
Click to expand...

I've got a 30lb bottle of freeze 12. It's ok stuff, R12 still works better though. When I had Freeze 12 in this same vehicle it didn't do much better than R134A, and 134 is cheaper.
 
You must log in or register to reply here.

Latest Posts

Top Bottom