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1990 k5 A/C Question

Justin Fleming

Justin Fleming

1/2 ton status
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Aug 24, 2005
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Location
Oxford MI
So I have been doing soem reading and I am not sure what the problem is. System has a new condensor, orings, dryer. When hooking gauges up and attempting to fill the system.... my low side pressure is now reading about 90 and the high side is reading about 90. when I engauge the clutch the low side comes down to about 50 and the high side does not move. From reading they referr me to a stuck expansion vavle??? I dont see anything that fits this discription in our ac system? Am i missing something here?
 
Justin Fleming said:
So I have been doing soem reading and I am not sure what the problem is. System has a new condensor, orings, dryer. When hooking gauges up and attempting to fill the system.... my low side pressure is now reading about 90 and the high side is reading about 90. when I engauge the clutch the low side comes down to about 50 and the high side does not move. From reading they referr me to a stuck expansion vavle??? I dont see anything that fits this discription in our ac system? Am i missing something here?
Click to expand...

With the gauge manafold closed, and when I engage the clutch it will pull the low side down to around 8 and the high side climbse to about 125. Somethign seems real odd here....

Is this possible due to maybe the old R12 was not evacuated properly? When I got the truck it already had the R134 adapters on it so I do not have the history.....

When I replaced everything the truck held a vaccum for days with out and leakage.....
 
Not much to go on there. We never open the high side ever unless we're vaccuming, just saying. How much 134 did you put in thru the low side. Do you have the low switch jumpered? Shouldn't run at 8 psi

You said 90/90 then 8/125???
 
If you have both high and low lines hooked up, and you open the manifold valves, the output from the compressor will go through the manifold to the low side bypassing most of the system and the pressure will be pretty much equal.

8/125 sounds about right for a system that is low on gas. But the pressure switch should kick off the compressor before it gets that low like Blazer74 said.
 
Fordum said:
If you have both high and low lines hooked up, and you open the manifold valves, the output from the compressor will go through the manifold to the low side bypassing most of the system and the pressure will be pretty much equal.

8/125 sounds about right for a system that is low on gas. But the pressure switch should kick off the compressor before it gets that low like Blazer74 said.
Click to expand...

I was manually bypassing the pressure switch...

I only got about 1.5 pounds in the system, I am now wondering is I should start over and drain the system down and put the system under a vaccum again? It seems as there is to much pressure on the low side and that was making me nervus.
 
blazer74 said:
Not much to go on there. We never open the high side ever unless we're vaccuming, just saying. How much 134 did you put in thru the low side. Do you have the low switch jumpered? Shouldn't run at 8 psi

You said 90/90 then 8/125???
Click to expand...

So I only got about 1.5 pounds in system through the low side. Just to be clear I did not ever open the high side when filling. At one point I did have the 134 vavle shut off and I did open both manafold valves red/blue just to see what was going on. When doing this did I introduce a bunch of the pressure to the low side by doing this? Should I drain the system down and start over?
 
I'd add another can a see what you get, 8/125 is ok, but don't open the high side with the system running. With the system off pressures will equalize hi and low
 
Leave the red valve completely alone, do not open it, leave it closed. Only use the high side gauge to watch the high pressures.

Add another can of freon, low side 50ish, if I remember right, I could have sworn the high was supposed to be up around 200-250 or so. I'm sure I'll be corrected if it's wrong though.

It's been a long while now since I have really messed with the ac system.
 
Approx 80% of original r12 charge is what is required.
You may need to put a high capacity fan in front of grill to keep hi side temp/press down due to low airflow at idle or hit the condenser with a water hose briefly.
Depends on temp and humidity where your at.

Hi side pressures in excess of 300 should be avoided. Extended idling will cause hi pressures.

Pancake style compressor I'm guessing three cans it should be cooling, add slowly and check temps often. Placing the can in a container of warm water will speed up transfer of freon into system if needed
 
blazer74 said:
Approx 80% of original r12 charge is what is required.
You may need to put a high capacity fan in front of grill to keep hi side temp/press down due to low airflow at idle or hit the condenser with a water hose briefly.
Depends on temp and humidity where your at.

Hi side pressures in excess of 300 should be avoided. Extended idling will cause hi pressures.

Pancake style compressor I'm guessing three cans it should be cooling, add slowly and check temps often. Placing the can in a container of warm water will speed up transfer of freon into system if needed
Click to expand...

Just checking here, so if the R12 is 3.25lbs then I only need to add roughly 80% of that for R134?
 
I could have sworn those measurements were when you were doing a simple conversion of freon only, without replacing the condenser due to the fact the r-12 condensers don't cool as efficiently as 134a units do.
 
80% is a base line, adjust according to best outlet temps, there is no exact measurement when converting, 134 operates at a higher pressure and requires less.
It's not as efficient as r12 in an older
system.
 
Justin Fleming said:
So I only got about 1.5 pounds in system through the low side. Just to be clear I did not ever open the high side when filling. At one point I did have the 134 vavle shut off and I did open both manafold valves red/blue just to see what was going on. When doing this did I introduce a bunch of the pressure to the low side by doing this? Should I drain the system down and start over?
Click to expand...
Don't take all the refrigerant out unless you're sure you need to open the system. It sounds like you might need to add. Are you getting any cooling? Is the line cold right after the orifice tube? How about the outlet line from the evap? As stated above, the weight of R134 in your R12 system is an approximation. The final judge is the outlet temp, not the weight. If you have 8/125, how quickly do they equalize after the compressor stops?
 
Blue85 said:
Don't take all the refrigerant out unless you're sure you need to open the system. It sounds like you might need to add. Are you getting any cooling? Is the line cold right after the orifice tube? How about the outlet line from the evap? As stated above, the weight of R134 in your R12 system is an approximation. The final judge is the outlet temp, not the weight. If you have 8/125, how quickly do they equalize after the compressor stops?
Click to expand...

as I seem to remeber they equalize realitivly quickly...
 
Some systems might need 90% of the charge of R12. 1.5 pounds is definitely too low. Be careful about bypassing the compressor switch, you can damage the system if you keep it running with low pressure.

Hopefully it works out. I'm looking to set up my A/C in a couple weeks, going to give the Envirocool substitute refrigerant a try.
 
SO I have roughly 3lbs of R134 in the system, the clutch is cycling what a would call normal. when clutch is engage and running the low side will drop to about 24lbs and the high side only gets to 175 and I only seem to get the vent temp down to around 45. I would have thought I could have gotten it colder and I also thought the high side should be much higher?

What are your thoughts....

thanks
 
That might be all you get out of it.

Also, there is no expansion valve in these trucks. They use an orifice tube.

Martin
 
Justin Fleming said:
SO I have roughly 3lbs of R134 in the system, the clutch is cycling what a would call normal. when clutch is engage and running the low side will drop to about 24lbs and the high side only gets to 175 and I only seem to get the vent temp down to around 45. I would have thought I could have gotten it colder and I also thought the high side should be much higher?

What are your thoughts....

thanks
Click to expand...

Is that on recirc or flow-through? What's the ambient temp?
 
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