2nd Gen Non-Engine/Transmission Air Conditioning Pressures

[ceastmen]

Now that summer is almost here in the Rocky Mountains I fired up the A/C in my truck. It would cool down some but not like it had in the past.

I added 1 can of R134a it helped but the compressor would not cycle on and off, just ran all the time. I put gages on the high and low sides, 35 psi low side and 175 psi high side, while on max air and fan on high. Now here is where it acts up, I had my wife turn the A/C off and watched the pressures, the high would start to drop down to 75 psi while the low would climb up to 75 psi as if they were equalizing, is this normal?

If I would wait for a minute or so and have my wife turn the A/C back on, I would hear a shudder comming from the high pressure hose and notice a vapor spray comming from the back of the compressor.

I probably need a new compressor but wanted to ask the menbers on TDR if these are symptoms of a bad compressor before I spend the bucks for one.

Thanks in advance

Chuck

 

[JJPage]

All refrigerant systems equalize pressure at rest, that is normal. Visible spray from the back of the compressor is not normal, but at least you know where it's leaking.

 

[B.G. Smith]

Sounds like you overcharged the system and liquid is getting to the compressor. What you are seeing is the high pressure relief valve releasing when the compressor comes on. If you get proper amount of refrigerant in system compressor may or may not be ok????? bg

 

[B.G. Smith]

[

(I added 1 can of R134a it helped but the compressor would not cycle on and off, just ran all the time. I put gages on the high and low sides, 35 psi low side and 175 psi high side, while on max air and fan on high. Now here is where it acts up, I had my wife turn the A/C off and watched the pressures, the high would start to drop down to 75 psi while the low would climb up to 75 psi as if they were equalizing, is this normal?)

The temperature of R-134 at 75# pressure is about 73 degrees F. So if the outside temperature was in low 70s and the compressor was cycling then the charge was probably pretty near correct before you added the can. The system full charge is somwhere around 32 ounces. bg

 

[budnate]

Sounds like you overcharged the system and liquid is getting to the compressor. What you are seeing is the high pressure relief valve releasing when the compressor comes on. If you get proper amount of refrigerant in system compressor may or may not be ok????? bg

x2... pull the fuse on the a/c until you bleed some off or you will be buying a new comp, you are hammering the system hard... ... pay close attention to outside air temp and system pressures when charging!.

 

[JJPage]

Sounds like you overcharged the system and liquid is getting to the compressor. What you are seeing is the high pressure relief valve releasing when the compressor comes on. If you get proper amount of refrigerant in system compressor may or may not be ok????? bg

B. G. I am not very familiar with automotive refrigerant systems, I maintained and installed commercial HVAC systems for 10 years for telecommunications industry. I have never came across a high pressure relief/release valve(on hvac) that would reseal/close after once letting loose. Do our trucks compressors actually have that feature?

I could understand the possibility, we have a relief valve on our rail that operates at a higher pressure than the AC system. The only high pressure release component I've seen on an HVAC system, was like a little solder plug that let loose if pressures became too high, but those just blew and you lost all refrigerant. The high pressure safeties would open the control circuit to shutdown the system to keep within safe limits or liquid from slugging the compressor, but did not leak off any refrigerant. And as you stated above, that sounds like what happened with the OP. I am going to go out and look at my compressor, see if I can spot this valve.

Learn something new everyday, Jess

 

[B.G. Smith]

It appears that these do have one, it is located on the bottom of compressor near the rear. I have seen them over the years but haven't done any compressor change out in a while. I am suspecting that the compressor they are using now may be rotary vane and can stand some abuse where the old ones with pistons and reed valves woud wreck when slugged. One reason I say that is we have a 05 Mercury and if it has been setting overnight and the temps are cold the first engagement of the compressor chirps the belt, fine the rest of the day. Refrigerants are known to migrate to the lowest spot in a system when out of operation and it seems that almost all the compressors are now on the bottom of the engine. Also if the compressors are vane type that would account for the quick equilization of pressures after shut off. bg

 

[ceastmen]

High pressure releif valve

BG & budnate

I beleive your right about the High pressure releif valve, my system has not lost any pressure. Do you know how to releive some of the pressure (R134a), I read budnates post about pulling the fuse to do this, could you go into some more detail on how to do this, sorry for being lost on this end.

Thanks,

Chuck

 

[B.G. Smith]

You will need to hook up a charging hose to the low pressure line and open the valve slightly on the gages to slowly let the gas out, if you let it out too fast the refrigerant and oil will boil and some oil will be carried out with the gas. Engine does not need to be running. Just do it slowly. After you have let out some refrigerant, start truck and turn system on, if you have a hand held pyrometer you might be able to check the temp of the condenser in front of radiator and see where the liquid level is, probably chould be up about 4 or 5 rows of horizontal tube with AC running. Temp of condenser will drop off above the liquid level. bg

 

[budnate]

You will need to hook up a charging hose to the low pressure line and open the valve slightly on the gages to slowly let the gas out, if you let it out too fast the refrigerant and oil will boil and some oil will be carried out with the gas. Engine does not need to be running. Just do it slowly. After you have let out some refrigerant, start truck and turn system on, if you have a hand held pyrometer you might be able to check the temp of the condenser in front of radiator and see where the liquid level is, probably chould be up about 4 or 5 rows of horizontal tube with AC running. Temp of condenser will drop off above the liquid level. bg

x2 again, only reason I said pull the fuse was to disable the comp from trying to work while you ran the truck until you bled off some gas, the comp pop off will reset on these units, if you worked on a/c gear you know what your doing, just watch the OSA temp mild temp days are a real pain to charge a system right, it wont stay loaded long.



your used to a data center throwing a constant load at your gear and getting it dialed is easier.