AC pressures equal hi and low with LC running and compressor loaded?? (1 Viewer)

[jerryb]

I'm trying to figure out why the high and low side pressures are equal with the car idling and the compressor running/loaded. It reads around 110 psi.

I'm checking because the rear AC is blowing ambient and the front is cool, 49F or so. The front use to blow around 39F.

The high side fitting and hose gets really hot. Suction side is cooler than ambient.
The compressor seems to be loading but it might sound different than it use to. I think it's clicking more than in the past, but not sure.
I'm really a novice about AC, but I have a gauge tree and FSM. I didn't find any info about equal pressures.
Thanks for any help?

 

[TXSunDevil]

Equal pressures means the compressor is not compressing the refrigerant so it is probably not running. This is confusing because you are getting 49 degree air out of the vent.

 

[Julian Stead]

Got to agree, Compressor not working. What is the pressure and vent temp when air con is switched off?

 

[jerryb]

*with air con off pressures are the same., But I think it loads when I push the AC button*
It's hard to tell if it's engaged because it sounds different than it use to, but it must be if the front AC actually works.
i"m still working on it until the sun goes down.

To me it's confusing because I think the rear AC use to work fine. I was told it did by passengers but never checked. Front was always 39F with IR gun, until lately on a 650 mile trip, AC quit but worked well after leaving it off for 15 minutes or after a fuel stop. So then I started checking temps. That was a week ago with 95F ambient. Now it's 80F outside with 49-51F vent temps today while checking. Vent temp has been going up for a week, as well at the ambient outside temp going down (95 to 80 today)
I was thinking maybe something electrical, off chance. But probably compressor. Tomorrow I'm going to go through the motions on fsm. I just don't want to waste time if I need a new compressor. it will take me most of tomorrow to go through all the checks.

 

[Julian Stead]

Got to ask, have you got the correct refrigerant in the system.

 

[Julian Stead]

Ps, You should physically be able to see if the clutch is engaged, if it does engage then your pressure should get to the correct levels. So your main check is to see if the clutch engages, if not test why electrically, if it does engage then you would presume your electrics are good to a point and it is a pressure issue.

 

[jerryb]

Ok, So I might be an idiot.
When you check pressures are you suppose to have high and low connected, all valves open, and check pressures?
I understand now that of course they might/will equalise with a cheap/er manifold. I closed the high side and it would creep down a little and hold, and the low would settle down to .7 kg cm2 or around 10 psi, high side around 10 kg cm2 or 150 psi.
Then it seemed normal and I charged a 12 oz can and both came up to not quite book spec. Rear was starting to blow cold.
It's still under spec at the moment.
I guess I don't understand why AC valve blocks are open and communicate. Seems like there should be a block or a valve between the HP and fill ports.

Am I crazy or is the above procedure correct?

 

[Nostradamus]

IIRC the manifold gauge knobs should be closed (all the way clockwise) and connected to the high and low ports. In this configuration, the pressures in the AC circuit will be shown on the respective gauges themselves, as the closed position closes off the passage to middle chamber of the manifold where vacuum pump or refrigerant source are connected - not to the ports. So basically if you just attach the hoses to the ports and tighten the knobs clockwise and start the car/ AC (assuming the clutch is engaged) you'll see the actual high and low side pressures.

To add refrigerant, connect the supply thru the middle manifold port and slowly open the low side valve knob to draw the refrigerant gas into the suction side of the compressor. At that point, your low side pressure reading will be a mix of the low side circuit plus the refrigerant source container. Close it again to get the true low side reading, but it won't be off by too much.

If your compressor clutch doesn't engage, it can be because the low side pressure switch is keeping the compressor from running in a low refrigerant condition to protect it from damage. YOu can jump the clutch to + on the batter with a wire and if the clutch is working correctly, you'll hear it clunk into the engaged position. Easy to hear w the truck off.

Fire up the truck, jump the clutch to start the compressor running and check your gauges. Add refrigerant until you get pressure readings from the refrigerant table for your ambient temperature at the time of servicing.

Hope that helps.

 

[jerryb]

thank you for the input. I got a handle on it now. It took me a bit to understand the manifold. As always I posted too soon.
I was in panic mode. I definitely have a leak though, I charged two 12 ounce cans and one ounce or red dye. Pressures were reading 30psi lp side and 190psi or so hp side. Front and rear cold vent temps, front @ <40f and rear at 50f or so. It was getting dark, I shut it down. It's good to see the pressure switches working on the gauges.
thanks for your alls help

 

[Nostradamus]

thank you for the input. I got a handle on it now. It took me a bit to understand the manifold. As always I posted too soon.
I was in panic mode. I definitely have a leak though, I charged two 12 ounce cans and one ounce or red dye. Pressures were reading 30psi lp side and 190psi or so hp side. Front and rear cold vent temps, front @ <40f and rear at 50f or so. It was getting dark, I shut it down. It's good to see the pressure switches working on the gauges.
thanks for your alls help

those pressures look reasonable. I get about 35 degree vent temps on my FJ60 w aftermarket compressor and running R-134A