Automotive Air Conditioning Information Forum (Archives)

backtobasics on Thu June 13, 2013 12:43 PM

Year: 1995
Make: Ford
Model: Taurus
Engine Size: 3.0
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: 140
Pressure High: 125

Cliff's Notes:
Service side of auto dealership.

Taurus came from auction. Our normal service work was done, and vehicle inspection. A/C was trying, but not cold, but at same time noticed the engine cooling fan was inoperable.
Replaced motor to fan, now fan working perfectly.

I can't explain the readings right now. I will go on record now that I am using a basic set of Harbor Freight gauges, and filling via cans. Currnently working out of a garage while the shop is being built. We will move to the 30lb cans and scale once we get running in the full shop, but for now, we have been running with an approximate target of 45 low and 200 high. Not ideal, but it's what I have to do for the next month or so.

Right now, when compressor kicks on, it is 125 on high side, and low side is pegged, appear to be around 140. Low side gauge max is 120, and it is wrapped past. Air is "sorta cool" right now, with compressor kicking on and off, every 30 seconds.

Car is literally "grandma clean" with 129K miles and absolutely pristine.

94RX-7 on Fri June 14, 2013 12:48 PM

Detach and reattach the low side service hose while the compressor is running. I bet your reading will go down. Sounds like the coupler isn't depressing the valve core in the low side service port all the way except when you're pushing down on the connector to attach it.

mk378 on Fri June 14, 2013 5:18 PM

I agree, it must be a measurement error. You can't get any cooling at all if the low side really is 140.

wptski on Fri June 14, 2013 7:07 PM

Quote
Originally posted by: 94RX-7
Detach and reattach the low side service hose while the compressor is running. I bet your reading will go down. Sounds like the coupler isn't depressing the valve core in the low side service port all the way except when you're pushing down on the connector to attach it.
Your suggesting that that the low side pressure is really much lower, if so explain how a partially depress valve would make it show much higher?

mk378 on Fri June 14, 2013 7:38 PM

Assuming that you connected the hose before starting the compressor, the low side pressure was higher then. That high pressure is then trapped in the hose.

wptski on Fri June 14, 2013 7:48 PM

Quote
Originally posted by: mk378
Assuming that you connected the hose before starting the compressor, the low side pressure was higher then. That high pressure is then trapped in the hose.
If the connection is good enough to show the high pressure before the compressor runs then it's good enough to show the lower pressure after it's running. It can't be trapped, if it can get in, it can get out.


Edited: Fri June 14, 2013 at 7:48 PM by wptski

mk378 on Fri June 14, 2013 8:05 PM

Read what 94rx-7 said again.

Or go out to the car and press the connector down onto the port while the system is running and see if the pressure changes.

Also on used cars of unknown origin, there is always the sceptre of stop-leak.

wptski on Fri June 14, 2013 11:06 PM

Quote
Originally posted by: mk378
Read what 94rx-7 said again.



Or go out to the car and press the connector down onto the port while the system is running and see if the pressure changes.



Also on used cars of unknown origin, there is always the sceptre of stop-leak.
I replied to his post but you replied to mine.

The gauge would be at zero and go up when connect. What does that prove? Actually that would depend on your adapters, if they depress the vavle core when connect or you have the type with a manual depression knob. A partially depress valve core is just that, neither fully closed nor fully open. Restricted flow at most.

I'm no AC Tech but I sure don't get your explaination. Although I have a R134A adapter kit, I've never worked on anything but R12 systems so far. Maybe I'm missing something.

94RX-7 on Sat June 15, 2013 8:26 AM

Quote
Originally posted by: wptski

If the connection is good enough to show the high pressure before the compressor runs then it's good enough to show the lower pressure after it's running. It can't be trapped, if it can get in, it can get out.

With this type of R-134a quick disconnect connector what happens is you push the connector down onto the service port, it "clicks" in place, then it rises back up a bit before the locking mechanism "grabs" the service port preventing further movement.

What I suspect might be happening in your case is that extra travel downward as it clicks in place is enough to depress the valve core and allow refrigerant to pass through. Then it rises back up a bit to the locked position, and that's just enough rise to not depress the valve core. I've had it happen on several occasions. Sometimes detaching and re-attaching works, other times I have to get a different hose/connector.

wptski on Sat June 15, 2013 8:43 AM

Quote
Originally posted by: 94RX-7

With this type of R-134a quick disconnect connector what happens is you push the connector down onto the service port, it "clicks" in place, then it rises back up a bit before the locking mechanism "grabs" the service port preventing further movement.



What I suspect might be happening in your case is that extra travel downward as it clicks in place is enough to depress the valve core and allow refrigerant to pass through. Then it rises back up a bit to the locked position, and that's just enough rise to not depress the valve core. I've had it happen on several occasions. Sometimes detaching and re-attaching works, other times I have to get a different hose/connector.
I'm not the OP but questioned your reply.

Okay I understand what your saying now! Sounds like it's better to have the type of adapter with the manual knob to depress the valve core to avoid this problem?



Edited: Sat June 15, 2013 at 8:44 AM by wptski

94RX-7 on Sat June 15, 2013 9:44 AM

Quote
Originally posted by: wptski

Okay I understand what your saying now! Sounds like it's better to have the type of adapter with the manual knob to depress the valve core to avoid this problem?

I've seen those, but I've never used them. If they allow for a great enough range of adjust-ability then they probably can side-step this problem.

wptski on Sat June 15, 2013 10:13 AM

Quote
Originally posted by: 94RX-7
Quote
Originally posted by: wptski


Okay I understand what your saying now! Sounds like it's better to have the type of adapter with the manual knob to depress the valve core to avoid this problem?



I've seen those, but I've never used them. If they allow for a great enough range of adjust-ability then they probably can side-step this problem.
I believe they about $10 more for the set than the others.