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A/C Low Output Issue

1K views 11 replies 4 participants last post by  CT090 
#1 ·
This one has me puzzled...

"04 Discovery- came to me with a bad evap core. I ordered an aftermarket core and since I was in there, also put an expansion valve in it. Did a full evac twice with our year-old Snapon AC machine, then filled it with the specified amount of coolant.

Since it was on the cool side when i did it, it was hard to determine at the time, but now that the truck is in Florida, it's apparent that it's not putting out enough cold air.

The system has a full charge and everything appears to be working, but it cools poorly.

What should I be looking for?
 
#2 ·
What does the condenser look like? Has it been beaten flat? Good air flow over it? The fan works?
If it's showing a full charge and no other apparent damage...well, is the compressor good? That's all I have.
 
#3 ·
Make surre that it's not accidentally set on ECON mode cos then the compressor is disabled, check fuse F6 and relay R11(swap it with R12/front fogs for test)... if all these are OK the dual pressure switch must be ruled out as well, unplug it and bridge the pins in the plug(it's the one in the top of the drier behind the grill)
 
#4 ·
First thing I would check would be the electric booster fan which is common to fail.
assuming that the low side pressure is decent (I would expect 30-35 psi with the a/c on)
it is quite likely that either it is not transferring enough heat (booster fan or the above mentioned condition of the condenser. Both will likely be indicated by excessively high - high side pressure

Is this a front or front and rear system? ( Different system refrigerant capacity)
If you can record static pressure , ambient temperature, high and low side pressures we will definatately have more to go on to try to help you.
 
#5 ·
Compressor works and the pressures are good. Mid 30's on the low side. Filled to the exact ounce.

It's front air only.

Condenser is in great shape and the fan is new. Has the problem whether idling or on the highway. Outside temp is only mid/high-70's.

I thought maybe an air door might not be operating properly or completely but I don't know what normal operation is. I thought maybe an airflow restriction of some sort could be an issue and causing evap frosting but I'm seeing condensation drain underneath.
 
#8 ·
From the RAVE:
When the engine is running, coolant is constantly circulated through the heater matrix by the engine
coolant pump.

So it does sound like the air doors (control flaps) aren't closing. There's a tiny chance the temperature sensor is bad, but I'd go with Occam's Razor and look at the simple things first. Check those air flow doors.
 
#10 ·
The air conditioning/heater temp sensor. It compares what the interior temp is compared with what you have dialed up on the control and either opens or closes the air doors to adjust. I'd hope the system would detect a fault, but since it's not an engine or transmission sensor, it's not high priority and might not be monitored.
 
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