A/C not blowing cold, but pressures are fine

[DMC5180]

I would expect a plugged orifice to cause abnormally High side pressure. Unless the system is just very low on refrigerant.


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[David T]

One way to check what is going on is to remove and measure the amount of refrigerant. For the pressures to look correct and no cooling several things would have to be bad at the same time. Verify you are moving enough air over both coils. It is possible to have the correct high side pressure with low refrigerant if the condenser coil is not dissipating heat because of insufficient airflow due to bad fans or dirt blocking airflow. On the low side the evap coil could be freezing over.

[DMC-Ron]

One scenario that would explain the AC working but no cooling is the heating is stuck on and working simultaneously. Combination of evaporator cooling plus heating coil heat gives you warm air. You should be able to eliminate the heat by putting the mode switch to MAX. But that assumes your heat valve works. Observe and verify that the heating valve is closing when MAX is selected. Even if it looks like it's working, you could clamp the heater hose near the valve to close it off for testing.

Heater Valve sketch.JPG

If you find the heating coil is the culprit, you'll need to look into the heat flap to see why the cooling from your evaporator is going thru the heating coil. Normally this is regulated by your temperature control knob.
Ron

[Bitsyncmaster]

I would expect a plugged orifice to cause abnormally High side pressure. Unless the system is just very low on refrigerant.


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I would expect that also but since the compressor shuts off at 30 PSI on the low side that may not be the case.

[Project Vixen]

At present, I'm still leaning more towards some type of physical blockage in the airbox. First, I would believe it would be highly unusual for the compressor pressures, cycling, etc. to be perfectly in spec if there were problems in that part of the system. Second, my wife said she thought there might be a mouse nest in the box as she saw little puffs of lint keep flying out of the round air portals on the sides of the dash for the door air vents.

Some things I'm thinking I should try:

• test the a/c with the car cold. Then there's no interference from the heater core
• feel the accumulator/drier to see if it's getting cold.
• drop the blower fan and look for signs of blockage
• drop the bottom of the evaporator's housing
• check the hot water valve, just because it was the last thing replaced.

Thanks to all for the continued suggestions and help!

[Ron]

At present, I'm still leaning more towards some type of physical blockage in the airbox. First, I would believe it would be highly unusual for the compressor pressures, cycling, etc. to be perfectly in spec if there were problems in that part of the system. Second, my wife said she thought there might be a mouse nest in the box as she saw little puffs of lint keep flying out of the round air portals on the sides of the dash for the door air vents.

Some things I'm thinking I should try:

• test the a/c with the car cold. Then there's no interference from the heater core
• feel the accumulator/drier to see if it's getting cold.
• drop the blower fan and look for signs of blockage
• drop the bottom of the evaporator's housing
• check the hot water valve, just because it was the last thing replaced.!

Sounds like a diverter/duct problem to me too (if accumulator cold).

====

fwiw, a partially restricted orifice would make the high side go high and the low side go low. Blocked, the high side would go extremely high and the low side go negative (vacuum). Bypass LP Switch to test.
If those pressure readings were taken when the clutch cycled out, they are near perfect for that ambient temp.

[Project Vixen]

Ok, finally got a chance to look at a few things. I dropped the fan so I could feel around for any obstructions/mouse nests, but it was all very clean. The accumulator and evaporator both get cool -- but not cold -- when the a/c is on.

Some other things to note:

• tested from a cold start so there was no interference from the heater.
• the compressor's 'on' cycle is only 2-3 seconds, with around 60 seconds off
• the cooling fans don't come on when I turn the a/c to max. Aren't they supposed to stay on? I am running a Fanzilla so there is a delay before they kick on. I jumpered the fan at the otterstat and they ran fine.

Not sure what to check out next. Ron's suggestion of checking the pressure switches makes sense... Any thoughts? Thanks again, all, for the assistance!

[hippieman9]

Ok, finally got a chance to look at a few things. I dropped the fan so I could feel around for any obstructions/mouse nests, but it was all very clean. The accumulator and evaporator both get cool -- but not cold -- when the a/c is on.

Some other things to note:

• tested from a cold start so there was no interference from the heater.
• the compressor's 'on' cycle is only 2-3 seconds, with around 60 seconds off
• the cooling fans don't come on when I turn the a/c to max. Aren't they supposed to stay on? I am running a Fanzilla so there is a delay before they kick on. I jumpered the fan at the otterstat and they ran fine.

Not sure what to check out next. Ron's suggestion of checking the pressure switches makes sense... Any thoughts? Thanks again, all, for the assistance!

I believe the Fans should kick on on max. Set the switch to Max, and turn the ignition switch to run, without starting the car and see if the fans kick on. Also check and make sure the recirc door is opening on max and the Hot water valve is closed. I recently learned that they only operate on the Max setting.

[DMC5180]

Ok, finally got a chance to look at a few things. I dropped the fan so I could feel around for any obstructions/mouse nests, but it was all very clean. The accumulator and evaporator both get cool -- but not cold -- when the a/c is on.

Some other things to note:

• tested from a cold start so there was no interference from the heater.
• the compressor's 'on' cycle is only 2-3 seconds, with around 60 seconds off
• the cooling fans don't come on when I turn the a/c to max. Aren't they supposed to stay on? I am running a Fanzilla so there is a delay before they kick on. I jumpered the fan at the otterstat and they ran fine.

Not sure what to check out next. Ron's suggestion of checking the pressure switches makes sense... Any thoughts? Thanks again, all, for the assistance!

That cycle time seems way off. Usually the clutch would stay ON almost continuously at idle in hot conditions.
Can you post a video of your manifold gauges hooked up and A/C running?

[DMC-81]

Ok, finally got a chance to look at a few things. I dropped the fan so I could feel around for any obstructions/mouse nests, but it was all very clean. The accumulator and evaporator both get cool -- but not cold -- when the a/c is on.

Some other things to note:

• tested from a cold start so there was no interference from the heater.
• the compressor's 'on' cycle is only 2-3 seconds, with around 60 seconds off
• the cooling fans don't come on when I turn the a/c to max. Aren't they supposed to stay on? I am running a Fanzilla so there is a delay before they kick on. I jumpered the fan at the otterstat and they ran fine.

Not sure what to check out next. Ron's suggestion of checking the pressure switches makes sense... Any thoughts? Thanks again, all, for the assistance!

Hmm. I agree that a 2-3 second on cycle time and minimal cooling typically points to a low refrigerant condition. With a full charge of R-12, my compressor seems to stay on all the time in these summer temperatures. Ignoring any impact of the Fanzilla unit, yes, as mentioned, as soon as you click the Max mode on, the fans come on immediately and stay on.

I agree to check the pressure switches. I originally had similar problems with minimal cooling and after lots of troubleshooting my problem turned out to be an oil logged evaporator. Apparently this problem has degrees of severity, and mine was completely blocked so I had no pressure building.

Off topic, I just want to thank you for the great information on rebuilding the door lock solenoids. I was able to do the same thanks to your information.