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A/C Issues

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Old 07-11-2018, 05:31 PM
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A/C Issues

Hey guys I am seeking some insights. My ac wasn't blowing cold so, I replaced the compressor, accumulator, evap core, and valve. It did blew cold for a day then back to just air. I did have it evaced and recharged btw. So this is what is going on. When the truck sits overnight, and I go to drive, it blows cold. When I am in stop and go traffic, or the engine is at operating temp, the compressor kicks off, and I get just air. So where do I go from here? I am frustrated and not sure where to turn, I am thinking to replace the heater relay, or ac relay (not sure if their is one).
This is what I have replaced:
Compressor,
Accumulator
evaporator
valve,
fan clutch
vacuum hoses,
radiator
rad cap
thermostat
upper & lower hose (radiator)
(water pump, i have it, just did not install it)

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Old 07-11-2018, 05:52 PM
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What vehicle are you working on? What engine does it have?

Are there any leaks in the Air Conditioning system?

What type of refrigerant is in the system (R12, R134a, or converted from R12 to R134a)?

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Old 07-11-2018, 06:51 PM
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Sorry, 1991 pickup, V6 auto 3vze. It is converted over to the R-134, and as far as I know, there are no leaks. Firestone did the evac and recharge, and they said it wasn't leaking.
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Old 07-11-2018, 08:53 PM
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Automatic with 4wd (only) has an A/C Cutoff Relay http://web.archive.org/web/201102052.../2aircondi.pdf and an additional temp sensor to drive the relay. The relay itself hangs from the cooling unit.

If your temp sensor FOR THAT RELAY is out of spec it might be activating the relay at a too-low temperature. Or, your stop and go driving is bringing the coolant to the high temperature where the A/C is SUPPOSED to shut off.
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Old 07-11-2018, 09:01 PM
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My truck isn't a 4X4. 2WD. What would cause the compressor to shut down? Bad relay? Bad compressor, even though it's new from Oreilly Auto?
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Old 07-12-2018, 09:51 AM
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Quick update, my daughter took the truck this morning, she said the ac was blowing cold. So it seems the ac doesn’t blow cold throughout the startup and shut down of the engine throughout the day. When the engine is hot, i notice two things, not sure if their related. First is of course ac not blowing cold, and the other is, the engine seems to lose power/ doesn’t idle normally. I notice this at a stop light or when the car is parked. So cold start the ac is cold, idle normal, engine warm/hot, issues.
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Old 07-13-2018, 10:51 AM
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Hmmmm, not an AC tech, just another Toy owner trying to get by. I believe the compressor in these toys do not cycle? When you park after driving and the AC not working are you getting a big puddle of water on the ground under the passenger side by the firewall. When driving does the fan become louder and sound strained. I'm thinking maybe the condenser is freezing up??
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Old 07-13-2018, 10:55 AM
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No big puddle underneath. I thought the fan did sound a little loud, but I thought maybe it was the fan clutch, which I replaced. Sounds better now, but info notice the one going down, then it cause the compressor to shut off?
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Old 07-13-2018, 11:06 AM
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Originally Posted by jjrbus View Post
... I believe the compressor in these toys do not cycle? ...
Yes, they do. Controlled by the A/C Amplifier, which relies (mostly) on the dual pressure switch.

On a cool day, your thermal expansion valve (by the evaporator) lets through less refrigerant. The high-side pressure keeps building up, and the pressure switch calls for the compressor to stop. Once the TXV works the pressure down, the compressor restarts.

On a hotter day, more refrigerant through the TXV, the compressor is "on" more of the time.
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Old 07-13-2018, 11:11 AM
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Where is the AC amplifier located? Is there a way to test if it's bad? I'm in Phoenix so it's hot and the only time I see or feel a difference with the engine, is when it "idles down". When I say idle down, I am referring to the engine not running normal, feels like it's gonna die out. So. Have to do some checking this weekend.
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Old 07-13-2018, 11:52 AM
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Amplifier can be tested.
Attached Files
File Type: pdf
Amplifier.pdf (11.3 KB, 10 views)
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Old 07-13-2018, 12:27 PM
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The A/C amplifier is on top of the cooling unit (where the evaporator is).

There is no procedure for directly testing the Amplifier. The page provided by jjrbus is actually to test the HARNESS side of the connector to the A/C Amplifier. The manual suggests that if you get all the right voltages on the harness side, then you should replace the amplifier. That might be okay for a dealership, but you'll go broke pretty quickly putting in a new amplifier on a guess. (It's only $58-$75 depending on model, but still ...)

If you suspect the operation of the amplifier, and you have the knack, you might get further using the circuit diagram. http://web.archive.org/web/201102052.../2aircondi.pdf
You could, for instance, watch the output of the pressure switch, and see if that shuts off the compressor.
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