KySilverado

iTrader: (7)

Guys, Really need some help. LONG description.... please bear with me.

My compressor went out about a month ago. Really haven't driven the truck since and the time I've tried not to have the A/C cycling. Even though it wouldn't cool the A/C clutch would cycle.

Went to a buddies shop today to fix it. Replaced the compressor (used low mile unit) orifice tube, and dryer. The orifice tube did have crud in it and verified the old compressor was screwed. Wouldn't suction or compress by hand turning. We flushed the lines and evaporator. I've read you can't really flush a condenser so we didn't try.

We used a reclamation unit. Vacuumed it down, it held for 5 minutes and put in the 1.6 lbs of R134A per the service manual. We also added back the amount of oil we drained out of the old compressor + another 2 ounces for the dryer. Per the GM service manual.

After the recharge we fired it back up and the A/C clutch would cycle for about a second after starting and then no more. It's a electronic controlled unit, tried it at its lowest setting and the defrost option. Tried jumping the low pressure switch on the dryer. No A/C clutch engagement ever, aside from the about a second at startup. I hooked up HPT, command the A/C clutch and it will work. Everytime. Appears to cool while commanding the compressor to run.

Had a GM buddy by for a bit and connected a GM Tech tool. Couldn't keep it long, it had to get back to work No stored A/C codes.

I can scan the I assume High pressure switch voltage with HPT It will read about .6v no compressor run and about 1.3v when its running so it appears to be okay.

WHAT else will keep the A/C clutch from engaging in one of these things??? Some research and I cam up with this from the web

"The powertrain control module needs to receive a bunch of correct data from switches (three pressure
switches under the hood), sensors and the HVAC control module before it will engage the A/C compressor.
The best diagnostic route for a technician would be to check all these inputs with a scan tool before
taking the next step."


HELP PLEASE !

AKlowriderZ71

iTrader: (22)

With the oriface tube plugged, sometimes it causes the pressure to spike in the system, and the high pressure cutoff switch turns off the compressor. Check the high pressure cutoff switch for debris and function. It might be 'stuck'.

03 BLACKOUTSSS

iTrader: (3)

my truck takes almost 3.0lbs of freon in stock trim. from my days as an AC refrig tech, it sounds like you are running too low on freon. Too make it more confusing, you could also be running too high. believe it or not, you'll get the same symptoms from both problems, if the pressure is too high on the low side when it kicks on, the pressure will build past the safe limit, and the compressor will turn off (built in safety switch). If its too low, I don't know how it does it, but it turns itself off if the pressure isn't building fast enough. First I would verify that you have the proper amount of freon in there. Simply enough, add about a half a pound to the low side with the compressor turned ON. When running, I believe the low side should be running about 30 to 35 psi.

Hope this helps.

AKlowriderZ71

iTrader: (22)

I looked it up, and found the R134a capacity is 25.5 ounces, which equals 1.6 pounds. Also, the system requires 8.0 ounces of compressor oil. Unless Mitchell is wrong(could happen).

KySilverado

iTrader: (7)

Thanks for the input guys.

I'm confident in the refrigerant charge numbers 1.6 lbs and AK you are correct the total capacity of oil is 8oz.... completely empty. Since I didn't change out all the components and flush everything just needed to add back for what I replaced and flushed. About 4 oz total. Can't really gauge the charge until I get it cycling like it should and watch the pressure gauges during operation.

Don't think the high switch is stopped up since I can read it's output voltage with HPT and it is reading a range of .6v up to 1.6v. Low side of the ranges but more importantly its varying when I command the A/C clutch on, so shouldn't be stopped up. I priced this thing and its like $65 bucks or I'd just go ahead and replace it. Also if it has been tripped it appears it will throw a DTC. DTC P0530 - Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit

Did some more research and it appears the HVAC control module actually looks at the low pressure switch input. The pcm gets the high pressure switch input. Im going to pull the fuse on the HVAC module tomorrow and let it re-calibrate as it appears to be what actually controls the A/C clutch. Keeping my fingers crossed. If that doesn't do the trick I'm stuck.

Coban

iTrader: (14)

I had this same problem problem a few months ago. (orifice tube) There was crap in my orifice. It didn't even look like that much, but sure enough, I replaced it and everything worked fine after that.

My compressor would come on for less than a second then shut off. I could command on with hptuners too.

AKlowriderZ71

iTrader: (22)

Maybe some more debris has found its way into your new oriface tube, Roger. Simple to check.

KySilverado

iTrader: (7)

Thanks again for the thoughts guys.

I agree that a clogged orifice will cause the A/C not to cycle. No gas from the high pressure side could make it through the tube and hence no low or too low a pressure. The low pressure switch would then shut off the system. I've actually already swapped out the orifice tube twice. Immediately after replacing the compressor and again after commanding the compressor to run a bit, just to see if there was any more crud in the system. There was a small amount the second time, not enough to stop it up. I'm gonna keep replacing it till I find nothing to be safe. They're only a buck apiece.

Even with the low pressure switch jumpered the clutch will not engage without me commanding it. When I commanded the compressor I was seeing 60-75 psi on the low side. Should be enough to run the compressor?

AKlowriderZ71

iTrader: (22)

Yeah, I'm sure your problem isn't with low pressure, or the low pressure switch. I believe the problem is with a malfuntioning high pressure switch.

KySilverado

iTrader: (7)

Found this in the service manual. Don't think any of those conditions were happening. It was below 40 ambient outside the garage. Something like 59 in the garage.



The air conditioning (A/C) compressor clutch will not engage under the following conditions:

* The A/C high side line pressure is over 2957 kPa (429 psi).
* The A/C low side line pressure is under 138-172 kPa (20-25 psi).
* Throttle angle is at 100 percent.
* Engine speed is more than 5500 RPM.
* Engine coolant temperature (ECT) is more than 121°C (250°F).
* Ambient air temperature is less than 5°C (40°F).
* Engine is idling at a low unstable RPM