Gentlemen:

My air blows cold on startup, but only for about 5 minutes, then it seems to blow ambient air temperature. If the truck sits for a period of time, once again I get my 5 minutes of cool. Could low refrigerant levels do this? I wonder if it might be electrical, i.e. clutch related?

'97 scab 4.6l, 265k kms

TIA

Dan

 

Check how much your clutch is engaging, like on/off every 5 seconds. If so, you'll probably only need a top up.

 

On a cold start, open the hood and watch the compressor clutch for the five minutes that you indicates it takes to fail to see if the clutch disengages and does not re-engage.

Since the system cools properly initially, it may not be a low refrigerant issue. I'd rather suspect one of the following: Clutch slipping, inadequate heat rejection from condenser due to a fan/radiator airflow problem, or the evaporator may be icing.

Steve

 

Forgot one test, get truck up to operating temp, open all doors and turn on a/c full speed. There are 2 tubes, aluminum coming from the firewall into the evaporator. If at this time there is a big temp difference, like one is ice cold and the other is room temp, low refrigerant. There should be only a 10 degree diff. If all is good, move on like projectsho89 describes. He seems pretty good at this HVAC crap.

 

Gents:

Thanks for your input. I cold started the truck yesterday. When air is turned on, the clutch engages and disengages as you mentioned it should, and did so for a good 10min while sitting, then I went for a drive, after about 5min, I could feel the air start to get warm, I looked and the clutch was no longer engaging. So it would seem that it is possibly alright as far as refrigerant levels go??
I take it that the evaporator is the aluminum, can shaped unit under the hood, and the condensor is the rad type unit in front of the engine radiator? No apparent blockage to air flow on the rad type unit, and can't tell if the evaporator is freezing.
Shut the truck off after this test and went out more than an hour later, and it still wouldn't engage the clutch. What sensor turns the clutch on and off? If it is the GEM, I wonder if that is the problem, I have a few potential GEM glitches ( mainly wiper related )and wonder if it might affect the AC?

I can't think of any more backyard diagnostics I can do, or test procedures to carry out for now.

TIA

Dan

 

Does sound low on refrigerant, so maybe take it to a shop, get a full inspection (charged for it anyways even if it's an obvious prob) and see what's up. Nine times out of ten it's low, but the sensor may be deep sixed. Your compressor will kick on and off alot to keep from burning out, and after a while, it's probably not able to kick on at all. After mine was topped up, the compressor for the most part stays engaged and now blows friged cold. You could have a .25 cent o-ring gone too if a leak is detected.

 

The evap is in the dash.

The "can" is the accumulator or receiver/dryer.

The GEM module is not part of the A/C clutch circuit.

You do not have any symptoms of low refrigerent. Those usually include clutch short cycling or poor performance.

You have good performance followed by NO performance.

I'd suspect a worn clutch (excessive air gap) or an electrical intermittent (connector, wire, or cycling switch).

Check for battery power at the BLACK/VIOLET clutch connector with a meter the next time it fails (should be engaged but is not). If power is there, the clutch is the problem.

If no power, remove the connector from the cycling switch (on the accumulator) and briefly jumper the connector. If the clutch engages, the cycling switch is not closing and may be defective.

Steve

 

Gents:

Thanks once again for input. I was under the impression that the clutch was supposed to cycle on and off, but apparently that is not correct. I timed it, it was staying on for about 12-14secs, and of for about 6-8 secs, after a while it just stayed off. So, does this help your diagnosis?

Thanks, Dan

 

Yes.

Now, follow the last two steps in my previous post.

And/Or

Just tap the clutch with a broomstick or rubber mallet when it stops staying engaged to see if the physical shock causes it to pull in. If so, the gap is too great or the coil is weak.

Steve