On a 2007 Chevy Express 3500 with 4.8 the condenser fan doesn't turn on when the ac is turned on. Is the fan on this model only supposed to start when high pressure side reaches 300 psi? I was told it should switch on low speed when the ac is first turned on, someone else said that vehicle didin't come with a fan, but it looks factory to me. I tested with other power source to the fan and it runs fine & fuse is good.

 

does it have both fan clutch and electric fan?
if only electric...its should come on full when the ac is engaged. if it didn't, the high side pressure would trip the high pressure switch in 30 to 60seconds of operation.
Does the a/c clutch compressor engage?

 

Yes, it has both. Maybe my high pressure switch is bad, but no idea where its located. (just purchased this vehicle with very low miles that hadn't been driven much.) The ac compressor engages, does not cycle on/off and the high & low pressures are 250 / 52. Could I just run the fan's hot wire to a power source that switches on when ignition is on with other wire to ground? I assume fan speed would change if the ecm sent different voltages (not sure if this one does) and if its a problem to run the fan constantly with a manual switch to turn off in colder months? I also heard about connecting the fan directly to the compressor relay, but don't know where that is or if current draw is a problem.

 

the clutch will only cycle off for set criteria:

• Throttle position is 100 percent
• The A/C compressor cycling switch pressure is less than 124 kPa (18 psi) or more than 338 kPa (49 psi)
• The A/C high pressure cutout switch is more than 2896 kPa (420 psi)
• Engine coolant temperature (ECT) is more than 123°C (253°F)
• Engine speed is more than 5000 RPM
• Transmission shift
• PCM detects excessive torque load
• PCM detects insufficient idle quality
• PCM detects a hard launch condition

I could not find and electric cooling fan information in the fsm for this build. is the 10th vin character a 7?

 

Yes, the 10th character is a 7. This was a former govt. vehicle that has a 2nd ac/heat system mounted on the floor behind the front seats. Its possible this fan was put in with the second ac but that rear ac system has since been disconnected. Today a new problem started - after I adjusted the temp dial slightly warmer then put it back to coldest, air from vent is cold for 15 seconds then no cold air for 15 sec. back & forth but only at speeds above 60 mph. I don't hear the compressor cycling on/off at idle and just 2 days ago my pressures were good so I assume I'm not low on freon.

 

Not sure where my post went from a few days ago, but I have new info now. Yes, the 10th character is a 7. This cargo van was former Govt with a custom rear AC/Heater mounted behind the bulkhead & I was told by someone the condenser fan was most likely put in at the same time. Before it was sold many wires were cut including the rear ac system so I assume the fan is also disconnected. Could I run the fan wire to the compressor relay with an inline relay so it runs every time the ac comes on? Also the ac is cycling on/off every 10-12 seconds but only at speeds above 60 mph! With pressures at 50 low side / 250 high I don't know why it would behave this way.

 

Lots of newer vehicles don't even use an A/C high-pressure switch. There is a plug with a C-clamp on the back of my 98 Chevy K-1500 A/C compressor where one could be placed, as I have seen some older models use it, but my guess is that you don't have one either.

 

When I initially posted the compressor wasn't cycling at any rpm/speed, but after I turned the temp dial slightly toward red then half hour later back to max blue for coldest, the compressor has been cycling at speeds 60 mph every since.

 

I like hearing good news. Congratulations on your A/C system working properly!

One of many tricks I use to prolong the life of a vehicle is to use every system, needed or not.

For instance in the hot summer, I turn the heater on full blast with the cabin recirculation system going for half an hour or so. I figure two things:

.1 The heater core is flushed out real good with newer coolant.

.2 The Cabin air-recycle system works, even if I never use it.

My 98' Chevy K-1500 is a 5-speed manual transmission. Everything is stock. I keep in neutral at long stop lights to save the throw-out bearing from an early demise. So far it works well.

Let us know if your A/C gives you any more problems, MX3500

 

Sorry i wasn't more clear - I was posting about a new problem. The condensor fan issue is resolved but after I turned the temp dial slightly toward red then back to max blue 30 minutes later, the compressor has been cycling on & off but only at speeds above 60 mph. In other words what I'm implying is by moving the temp dial while the a/c was on might have caused the mixer door to move back and forth at higher rpm causing the air vent temp to alternate cold air on/off as if the compressor is cycling on/off. Alternatively, the compressor is coming on/off only at speeds above 60 mph.