AC help

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#1
2004 Chevrolet trailblazer LS
4.2 engine

I replaced fan clutch and the only way to make the ac work is to jump the relay and it cools fine. I also bypassed the low pressure switch and did nothing. What am I missing
 
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#2
STOP jumping switches! It may not be the low pressure switch*, and computers do not like elec shorts.

Scan for codes - yes even if CEL/SES is off. Some codes will have PCM restrict AC operation.

Do you have gauges low and high pressure? The 'transducer'* will need to see a minimum/max static refrigerant pressure to permit AC operation.

I suggest you check for codes first.

let us know manual HVAC or AUTOMATIC HVAC....
 

billr

wrench
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#3
Did the A/C work OK just before the fan clutch replacement? To me, a "fan clutch" is a viscous drive between the water pump and radiator fan; a purely mechanical device. Is that what you are referring to?
 
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#4
Did the A/C work OK just before the fan clutch replacement? To me, a "fan clutch" is a viscous drive between the water pump and radiator fan; a purely mechanical device. Is that what you are referring to?
NO it did not but the fan was spinning very slowly and I was told it had a speed sensor that may have something to do with compressor kicking on.

LIke I said if I jump the relay it blows really cold.
 
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#5
STOP jumping switches! It may not be the low pressure switch*, and computers do not like elec shorts.

Scan for codes - yes even if CEL/SES is off. Some codes will have PCM restrict AC operation.

Do you have gauges low and high pressure? The 'transducer'* will need to see a minimum/max static refrigerant pressure to permit AC operation.

I suggest you check for codes first.

let us know manual HVAC or AUTOMATIC HVAC....
THe codes said to replace fan clutch.

I did discover hot air blowing out of the passenger side vents

45 low pressure and 200 high pressure and that show right base on ambient temp
 
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#6
OK we will help get it fixed let us know the code P0xxx?

FYI or TMI-
Jumping the relay removes all sensors and modules from system operation, an easy test but not much more. Yes there is a Hall effect 'sensor' reading fan speed which is controlled by the PCM.
If the fan speed is lower than the PCM requests a fan code would set and PCM would restrict AC - logic would be - there is a cooling problem so why add to workload...
The code is the first step here.

A money saving tip - there is NO code that says replace a part.
 
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#8
have you tried a different relay? swap a like relay for testing....
 
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#11
THen we are back to codes post ALL codes.


Other ideas
Do you have a scanner - live data, bi directional capabilities?
Any recent work modifications or added devices?