Mikes94lt1

Hello I'm at a loss as to what the problem could be. I replaced my ac compressor about two weeks ago because the pulley was making a god awful noise. I replaced the dryer also.ran a vacuum on the system for an hour and it had no leaks.it worked good until I noticed the compressor cycling on and off about every ten seconds but still cooling.it showed a low low side so I added more and then it cycled about every second and was not cooling so I let some out and it worked great again.now it works good at random times.sat morning it worked awesome then the afternoon it stopped.i tested it last night and the compressor turned on and it had about 25 on the low side one ac line was cold other was hot and it was working good.now this afternoon it's back to cycling every second and not cooling. I keep thinking maybe it's leaking but the vacuum indicated there was no leak. Unless I just have the wrong amount In there it says 2 pounds and I put 36 ozs.i just need some options before I keep goin

Mikes94lt1

It will prolly help..it's a 94 z28

LinkinZ28

Hey Mike. I haven't had to much experience with my AC system on the lt1 yet, but I can offer some general advice. If you have R134a system as I'm pretty sure you do there should be an "orifice tube" somewhere. If not, an expansion valve. When compressors go bad internally they are notorious for contaminating the system, especially in the more confined passages. The orifice tube should have been replaced with the compressor, if not I would definitely start by replacing that, they are only about 5 bucks at your local parts store. Then obviously vacuum it back down and see if there is any improvement, if not drain it again and get a can of "AC flush" fluid, disconnect the two lines from the condenser (also has very small passages) and blow through it from side to side to remove any restrictions. It sounds 100 percent like you have a restriction in the system somewhere. Make sure there is plenty of oil circulating in there too!!

parkers Z28

Could the low/high pressure sensor be malfunctioning ?? giving false readings

Injuneer

The 94 system uses a thermostatic expansion valve.

Mikes94lt1

Ok last night I left work at 11 and it worked perfect freezing cold clutch engaged normally.however I did notice that the passenger side fan came on but the driver side fan kept coming on randomly and the voltage gauge was in the red,is this normal operation of the fans or no.Then I went out at 9 in the morning and it worked ok not the best but compressor wasn't cycling fast..I left for work at 2 and it was working for about ten minutes then started cycling very fast and was not working.When I get a chance I'll hook the gauges up to see what is happening when it acts up


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Injuneer

Details of fan operation depend on whether you have an "early production" 94 or a "late production. Early models have two relays controlling the two fans. The first fan goes on with the A.C. If the A/C isn't on, the first fan comes on when the coolant reaches 226*F. The second fan comes on when the coolant reaches 235*f.

For late production, the two fans are controlled by three relays, that operate them together - both fans on "low" speed with the A/C, or above 226*F, both fans on "high" speed at 236*F.

If your system voltage dropped into the red zone on the voltage gauge, it's possible the PCM cut off the A/C.... not sure if that feature is programmed in, but it may be. What would you estimate the voltage to be when it was "in the red"? What was the coolant temp when the second fan was coming on?

Mikes94lt1

I believe I have the early fan setup I only have two relays ..when the second fan comes on it's not even halfway on the temp gauge so not even 210 degrees.id say the voltage was like 10 Volts.however I never notice a fan come on when it reaches halfway with no ac on only when it reaches 235 almost at the red.maybe I have a cooling issue but the car has never overheated or that fan is really quiet..I'll have time tomorrow to do more digging around on it.i know for sure I need a alternator though


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Injuneer

The PCM sets codes for the fan control relay circuits.

The dash coolant temp gauge is fed by a 1-wire sensor in the driver side head. The PCM is fed by a 2-wire sensor in the water pump. It's possible the the temperature sensors do not agree.

Mikes94lt1

Ok of course I get time to check and it decides to work..however the passenger side fan never came on just the driver side..I put the ac on and both fans came on and stayed on with the ac working good.could be two separate issues but idk.with both fans running car never went halfway on gauge .how do I test the coolant sensors


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Injuneer

Shoebox has the answer:

4th Gen LT1 F-body Tech Articles

A real-time scanner, or scan software would allow you to see what the coolant temp sensor in the water pump housing is reporting to the PCM.