What went wrong?

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  #1  
Old 06-21-03, 06:31 PM
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Question What went wrong?

This is the reason I don't do auto a/c.

A friend dropped by to have me look at his '98 Caravan a/c with 180 k km. I don't do car a/c but I said I'd take a look.
Low suction and high head pressure with a bug coated condenser. While the vehicle and fan were running I sprayed the condenser off with a 600 psi washer and after I finished, my friend who was behind the wheel said that the a/c was blowing hot while in the max a/c position. I didn't spray a lot of water and it didn't even make it to the fan side. Then whenever the radiator fans cycled on the air came hot, fan off and it started to cool???
Of course it never did this before.
Also the air coming from the drivers side grills was warmer than pass side. I couldn't see any individual driver/pass comfort controls.

What gives?
 
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Old 06-21-03, 09:04 PM
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usually these have 2 fans are they both working cycling on and off?
the only difference that i would think you would of made by cleaning the condensor is lowered the high side pressure perhaps it is low on freon and now the high side pressure is to low or drops very rapidly when fans do kick on, the fans do cylce with high side pressure and do not usually come on till around 200 psi pressure reached, and usually on a hot day at idle with a full system the fans will run all the time for the most part, now that you have cleaned the condensor the high side pressure is dropping to low for good a/c performance.
 
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Old 06-21-03, 10:26 PM
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That makes sense. The fans cycle on at about 210 and cycle off at about 130.
What I can't figure out is why the air blows hot out of the grills as if the heat is on.
The control is set to max a/c but while the fans are running heat comes outa the grills. When the fan cycles off the heat slowly returns to cool. This started after washing the condenser.
I didn't really use a lot of water.
Is there a processor for the heat control?
 
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Old 06-22-03, 12:30 AM
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the heater blend door is probably electrically controlled as is most cars are now, but i dont see any reason for the blend door to change position when the fans come on it should only change if selected by the control head. there can be a noticable difference between passenger and drivers outlets usually the one closest to the evaporator will be colder,
ive seen cars that the a/c would blow cold but the engine would overheat do to the fan not functioning you replace the fan and then the a/c does not work due to the system being so low on freon, now that it has a working fan to cool the condensor it just short cycles.
on a 90 degree day the high side pressure on that van will probably be around 250 with both fans on at idle and the fans will not cycle cause they will never be able to lower the pressure enough when the temperature is that warm.
the only other thing i would check to make sure that the condensor didnt get damaged, 600 psi seems like alot to be using on a condensor that is probably either aluminum or plastic.
 
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Old 06-22-03, 06:23 AM
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bejay:

Thanks for your help. I agree that the heat thing is a kind of a strange symptom. He's going to the dealer tommorrow. I'll find out then I guess.

I doubt anything was damaged by the water. The washer I used was my "gentle" one I use for window a/c's and stuff.
This washer puts out 600 psi @ 1.5 gpm which is not much. My bigger one has a 5 hp Honda engine and puts out 2500 psi @ 2.5 gpm.
This one will bend aluminum fins.
 
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Old 06-22-03, 07:17 AM
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Greg H most automotive a/c systems are considered critical charge meaning a couple ounces more or less it won't work properly.GM went to a new a/c machine because of this fact.Auto a/c doesn't hold that much refrigerant compared to home a/c but you know that.Oil overcharges happen also because some people always add oil to the system when they charge it.I agree with Bejay it's probably low.I charge systems after evactuation and add the proper amount by weight.
 
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Old 06-22-03, 09:33 AM
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My mainstay is commercial HVAC/R and auto is something I care not to do because as you say this area is becoming extremly specialized. The principals are the same, but mfr's are pushing the limits of the tech, mostly to be able to make it cheaper.
I gave it up when a garage asked me to leak test a GM something and I couldn't even see the compressor. I could see the s/d lines going into a kinda black hole and could just feel the edge of the pulley, but couldn't see myself spending the morning pulling half the engine apart to do 20 minutes work.
I much prefer to be up on a roof on a hot sunny day fixing a gratefull club owner's a/c while his customers are walking out the door. Have you ever had a round of applause when you walk in the door after fixin' something?
I give you guys that work with the public a lot of credit. I'm sure you have a lot of appreciative customers, but it's been my experience that tradesmen seldom get the respect they deserve.
Enough rambling.

There was a presssure tap that had a warning tag that made reference to using a max 1 psi coil test pressure. Wassat?
 
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