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waynezo

AC Problem 08 Milan 4 cyl 83k

Question

Compressor is short cycling. Still cooling the cabin, but poorly. I checked Refrigerant.  It
is not low.  I suspect the AC clutch switch.  I found it on the smaller high pressure tube
near the firewall.(part# MOTORCRAFT YH39 Alternate/OEM Part Number(s): 6E5Z19D594AA)

Is this the only pressure switch or are there 2?  Is there a way I can diagnose with out
putting in the shop.  Looks like I can change the switch myself.

When the compressor is engaged air is ice cold.  What else would cause these symptoms?

Any advice is greatly appreciated. 

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Autozone will lend me manifold gauges.  can you recommend a good tutorial for diagnosis.  All fan speeds work on control head.

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What are your running pressures when the clutch kicks out? Does that agree with the AC pressure sensor as read by the PCM? Does the AC evaporator temp sensor agree with the outlet temp at the vents?  

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I measured with manifold gauges with ambient Temp at 86 degrees.

The low side is 40 to 45 (sometimes as low as 35) with compressor engaged then goes up to 60 after compressor kicks off.
The high side is 200 to 210 then down to 175 after comp kicks off
Static reading is low side 100 high side 125 

Does that indicate a low side switch?

The schrader valve on the low side access port has a slow leak I noticed after removing the gauge. The cap seems to be holding it for now. Is there a way to get it to seat properly without replacing it?

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I tightened the schrader valve and it stopped leaking.   Early this morning with ambient temp at 75 degrees I got 35 lowside and 157 highside.  After adding approx 4 oz of refrigerant with ambient temp at 80 degrees I get lowside 40 and highside 225.  AC is still short cycling.  Should I worry system is now overcharged?

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There is no low side switch. There is a high side pressure sensor and an evap temp sensor. Your pressures look ok. Now you need a capable scan tool to compare your pressure to the pressure sensor and watch the temp sensor, and PCM commanded clutch control vs actual. 

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Thanks for all the great advice. 

My car has the expansion valve. I spotted it on the firewall where the lines attach.

One other symptom I have had. Previously When sitting at a red light in gear when the compressor kicks on the engine shudders. Since I have noticed it short cycling it shudders less. Could that be a sign of the compressor wearing out and putting less strain on the engine?

What is a good scan tool?  I'm guessing I would have to buy that.  Autozone probably won't loan it.

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I put the car in the shop the tech said I have a blockage and he found metal in the system. He referred to it as the "black death". He said the evaporator is ok but I should replace compressor, expansion valve, and condenser. He said the dryer is located in the condenser and the labor is the same so I should pay a little more for a new condenser since a lot of debris lands in the condenser.
Sounds reasonable to me. Your Thoughts?
Any opinions or advice are appreciated.

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If the system is contaminated yes he is correct. The condenser does contain the dryer and it should be replaced. He can flush the evaporator and any lines that don’t have an “muffler” on them. That’s means straight lines with no cylinder looking piece in it somewhere. 

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I had the repair done and AC blows ice cold.  

Now after about 20 mins on the highway when I put the fan on high airflow is weak.  If I turn it off for a few minutes it returns to full blast.  Sometimes it starts weak then after 30 secs blows strong.  I suspect the blower motor is starting to fail.

I inspected the connector to the resistor without disconnecting it.  The wires look pristine not melted.  The blower motor was replaced aprox 5 years ago.  All my fan speeds work.  Should I replace just the blower motor or both the motor and resistor?

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27 minutes ago, waynezo said:

I had the repair done and AC blows ice cold.  

Now after about 20 mins on the highway when I put the fan on high airflow is weak.  If I turn it off for a few minutes it returns to full blast.  Sometimes it starts weak then after 30 secs blows strong.  I suspect the blower motor is starting to fail.

I inspected the connector to the resistor without disconnecting it.  The wires look pristine not melted.  The blower motor was replaced aprox 5 years ago.  All my fan speeds work.  Should I replace just the blower motor or both the motor and resistor?

“The works for 20 mins on the highway” sounds almost like the evaporator is icing up. Did you ever have the discharge temp sensor checked in the dash? You would know because it needs a scan too to check and also the dash has to be tilted back to access.  

Side note. I saw a fusion that someone bypassed the compressor relay to make it work. When it was a bad discharge temp sensor. Their theory was the expansion valve would keep it from freezing. However, that’s not the case. 

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I don't know if he checked the sensor.  Is there a way I can check for freezing?  Sometimes it starts slow and then spins up to full speed.  When the airflow is weak I don't hear any fan noise.

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4 hours ago, waynezo said:

I don't know if he checked the sensor.  Is there a way I can check for freezing?  Sometimes it starts slow and then spins up to full speed.  When the airflow is weak I don't hear any fan noise.

It’s very possible you have a blower motor  failing. An easy way to tell is run the blower with out the AC button on for a day or so and see if it still does it. That would give you an idea if it’s a icing issue or a blower issue. Make sure the isn’t compressor running when the ac button is not illuminated.

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OK thanks.  I will do that.  If it is an icing issue is there anything besides the evap sensor that would cause it?  I heard the evap sensor is a $20 part but 8 hours labor cause you have to pull the dash.  I can change the blower motor myself but I guess it is a strange coincidence for it to fail right after I had the other work done. 

Thanks for the advice.

 

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19 hours ago, fordtech1 said:

It’s very possible you have a blower motor  failing. An easy way to tell is run the blower with out the AC button on for a day or so and see if it still does it. That would give you an idea if it’s a icing issue or a blower issue. Make sure the isn’t compressor running when the ac button is not illuminated.

Compressor disengages when I turn AC button off.  When I turn the thermostat knob into the red I get heated air but AC button stays lit and compressor stays engaged.  Compressor doesn't cycle off.  Is this normal?  Do I have a Variable displacement compressor?

 

After a 40 min run I get weak airflow.  If I turn off the AC button within 2 min strong airflow returns.  Sounds like you are right evaporator is icing up.  I will have to take it back to the shop.  Can the icing issue be caused by anything other than the temp sensor?

Edited by waynezo

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It could freeze from over charge, bad discharge temp sensor, poor air flow through evaporator. Expansion valve can cause it also. My recommendation would be to have them check the what the pcm is seeing from the discharge sensor. I have changed a ton of those sensors but all I can remember caused ac inop. They all were reading -40 degrees. However that’s not to say it can’t go the opposite way. I would put a thermometer in center vent and watch the sensor pid and see if they agree. 

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On 3/31/2019 at 4:56 PM, fordtech1 said:

It could freeze from over charge, bad discharge temp sensor, poor air flow through evaporator. Expansion valve can cause it also. My recommendation would be to have them check the what the pcm is seeing from the discharge sensor. I have changed a ton of those sensors but all I can remember caused ac inop. They all were reading -40 degrees. However that’s not to say it can’t go the opposite way. I would put a thermometer in center vent and watch the sensor pid and see if they agree. 

Yes it was the evap sensor.  Tech said he was getting 38 degrees at the vents but never lower than 71 degrees from the evap sensor so the comp never disengaged freezing up the system.  He said usually they default to -40 degrees.  This is the first one he saw go the other direction and he has done a ton of them.

Thanks again to all who responded.

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On 3/7/2019 at 3:12 AM, waynezo said:

Compressor is short cycling. Still cooling the cabin, but poorly. I checked Refrigerant.  It
is not low.  I suspect the AC clutch switch.  I found it on the smaller high pressure tube
near the firewall.(part# MOTORCRAFT YH39 Alternate/OEM Part Number(s): 6E5Z19D594AA)

Is this the only pressure switch or are there 2?  Is there a way I can diagnose with out
putting in the shop.  Looks like I can change the switch myself.

When the compressor is engaged air is ice cold.  What else would cause these symptoms?

Any advice is greatly appreciated. 

Word of advice please, be VERY CAREFUL when working with ANY refrigerants, safety glasses/goggles are a MUST.

Why am I concerned? As a just retired firefighter I've seen enough incidents where the HVAC tech was not wearing proper PPE, resulting in bodily harm, like being blinded permanently.

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