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Low side gauge stays low

intedeco on Mon March 09, 2009 8:23 PM User is offlineView users profile

Year: 2001
Make: Freightliner
Model: FLD120
Engine Size: 430
Refrigerant Type: 134A
Ambient Temp: 80
Pressure Low: 10
Pressure High: 200
Country of Origin: United States

I have vacuumed the system and the reading was negative on the low side and zero on the high side. I let it sit for about 20 minutes and the low side stayed in negative. As such I assume there is no leak.

When I charged the system with 3 Lbs of 134A the high side goes up to 2.2 ambient temperature but the low side keep coming down to less than 10 after every can of freon.

Any help in diagnosing is greatly appreciated.

TRB on Mon March 09, 2009 8:27 PM User is offlineView users profile

Find out what the correct refrigerant capacity of the system is before doing anything else. Check for labels under the hood or in the owners manual.

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intedeco on Mon March 09, 2009 8:34 PM User is offlineView users profile

It is 3.0 Lbs R134a according to the label.

TRB on Mon March 09, 2009 8:40 PM User is offlineView users profile

Is it blowing could? Does it have a expansion valve or orifice tube? My bet is an expansion valve and at 80 degrees I'm thinking you are not far off on pressures.

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intedeco on Mon March 09, 2009 8:43 PM User is offlineView users profile

I should have mentioned it before. It is blowing hot air.

TRB on Mon March 09, 2009 8:47 PM User is offlineView users profile

Is the suction line cold at the evap and compressor. You did not answer what type of expansion device it has!

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intedeco on Mon March 09, 2009 9:00 PM User is offlineView users profile

Yes it has an expansion valve and the suction line was cold at the evaporator and dripped a little water.

TRB on Mon March 09, 2009 9:05 PM User is offlineView users profile

I would suggest checking other things like hot water getting in the heater core or blend doors not working correctly. Pressures show the evap is getting cold and you confirm this by touch on the return line. That means the core is cold so why are you not getting cold air out the vent?

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com


Edited: Mon March 09, 2009 at 9:05 PM by TRB

intedeco on Mon March 09, 2009 9:12 PM User is offlineView users profile

Thank you for the advice. I will check the blend doors tomorrow and et you know the outcome.

TRB on Mon March 09, 2009 9:19 PM User is offlineView users profile

Don't forget the hot water shut off valve leaking water back in the core. Not 100 percent sure how this system is designed. Depending on configuration cold air blowing through a hot heater core would eliminate all the cold air the evap produced.

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

TRB on Wed March 11, 2009 3:31 PM User is offlineView users profile

intedeco, thanks for supporting the forum it is much appreciated!

Did you find the problem with the freightliner?

-------------------------

When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

intedeco on Wed March 11, 2009 5:39 PM User is offlineView users profile

The truck has been on the road. I will have to wait for it to return. By the way, as you mentioned earlier these trucks use hot water from the radiator for heat. There are two valves that has to shut during the summer. I will have check whether that is why it is blowing hot air. Will kepp you posted with results.

JACK ADAMS on Thu March 12, 2009 3:23 PM User is offline

If you have the “T” handle style hot water valve that you manually turn off, replace them with a Brass Ball Valve. These will almost never go bad…. Home Depot has all differant sizes.

Good luck.

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