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2000 freighter fl70 ac blows cold but compressor not cycling


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Azusedoil
New User

May 29, 2018, 11:52 PM

Post #1 of 6 (371 views)
  post locked   2000 freighter fl70 ac blows cold but compressor not cycling  

Replaced sandon compressor dryer expansion valve. Flushed system, added correct amount and type of pag oil vac'd system ck'd system held vacuum for 4 minutes. This truck was not manufactured with ac had been added later so I can not get exact refrigerant charge from freightliner.initially charged with minimal amount allowed low and high side come to equalized pressures without system running around 80 psi.turned on ac blower high cab open clutch engaged suction side dropped to 10 high side about 100.temp at center vent 60 truck at idle added refrigerant till low side 30 high side about 150.temp center vent 50.kicked up idle to 1200 rpm low side drops to about 18 high side stayed about same.center vent about 45.left rpm at 1200 added little more refrigerant low side about 25 high went to about 175 center vent 42 degrees but compressor not cycling engine fan
will engage and bring low and high pressures down a little bit still no cycling if I pull connector off pressure switch on dryer compressor clutch will disengage and low side will immediately climb and high will drop plug it back in and clutch reengages and system goes back to previous pressures but still no cycling. Looking for a little guidance please


(This post was edited by Azusedoil on May 29, 2018, 11:59 PM)


Discretesignals
Ultimate Carjunky / Moderator
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May 30, 2018, 4:25 AM

Post #2 of 6 (346 views)
  post locked   Re: 2000 freighter fl70 ac blows cold but compressor not cycling  

The pressure switch on the receiver drier is actually a high pressure cutoff switch. Thermal expansion valve type systems usually won't cycle the compressor when the low side is low pressure as a ccot (cycling clutch office tube)system does. The expansion valve regulates the amount of refrigerant going into the evaporator. Most txv systems will have an evaporator temp switch that will cut off the compressor clutch if the evaporator temps gets to or below freezing.





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(This post was edited by Discretesignals on May 30, 2018, 4:31 AM)


Hammer Time
Ultimate Carjunky / Moderator
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May 30, 2018, 4:31 AM

Post #3 of 6 (340 views)
  post locked   Re: 2000 freighter fl70 ac blows cold but compressor not cycling  

Why are you expecting it to cycle? This is not a cycling system. It may have an anti-freeze switch in the evaporator but it is not designed to cycle regularly if it has an expansion valve.

Sounds like you are still a little light on refrigerant though. How much oil did you put in the system?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
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May 30, 2018, 7:47 AM

Post #4 of 6 (330 views)
  post locked   Re: 2000 freighter fl70 ac blows cold but compressor not cycling  

? Big rig stuff: Not my game but can't imagine not being a TXV set up as suggested with a failsafe to shut down so it doesn't freeze already mentioned. Unknown charge can be a challenge the maker probably can't know how it was set up to be that exact. Performance if warm enough out is good just know Tx systems can do that metering in just what it calls for.
This is probably an exception to the "site glass" doesn't count idea and probably has one on or near receiver-dryer if only a tiny thing you need to clean off to know there even is one if so takes a lot of guess work OUT of this.
BTW - I do suggest if at this again hold or lock it in state of vacuum for longer than that. 1/2 hour at least, longer even better. There is only a snag just heard of it if VERY cold out and working on one of these is ice if already inside system will not be pulled out so easily such that entire machine must be well above freezing otherwise should be all common sense physics. Relax - water would boil like on a stove in a vacuum, ice (not this time of year in most places) not the issue,


T



Azusedoil
New User

May 31, 2018, 7:12 PM

Post #5 of 6 (291 views)
  post locked   Re: 2000 freighter fl70 ac blows cold but compressor not cycling  

Don't know why I expected it to cycle,lack of experience i guess. Added little more refrigerant 42 degrees out of vent 42 in the evaporator. There is a thermostatic switch with capillary in evaporator if I pull off one lead disengaged clutch on compressor, so like hammertime said anti freeze. Gonna call it all good thank you for help.


Hammer Time
Ultimate Carjunky / Moderator
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May 31, 2018, 8:14 PM

Post #6 of 6 (287 views)
  post locked   Re: 2000 freighter fl70 ac blows cold but compressor not cycling  

Glad you got it working good. Closing this now as solved.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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