Intermittent airflow through Dash Vents

[JJPage]

I have read a couple hundred post on the AC systems the last couple of days, and the more I read the more I believe my evaporator is freezing up.



The AC will start out working great, lots of airflow(cold) through the dash vents. Within an hour the flow diminishes, until hardly any airflow at all is coming out of the dash, I switch to floor and defrost and not much better. The only thing that seems to help is to turn off the compressor switch, and after about ten minutes it begins to flow air again.



Having a background in Commercial HVAC, I understand that a low charge will lower temp along with pressure and could freeze the evaporator. I also read where the temp sensor has to be relocated on the evap coil.



Every once in a while, I can hear one of the heater doors thumping either open or shut, but just on start up of either the heater or AC, so I suppose I could have a malfunctioning door also.



What do you folks think? TIA, Jess

 

[sevobuck]

Mine makes that same thumping noise when I first turn the truck on. Mine is probably not one you should compare to since I am still having issues with the A/C. From my limited experience it does sound like your evaporator is either freezing up or dirty. Do you drive in dusty conditions often?

 

[BGlidewell]

check for proper charge.

 

[rbattelle]

My evaporator core has been freezing up for years now. I fix it by shutting off the compressor when airflow drops.

-Ryan

 

[JJPage]

Mine makes that same thumping noise when I first turn the truck on. Mine is probably not one you should compare to since I am still having issues with the A/C. From my limited experience it does sound like your evaporator is either freezing up or dirty. Do you drive in dusty conditions often?

Fairly certain it is not dirty, trucks not been off the asphalt but once or twice since new. If it was plugged with dirt/debris, I do not believe it would flow decent for the first hour. When airflow returns, it happens pretty quick, not like it's thawing out slowly. Thanks for the idea of dirt. . hadn't really considered that.

check for proper charge.

I have only worked with R-11, R-12, and R-22 systems, I know what their pressures should look like, do you know what acceptable pressures would be for 134A? Guess I could Google it.

 

[goatnram]

i have the same problem i just shut off the a/c for couple minutes then turn it back on this a/c kicks butt when it is not froze up the coldest a/c i ever had i would hate to lose this air it is pain when it stops blowing

 

[BGlidewell]

Fairly certain it is not dirty, trucks not been off the asphalt but once or twice since new. If it was plugged with dirt/debris, I do not believe it would flow decent for the first hour. When airflow returns, it happens pretty quick, not like it's thawing out slowly. Thanks for the idea of dirt. . hadn't really considered that.

I have only worked with R-11, R-12, and R-22 systems, I know what their pressures should look like, do you know what acceptable pressures would be for 134A? Guess I could Google it.

low side should be 35-45 or so, there is a chart someone posted based on ambient temperature as well. A search would bring it up. An over charge will cause poor cooling as well. Undercharge will cause quick cycle of the compressor too.

 

[JJPage]

My evaporator core has been freezing up for years now. I fix it by shutting off the compressor when airflow drops.



-Ryan

i have the same problem i just shut off the a/c for couple minutes then turn it back on

I am not certain the evap is icing up, but I have my suspicions. I have been shutting mine off also, and 10 minutes later it works fine again... . I have not seen an evaporator on any of the systems I have worked on, thaw out that fast.

low side should be 35-45 or so, there is a chart someone posted based on ambient temperature as well. A search would bring it up. An over charge will cause poor cooling as well. Undercharge will cause quick cycle of the compressor too.

Thanks for the link. I believe I will check it tomorrow using this info, tells me what the equalized pressure should be on a 134A system at a given ambient temp.

86# @ 80*

104# @ 90*

147# @ 100*

172# @ 120*

It is supposed to be 90* tomorrow, so my static pressure should be around 104#, if less, then I maybe low on charge.