On TXV systems does compressor cycle ? Intended function of high pressure switch

Friendly format provided to inquire about automotive a/c systems.
Archived Forum

Moderators: bohica2xo, Tim, JohnHere

Post Reply
r-mm
Posts: 31
Read the full article
Joined: Sun Jul 01, 2018 1:25 pm

On TXV systems does compressor cycle ? Intended function of high pressure switch

Post by r-mm »

I have a 1989 BMW 325i with an expansion valve as attached. On such a system does one expect the compressor to cycle on and off via the high pressure switch on the receiver/dryer, or does the expansion valve control the flow of refrigerant and therefore how hard the compressor is working?
Attachments
open-uri20140912-27477-1x8o6k7_.jpg
open-uri20140912-27477-1x8o6k7_.jpg (120.61 KiB) Viewed 4190 times
User avatar
Cusser
Preferred Member
Posts: 846
Joined: Sun Apr 24, 2016 6:29 am

Re: On TXV systems does compressor cycle ? Intended function of high pressure switch

Post by Cusser »

On my 1988 Mazda truck, and my 1998 and 2004 Nissan Frontiers - all which have expansion valve systems - the de-icer switch on the evaporator case (which has a sensor in the evaporator fins) makes their compressors cycle.
User avatar
JeremyB
Posts: 7
Joined: Thu Jul 07, 2016 12:43 pm

Re: On TXV systems does compressor cycle ? Intended function of high pressure switch

Post by JeremyB »

The TX valve just controls superheat of the evaporator. Depending on conditions, the evaporator could be at 35 degrees or 55 degrees with the same amount of superheat. Once the evaporator pressure (and temperature) drops below the switch setpoint, it opens to prevent evaporator freezup.

Not familiar with that BMW, but a high pressure switch on the receiver will shut off the compressor if the high side exceeds maximum pressure of the switch.
Post Reply