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pens66 06-18-2008 10:02 PM

Freezing pipes on a heat pump

I bought a Lennox heat pump last summer - it is an add on to an existing oil furnace. Since purchasing I have had nothing but porblems. The service techs have been back at least 8 times. The majority of the problems occur when I switch between heating and cooling.

The heating now seems ot work fine, but whenever I switch to cooling, cool air blows for a few minutes, then the pipes going to the inside of the furnace accumulate significant frost and the cool air doesn't blow.

Before getting the service people hear yet again - does anyone have any suggestions.

Thanks in advance.

P.S. I have replaced my furnace filter, and shut the breaker off/then on again to reset the system.

geo fan 06-19-2008 08:27 AM

fan filter freon
if the filter is clean what you can do is get the model and serial of the furnace and find out how many cfm's of air it can move and compare this to the ton's of the ac system you need 400 cfm per ton . the other thing it could be and the more likely is you are low on refrigerent this could be a leak in the system or improper charge . you can not acuratly charge a system if its a piston below 60 outside and if its a txv below 65 the system will not have enough head pressure for the metering device to meter properly. You most likely have a aux heating element which is why it seems to be working in the winter

pens66 06-27-2008 07:14 AM


As an update - I am now in another $1K in servicing costs for this problem.

Solutions tried to date include:
1. Overall check of system for proper amounts of refridgerant, valves, etc
2. Installing a stronger furnace motor blower,
3. Pumping and replacing the fluids in the outside unit,
4. REinstalling the indoor coil (moving the setup from being installed directly flush with the top of the furnace unit to leaving a six inch gap to allow more air circulation within the furnace unit - not sure if this is a requirement).

Problems continue - on the warming mode, it just blows air and does not change the indoor temperature. In the cooling mode, the pipes freeze up and minimal air flow occurs and the indoor temperature does not decrease.

Anyone have any further suggestions? All the techs say the heat pump unit is fine - am I getting to a point where a complete removal and reinstall will all new parts makes most sense? THat was basically done yesterday

glennjanie 06-27-2008 06:33 PM

Welcome PenS66:
It is normal for the suction (larger line) to frost over at times; it simply means your blower is not exchanging enough ari to use the amount of refrigerant metered into the coil. However, that should not prevent cooling. Can you look at the evaporator coil when this occours and see if it is also iced up? Too much frost on the coil will prevent the full flow of air.

kok328 06-28-2008 06:07 PM

Another possiblity could be a restriction of non-compressable subtance or a blockage in the filter/dryer.
You'll need a set of HVAC guages designed to measure your particular type of freon.

Geo Fan - Please correct me if I'm wrong but, if you totally evacute the system and recharge the system using a scale and install the specified lbs. & ozs., wouldn't this system be properly charged regardless of ambient tempature being that freon does not vary in weight based on tempature?

I fully understand the labor involved in this technique but, it does provide for fool proof results instead of a return call on a warmer or cooler day for high or low head pressure cut out.

geo 06-28-2008 07:29 PM

the factory charge the amount on the nameplate is sufficiant to acomodate for 15feet of lineset and a matching coil no more no less it is not that simple i wish it was but the only way to charge properly is by using the super heat and subcool calc

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